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Chapter 1 Lab Group: Alyssa, Kelsey, Dana, Ashley

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Grade:

Chapter One

What Do You See/What Do You Think

Chapter Two

I see a car accident ahead of the road and then I see a speeding driver who is trying to stop short. The driver was probably distracted by the bunny rabbit or the mountains. The factors that affect the time you need to react to an emergency situation while driving are; the speed you were going, the size of the vehicle, the road conditions.

Table of Contents Section 1 Section 2 Section 3 Section 4

Measuring Time to Move Your Feet

Section 5

It took Ashley 3.34 seconds to move her foot from gas to break 10 times. It took Ashley .53 seconds to move her foot from gas to break one time.

Section 6 Section 7

Investigation: Measuring Reaction Time Method A The first reaction time was .22 seconds. The second reaction time was .13 seconds. The third reaction time was .23 seconds. The average reaction time was .19 seconds. Method B 5 inches, .23 seconds 4 inches, .27 seconds 4 inches, .10 seconds The average is .20 seconds Method C (green red) .19 seconds .68 seconds .95 seconds .22 seconds .21 seconds The average is .45 seconds 1. Our reaction time when needed to make a decision is greater than the reaction time without needing to make a decision. 2. This experiment applies to road hazards because it tells us that it is much harder to react to an accident if your distracted by something. Method D (texting) .54 seconds .43 seconds .67 seconds .25 seconds .36 seconds The average is .45 seconds 1. When you are distracted by texting, it makes your reaction even slower. 2. Your ability to avoid road hazards is very poor when you are distracted by texting or scenery. Homework Physics Talk Checking Up (p.13) 1. How do distractions affect reaction time? Distractions make your reactions slower. If a decision has to be made suddenly, distractions may cause a collision. 2. Why is driving under the influence of alcohol or drugs illegal? It is illegal to drive under the influence of drugs and alcohol because they can slow your reaction time greatly. Even legal drugs can do this to you. 3. Name three factors in addition to distractions and drugs or alcohol that can affect reaction time. Three factors that can slow your reaction time are road conditions, scenery, speed of the vehicle, and size of the vehicle.

September 8th 2011 Reaction Time: Science of the Fastball 1. How long does it take a fastball to reach home plate? (The application tells you if you click "continue") It takes a fastball half a second to reach home plate. 2. Why if your reaction time is under .5 seconds do you still sometimes not hit the ball? Just because you react very quickly, does not mean that you will always be accurate. 3. Explain what else might take some time before you hit a pitch besides imply reacting to it? Likewise when you are driving what else do you need to do besides react to an obstacle before you come to a stop? Before you hit a pitch, you need to make sure that you keep your eye on the ball. This will ensure that you make contact, and actually hit the ball, instead of just swinging and missing. While driving before reacting to an accident, you need to check your surroundings. If you need to swerve out of your lane and into another one, you need to make sure there is no oncoming traffic. 4. Can you really hit a 90 mph fastball? What factors are not included in the program that decide whether you could hit that ball in real life? (Think back to the reaction time investigation) Other factors that are involved in hitting a 90 mph fastball are making contact with the ball, the speed in which you are swinging. Also, you need time to consider whether the pitch is a strike or ball. 5. What strategy might you use while driving to reduce reaction time once you are alert to a possible obstruction? In the same way what might a batter do to reduce reaction time once they are alert to an incoming pitch? kIf you see a car pulling out in front of you, you can put your foot over the break. This way, you can reduce the time it takes you to react. A batter might shorten up their swing for a faster pitch to reduce the time it takes to swing the bat. 6. Why might someone yell from the dugout at a batter, "hey batter batter swing batter batter!", when the batter is trying to hit the ball? How is this similar to texting while driving. Well, just like texting distracts you from driving, someone yelling at you while you are trying to concentrate is definitely considered a distraction. The opposing team would yell this at the batter to distract them, and hopefully cause them to strike out. Active Physics Plus d=1/2at^2 (cm)=1/2(cm/s^2)(s)^2 d: distance any object falls in a time "t" (s) t: time any object falls a distance "d" (cm) a: acceleration of any object falling (980cm/s^2)

Time Distance .025s .31cm .05s 1.2cm .075s 2.7cm .1s

4.9cm

.125s 7.6cm .150s 11.02cm .175s 15.01 .2s

19.6cm

.225s 24.81

September 12th 2011 Do Now 1. Does a race car driver need a faster reaction time than someone driving in a school zone? Explain your answer, giving examples of the dangers each driver encounters. Yes, a race car driver needs a faster reaction time. A faster car will cover more distance in the same amount of time compared to a slower object. Can You Catch A Dollar Bill? Max distance dollar bill can drop: 15.55cm=d (d=1/2at^2) 15.55cm=1/2(980cm)t^2 31.1cm=(980cm)t^2 .031s^2=t^2 Take the square root .18 s=t Reaction time to catch the bill: Reaction Time Ruler

Homework Parents Reaction Time .15 .23 .25 .23 .26

September 14, Wednesday Do Now- Physics To Go Section 1 #6 and 7 pg. 20 1. What are the consequences of driving when one's reaction time is slow rather than quick? The consequences could potentially be an accident, resulting in death or an injury. 2. Even though teenagers often have good reaction times, why is auto insurance more expensive for teenage drivers thanit is for older, more experienced drivers? Teenagers statistically engage in more distractions such as; texting, talking, listening to loud music.

Reflecting on the Chapter Challenge p.18 1. What are the top two causes of accidents on the road? The top two causes are driving with fatigue and rubbernecking. 2. What is rubbernecking? Does rubbernecking constitute a decision or distractions? Rubbernecking is being distracted by things going on around you, such as scenery or an accident. Rubbernecking counts as a distraction.

Section 2 Grade: 100 September 15, Thursday Measurement: Errors, Accuracy, Precision What Do You See/What Do You Think? I see a man walking with a little girl following behind. There is another guy with a tape measurer They seem to be measuring their strides 1. Two students measure the length of the same object. One reports a length of 3 m, the other reports a length of 10 m. Has one of them made a mistake? Yes, i think one of them definitely made a mistake because it is impossible to have that much of a difference between two measurements of the same object. 2. If the students reported measurements of 3 m and 3.01 m, do you think one of them has made a mistake? No, I don't think either of them made a mistake. They just didn't get the exact same measurement. September 16, Friday Investigation Lab for Section 2 It took Ben 18 strides to get from one piece of black tape to the other. Each of Ben's steps are .5 meters. In conclusion, the distance between the two pieces of tape is 9 meters.

1. Do the measurements in your class table agree? They all vary based on the group and size of stride. 2. By how many meters do the results vary? Some of the results vary by about 3 meters 3. Why are the differences in the measurements made by different groups? List as many reasons as you can think of. If a stride was not measured just like the person walks then the measurements would be off. Also with rounding, measurements can be off by a larger number once multiplied. 4. Suggest a method of making the class' measurements more precise. If all groups use your suggested method how will this reduce the range of measurements collected? I think if everyone used the two meter sticks the measurements would be more precise. 5. What do you think would happen if each group were given a really long tape measurer? Do you think each group would get the exact same value? Why or why not? Yes, I think every group would get the same value because we would all be able to get exact measurements. 6. Can you develop a system that will produce measurements that would agree exactly or will there always be differences in measurements? Justify your answers. No, you cannot develop a system that will be exactly the same every time because there is no possible way of getting the same answers every time. 7. 8. Read #8 on p.23-24 in your book then answer letters A and B in your wiki. (when they say "using each technique in letter"b" they mean "strides or meter stick?" technique). The strides could have produced a systematic error, moving the meter sticks could have produced a systematic error, and someone's foot size could have produced a systematic error. Homework In this section I will learn: To identify mistakes and errors in measurements. Calibrate the lengths of a stride. Measure a distance by pacing and using a meter stick. Decide if measurements arereasonable or unreasonable. Physics Words Systematic error- An error when using a tool incorrectly for a measurement and can be corrected by calculation. Accuracy- How close a series of measurement are to the actual measure. Precision- An indication of the frequency in which a measurement produces the same results. Checking Up Questions 1. Explain the differences between systematic and random errors. Systematic error is using a tool incorrectly and random errors are errors that can not be corrected by calculating. 2. Explain why there will always be uncertainty in measurement. Because the person using the tool wont always be completely accurate. 3. What would the positions of arrows on a target need to be to illustrate measurements that are neither accurate nor precise. If all the arrows were all over the target and not close together. September 19, Monday Do Now: Physics Talk

Demo: How Long is the Tube? (4 sided ruler) Interval1Meter.1Meter.01Meter.001Meter .8m .8m .85m .832m .8m .85m .84m .83m .8m

.85m .83m .82m .84m .83m .83m .82m .817m .81m .825m

.81m .812m .813m .809m .81m .82m .815m .82m .812m

Physics Talk Notes- SI System Quantity Unit

Symbol

DistanceMeter

M

Mass

Grams

G

Time

Seconds S

September 20, Tuesday Measuring a Copper Tube Groups Measurements G1

66cm

G2

64cm

G3

66cm

G4

64.1cm

G5

66cm

G6

64cm

Active Physics Plus p.29 1. Uncertainty: +10cm --> +10(.10)m--> +.1m(50.1m-49.9m)Range +1cm--> + 1(.01)m-->+ .01m(50.01m-49.99m)Range +1mm-->+1(.001)m-->+.001m(50.001m-49.999m)Range 2a. Faster s=d/t d=50m t=25s s=50/25 s=2m/s 2b. Faster s=2m/s s=d/t d=.02 (t)s=d/t(t) (t)s/s=d/s t=d/s t=.02m/2=.01s 3. 30 laps .02m X 30 laps= .6m 1500.3 -- 14.997 (range) s=d/t=1500m/15(60s)= 1.7m/s t=d/s t=.6/1.7 t=.36s Physics to Go: p.33, 3, 4, 6, 7, 8, 9 3.Give an estimated value of something that you and your friend would agree on. Then, give an estimated value of something that you and your friend would not agree on.Something we would agree on is something like how many poms we need for a performance. We might not agree on measuring something using a measuring stick because sometimes you can pull the tape out too far and that would be a systematic error. 4. An oil tanker is said to hold five million barrels of oil. In your estimate, how accurate is the measurement? Suppose each barrel of oil is worth $100. What is the possible uncertainty in value of the oil tanker’s oil? Our estimate was probably not exactly accurate. The uncertainty could be drastically different because if you're off by even one barrel, the money is off as well. 6.Are the following estimates reasonable? Explain your answers. a) A 2-L bottle of soft drink is enough to serve 12 people at a meeting. b) A mid-sized automobile with a full tank of gas can travel from Boston to New York City without having to refuel. I think that example is A is reasonable, but example B is not. In example A you can evenly distribute the soft drink, while your'e driving you are not always going a constant speed and maybe come to a stop which keeps using gas. Unless, of course, you are using cruise control. However, this would have to be portrayed in the information beforehand. 7.If you are off by 1 m in measuring the width of a room, is that as much as an error as being off by 1 m in measuring the distance between your home and your school? An error in measuring your room is a bigger error. From your house to your school is a greater distance, so there is more room for error. More room for error means that it is going to happen more often for a greater distance. 8.You are driving on a highway that posts a 65 mi/h (105 km/h) speed limit. The speedometer is accurate within 5 mi/h (8 km/h). a) What speed should you drive as shown on the speedometer to guarantee that you will not exceed the speed limit? You should drive at least 60miles/hour just incase. this is because if its range is within 5miles/hour then you want to be a little slower so that you are not going too fast. If you tried to keep the speedometer on exactly 65 miles/hour then you might be 5 miles/hour over the speed limit. b) What could a passenger in the vehicle do while you are driving to estimate how accurate the speedometer is? (Hint: The road has mile markers, and the passenger has a wristwatch that shows seconds.) You could use a smaller measurement of speed to see how fast you are going to compare to the mile markers on the highway. You can use the formula D=S/T to see how fast you are going. 9.Preparing for the Chapter Challenge Many accidents are caused by speeding. To limit the number of collisions, police officers give speeding tickets to drivers. If the speed limit were 30 mi/h (50 km/h) in a residential neighborhood, a person may get a ticket for driving at 40 mi/h (65 km/h). Legally, they could also get a ticket for traveling at 31 mi/h (51 km/h). Given the uncertainties in measurements (the driver has to keep the gas pedal “just right”), you may wish to mention how these uncertainties are a part of safe driving. You may wish to explain why driving 31 mi/h in a 30 mi/h zone does or does not warrant a ticket. If you do not think that 31 mi/h deserves a ticket, you will need to explain what speed should get a ticket and why. I disagree. The leeway should be at five miles per hour or more because if you're just a half a mile per hour over the speed limit you can get a ticket. It makes it extremely hard to go the exact speed limit. Inquiring Further 1. If you were going to be buying vegetables it should be by the weight of the total products that you are buying, while gasoline should be by the barrel. Also Carpeting should be by the foot. September 21, Wednesday Do Now: Section 2 p31 What Does it Mean? Suppose your friend mistakes a yardstick for a meter stick and measures the length of an intersection in your neighborhood. Is this error random or systematic? Which of these types of errors affect precision or accuracy? This is a systematic error because it affects accuracy.

Why Do You Believe? All physics knowledge is based on experimentation. All experiments require measurements. How can you trust experiments if all measurements have uncertainties? Even though everything has uncertainties, the numbers wont be too far off. This means the numbers will be pretty accurate, if not exact Reflecting on the Section and the Challenge A measurement is never exact. When you make a measurement, you estimate that measurement. All measurements have systematic and random errors. An example of a systematic error might be using a measuring tape that stretches a little bit when it is pulled tightly. But if you know the amount of stretch, then you can correct the measurement using calculations. In contrast, random errors are part of any measurement process because you can only approximate a mark on a meter stick or the time on a stopwatch, with an accuracy to the closest decimal place. You can try to minimize random errors, but you cannot eliminate them entirely.When a speed limit is 60 mi/h (about 100 km/h), you may find that sometimes you drive at 58 mi/h while other times you drive at 62 mi/h. These differences are random errors as you try to hold the speed constant. If a police officer stops you because you were driving at 75 mi/h (about 120 km/h) in a 30 mi/h zone, you will not be able to convince her that this was just an uncertainty in your measurement. Uncertainties in speeds may be something that you wish to include in your presentation or report. You go 75 mph in a 30 mph zone. you explain to the police officer that his reading on his radar is due to the uncertainty in the instrument. Is this valid? No, this is not valid at all. Uncertainty in the instrument is quite possible, however the uncertainty

would not be a 45 mph difference. Estimation Activity: Investigation p. 24 #9 A-I 9. Sometimes a precise measurement is not needed. A good estimate will do. What is a good estimate? Use your common sense and prior knowledge to judge if the following measurements are reasonable. Explain your answers. A. A college football player has a mass of 100 kg (weighing about 220 lb). Yes, most football players are around 220 pounds. B. A high-school basketball player is 4 m (13 ft) tall. No, this is an abnormal height even for a fully grown adult. C. Your teacher works 1440 min every day. No, my teacher does not work 19 hours a day. D. A poodle has a mass of 60 kg (about 132 lb). No, that is an absurd weight for a dog. E. Your classroom has a volume of 150 m3 (about 5300 ft3). No, that is a huge classroom. F. The distance across the school grounds is 1 km (about 0.6 mi). No, this is way too long for school grounds. G. On a rural road, while driving 50 mi/h (about 80 km/h), you a tractor moving very slowly. You are about 1⁄4 mi (0.4 km) away when you see that another automobile is coming toward you, travelling at 50 mi/h. Is it safe to pass the tractor? Yes,this is safe to pass the truck because of how slow it is moving. H. While driving your pickup truck on a rural road, you approach a narrow bridge and see you will reach it at the same time as a dump truck that is coming from the opposite direction. What must you estimate in order to decide whether to stop and wait for the dump truck to cross the bridge first, or to go ahead and squeeze by the dump truck while on the bridge? You need to estimate the width of the bridge and the truck. I. You are driving a motor home with bicycles standing upright on a bicycle rack on the roof. a sign before the entrance to a title states that the maximum height is 21ft (6.4m). Will your automobile make it safely through the tunnel? Yes, I think the automobile will make it.

Section 3 Ashley M ch1s3.docx Details Download 55 KB

Grade: Average Speed: Following Distance and Models of Motion September 23, Friday Do Now: What Do You See/What Do You Think? I see a picture of an accident involving three cars. It appears that one car was rear-ended, and then another driver who wasn't paying attention rearended the other car. What is a safe following distance between your automobile and the vehicle in front of you? 1 car length for every 10 mph will set a good distance between you and the car in front of you. How do you decide what a safe following distance is? You can use the three second rule. Investigation: p. 34-36 #4/6 Distance v. Time Graphs 1a) 30 mph

2a) 45 mph

2b.The automobiles who were each traveling 45 miles per hour were farther apart because they covered more distance in the same amount of time. The car going 45 miles per hour goes .75 miles per second. The car going 30 miles per hour goes .5 miles per second. 2c. 60 mph

3a. In which diagram is the automobile traveling the slowest? In which diagram is the automobile traveling the fastest? Explain how you made your choice. Yes all the cars are traveling at the same speed because there is the same distance between all three cars so they must be going at the same speed. 3b. Is each automobile traveling at a constant speed? How can you tell? Yes all the cars are traveling at the same speed because there is the same distance between all three cars so they must be going at the same speed. 4a. Sketch the graph of a person walking toward the motion detector at a normal steady speed.

.

4b. Sketch the graph of a person walking away from the motion detector at a normal speed.

4c. Sketch the graph of a person walking away from the motion detector then toward it at a very slow speed.

4d. Sketch the graph of a person walking in both directions at a fast speed.

4e. Describe the similarities and differences among the graphs. Explain how the direction and speed that the person walked contributed to these similarities and differences. Both graphs where Dana only walked in one direction, the graph is just one line. In the ones where she went away from and towards the motion detector, the graphs have two lines that meet at a point. The graph where Dana walked slowly, the points were more spaced out on the graph, and the one where she walked fast they were closer together. 5a.

5b.

6a.

6B:The points on the line where I walked faster would be closer together, so you can tell that line is the faster one, and the line where I walked slowly the points on the line would be farther apart because of my slower speed. 7A: In trial 1 I walked about 3.13 m and i walked a little bit more in the second trial, but just at a different speed 7B: TRAIL 1: about 5.2s TRIAL 2: about 2.95s 7C: AVERAGE SPEED TRIAL 2: (2.25m+2.95s)=5.2m/s 0.98 (average speed) TRIAL 1: (3.13m+5.2s)=8.33m/s 0.60(average speed) 7D: You could plug in the average speed and time into the equation, v=d/t. 8A: (60ft/s)(.5s)=30ft 8B: (60ft/s)(1.5s)=90ft 8C: 8a) (50ft/s)(.5s)=25ft 8b) (50ft/s)(1.5s)=75ft 8D: 8a) (70ft/s)(.5s)=35ft 8b) (70ft/s)(1.5s)=105ft 8E: (40ft/s)(.5s)=20ft 40ft-20ft= 20ft 8F: .25 lengths per second September 26, Monday DO NOW 1. An automobile is traveling at 90ft/s (60mph). If the driver's reaction time is .6s, how far does the automobile travel during this time? s=d/t d=s(t) d=(90ft/s)(.6s)=54ft 1. How much further will the car travel if the driver is distracted by texting, so that reaction time is increased to 1.5s? d=(90ft/s)(1.5s)=135ft

Physics Talk: Checking Up p. 43 Physics Words Speed: The distance traveled per unit time, speed is a scalar quantity, it has no direction. Constant Speed: Speed that does not change over time. Average Speed: The total distance traveled divided by the time it took to travel that distance. Instantaneous Speed: The speed at a given moment. Velocity: The speed in a given direction. Doppler Effect: The change in the pitch, or frequency of a sound or wave for an observer that is moving relative to the source of the sound or wave. Reaction Distance: The distance that vehicle travels in the time it takes the driver to react. Checking Up Questions 1. Explain how the average speed of a vehicle is different from instantaneous speed. It's different from being the speed at a given moment so the average is usually different. 2. How are the speed and velocity of an object different? The speed is how fast it's going while the velocity is is the speed and direction. 3. If the distance-time graph shows a straight, inclined line, what does the line represent? That the person is traveling faster as time keeps progressing. 4. How does reaction time affect reaction distance? Because it's the amount of time it affects a drivers reaction. PHYSICS TO GO pg. 49-51 #1-11 1. Describe the motion of each automobile below. The diagrams of strobe photos were taken every 3 s (seconds).

Screen_shot_2011-09-28_at_9.01.03_AM.png

a.) The cars are traveling at the same speed because they are the same distance apart. They're driving at a constant motion at a slow speed. b.) They cars aren't traveling at a constant motion because in the beginning the cars start to travel faster because they get farther apart. Towards the end they start to travel at a constant speed. 2. Sketch diagrams of strobe photos of the following: a) An automobile starting from rest and reaching a final constant speed. b) An automobile traveling at a constant speed then coming to a stop.

3. A race car driver travels at 350 ft/s (that’s almost 250 mi/h) for 20 s. How far has the driver traveled during this time? (350ft/s)(20s)=7,000ft 4. A salesperson drives the 215 mi from New York City to Washington, DC, in 4.5 h. a) What was her average speed? (215mi)/(4.5h)=47.8 mph b) Do you know how fast she was going when she passed through Baltimore? Explain your answer. You don't know because she could have slowed down due to traffic or and accident. The weather could have been bas as well so it's pretty likely she didn't maintain a constant speed the whole way through. 5. If you planned to bike to a park that was five miles away, what average speed would you have to maintain to arrive in about 15 min? (Hint: To compute your speed in miles per hour, consider this: What fraction of an hour is 15 min?) 15min=.25h (.25h)/(5mi)=20mph 6.

a) The driver was driving fast at first, then maintained a constant speed the rest of the way. b) The driver started off very fast, then a constant speed, then slowed down gradually at the end. c) The automobile slowly increased in the beginning than suddenly increased in speed. d) The automobile increased over time shown by the curved line.

8a) They can be sure it's a safe following distance by making sure you're concentrating on the three second rule, and if they did it correctly and stopped short, you would have that enough time to react. 8b) The three second rule would not be equally safe because on the highway there aren't as many distracting obstacles like there are on main streets. 9a) (100ft/s)(1/3)=33.3ft 9b) 33.3ft is longer than my classroom 10a) (88ft/s)(.5s)= 44ft 10b) (44ft)/(15automobiles)= about 2.93 automobile lengths 10c) (44ft/s)(.5s)=22ft; 15ft in length is 1.47 automobiles long 10d) (132ft/s)(.5s)= 66ft; 4.4 automobiles long; 11/60 fraction of a football field 11.

September 27, Tuesday Do Now 1. An automobile is traveling at 90 feet per second (60 mph). If the driver's reaction time is .6 seconds, how far does the automobile travel during this time? s=d/t d=s/t d=(90 ft/s)(.6s) d=54 ft. 2. How much further will the car travel if the driver is distracted by texting, so that reaction time is increased to 1.5 seconds? s=d/t d=s/t d= (90 ft/s)(1.5s) d=135 ft 135-54=81 ft 81 ft further September 28, Wednesday Do Now Go-Cart Test Run

Active Physics Plus Part

DistanceTime

Part1 20mi/hr

40mi

2hours

Part2 40mi/hr

40mi

1hour

Whole Trip 80mi Avg V(Vav)=?

3hours

20+40/2=Vav=30mi/hr Vav=Δd/Δt Vav=80mi/Δt wholetrip Vav= 80mi/3hrs=26.67mi/hr Part 1: 20mi/hr=40mi/Δt1 Δt1=2hours Part 2: 40mi/hr=40mi/Δt2 Δt2=1hour Paragraph 1. Make a table of the motion: Part

DistanceTime

Part1 1mi/hr

50mi

50hr

Part2 50mi/hr

50mi

1hr

Whole Trip 100mi 1.96mi/hr

51hrs

2. Calculate: Vav= 100mi/51hrs=1.96mph 3. Explain: It's closer to 1mph because for the most of the time you're traveling 1mph. 80 Mile Trip

100 Mile Trip

Strobe Pictures

October 3rd, Monday Do Now:

Both B and D are saying he started walking out fast but the drops are close together so that means he started walking out slow first. Letter C is the most accurate.

October 4, Tuesday Walk the Graph Graph 1: We had Dana stand in front of the sensor and then when Ashley hopped into the sensor, Dana hopped out.

Graph 2: We did the same process as number 1, but in the opposite order.

Graph 3: For this graph we had Ashley quickly walk towards the sensor, slowly transition into walking backwards, and then quickly walk back to her original spot.

Graph 4: For this graph we had Dana do the same thing as Ashley, except she started walking away from the sensor and then slowly transitioned back towards the sensor.

Graph 5: To make a circle, we repeated graph 3 and 4 and combined them.

Section 4

Section4

Points

WDYSee/Think: /10 Investigate: /20 PhysicsTalk:

/20

PhysicsPlus:

/20

PhysicsToGo:

/20

Wiki

/10

TOTAL POINTS100

October 5th, Wednesday Do Now: What Do You See?

I see two cars at a red traffic light. One car is stopped and one car is speeding through, nearly running over a pedestrian and his dog. The red car has the greater acceleration time. The yellow car has a velocity of 0mi/h. Tangent Line: A Line that touches a curve at only one point

Slope of tangent line on a distance vs. time graph, it represents the instantaneous velocity at any point in time. 10/5/11 LEARNING OUTCOMES In this section we will learn... Measure a change in velocity (acceleration) of a cart on a ramp using a motion detector. Construct graphs of the motion of a cart on a ramp. Define acceleration using words and an equation. Calculate speed, distance, and time using the acceleration equation. Interpret distance-time and velocity-time graphs for different types of motions. 10/5/11 PHYSICS WORDS ACCELERATION: the change in velocity with respect to a change in time VECTOR: a quantity that has both magnitude and direction NEGATIVE ACCELERATION: a decrease in velocity with respect to time. The object can slow down or up with negative numbers. POSITIVE ACCELERATION: an increase in velocity with respect to time. The object can speed up or slow down. TANGENT LINE: straight line that touches a cure at only one point. 10/5/11 CHECKING UP QUESTIONS 1. 2. 3. 4.

Acceleration=change in velocity/change in time; A=Δv/Δt When calculating acceleration you use the SI symbols of m/s over s or (m/s)/s; m/s^2 or m/s^2. It's read as meters per second squared. A vector quantity has direction and size while scalar quantity has size but not direction. Graph on constant velocity and constant acceleration as well as all the other graphs. The two are the last two in the first row.

Screen_shot_2011-10-05_at_4.28.12_PM.png

Screen_shot_2011-10-05_at_4.28.21_PM.png 5. The slope of a velocity v. time graph is a straight constant line.

Investigation: Distance, Velocity, Acceleration 1.) If you were to place the cart at the top of the ramp and release it to freely move down the ramp would it move through the first half of the distance in the same amount of time as the second half of the distance? Why or why not? No, in the second half it would move faster because it would continue to accelerate on the entire ramp, because it is still on a slope. So it will accelerate still after the first half, which would make the speed of the second half faster than the speed of the first half. 2.) Below are four different distance vs time graphs. Copy and paste the graphs with their correct descriptions of motion into your wiki. In one of them the cart does not move- This applies to none of them. In another the car moves at constant velocity- This applies to none of them. In another, the car travels faster at the beginning and slows toward the end.- This is the fourth graph. In another, the car travels slower at the beginning and speeds up.- This is the third graph.

September 7, Friday Do now: Physics Talk Review 1. From a stop light a car accelerates when the light turns green from 0 m/s to 30m/s (60mph) in 5 seconds. What is the acceleration of the car? 2. Name 2 vectors and 2 scalars. What is the difference between a vector and a scalar? Vector has magnitude, size and speed, direction. Scalar only has speed, no direction. Car V. Bus

Speeding Up

Slowing Down

October 11, Wednesday Predicting Graphs

Active Physics Plus

1. A car accelerates from a stop light with acceleration 3 m/s2 from an initial rolling speed of 7 m/s to a speed of 20 m/s. How long does it take the car to do this? Data: a=3m/s Vi=7m/s Vf=20m/s Δt=? Equation: a=Δv/Δt a=Vf-Vi/Δt 3m/s^2=20m/s-7m/s/Δt Δt=20m/s-7m/s/3m/s Δt=13m/s/3m/s=4.33 second 2. If a car accelerates from 7 m/s to with an acceleration of 1.5 m/s2 for 10 seconds what speed is it now going? 1.5m/s^2=Vf-7m/s/10 seconds 15m/s=Vf-7m/s 22m/s=Vf 3. A car accelerates from rest at a stop light to a speed of 20 m/s in 5 sec. a. What is the car’s acceleration? a=20m/s-0m/s/5 seconds a=4m/s^2 b. What distance has the car gone? Data: Vi=? Vf+20m/s a=4m/s^2 t=5 seconds d=1/2at^2+Vit d=1/2(4m/s^2)(5seconds)^2+0 50 meters 4. A car accelerates from rest at a stop light to a speed of 40 m/s in 10 sec. That is an acceleration of 4 m/s2. What distance has the car gone? d=1/2/a(4)(10^2)=200 d=200meters 1. Yes because the object can keep a constant velocity the whole time. 2. No because an object has to be accelerating to have velocity. When there a change in direction, theres no velocity. It still has acceleration because gravity is always pulling on it. 3. No because it depends on which direction they're accelerating. 4. No because they could be traveling or accelerating at different speeds. 5. An accelerating automobile can be taken over by an automobile moving as a constant velocity because that adds the direction it's traveling. A racecar moving at a constant speed at 180mph overtakes someones acceleration on a bike. 6. The speed-limit sign tell how fast you can go up to, not the direction you have to go. There are other sign for velocity. 7. N/A 8. a). (75m/s)/(9s)=8.3m/s^2 c). vi=0m/s(pit stop) vf=75m/s Δt=9s d=? (1/2)(8.33)(9^2)+0=336.15m d). (75m/s)/(8s)=9.375m/s^2;d=300m (d=1/2at^2+vit 9. a). (0.6-4.5)/1.3=-3m/s^2 b). (1/2)(-3)(1.3^2)+(4.5)(1.3)=3.315m c). Δt=1.1s vi=4.5m/s vf=? a=-3m/s^2 a=Δv/Δt -3=(vf)-(4.5m/s)/1.1svf=1.2m/s d). The trial that requires less time sliding (1.1 seconds) would keep her average speed higher so in that case she would get to second base faster 10. a). About 12.5 m/s b). (9-4.5)/(7.5-4.5)=1.5m/s^s c). The acceleration would be constant but objects final velocity would increase linearly 11. a).B b).D d).A e).F f).C

Screen_shot_2011-10-13_at_11.55.50_AM.png 12. a).d between e and f b).b,e c).d d).c,f e). about 1050miles f). at 525miles 13. a). (250m/s)/(30s)=8.3m/s b). (250m/s)/(45s)= 5.56m/s c). a=5.56m/s 5.56=500/x 14. a). 9.8m/s^2=vf-0/4.5sec=44.1m/s b). a=9.8m/s^2=1g vi=0m/s 100m=(1/2)(9.8m/s^2)t^2+0= 4.5sec c). Δt=10 sec vf=? vi=0m/s a=9.8m/s^2--9.8M/S^2=vf-0/10sec=98m/s d). d=(1/2)(9.8m/s^2)(10^2)=490m e). On moon: how fast it goes after 100m-->18.88m/s, how long it takes to go 100m->11.18 sec, how fast it is going after 10 sec-->16m/s, how far it goes in 10 sec--> 80m 16. a). 2m b). 8m c). 18m d). 32m

Active Physics Plus d=1/2at^2+Vi T a= ΔV/ΔT 1.) a= 3m/s Vi= 7m/s Vf=20m/s ΔT= ? a= ΔV/ΔT 3m/s=20m/s - 7m/s/ΔT ΔT=20m/s - 7m/s/3m/s ΔT=13m/s / 3m/s ΔT= 4.33 seconds 2.) Vi= 7m/s a= 1.5 m/s ΔT= 10s 1.5m/s=ΔV/ΔT 1.5m/s= Vf-7/10s 10s(1.5m/s)=Vf-7 15m/s=Vf-7 Vf=22m/s 3a.) a=ΔV/ΔT a= 20/5 a= 4m/s 3b.) d=1/2at^2+Vi T d=1/2(4)(5)^2+0(5) d=1/2(4)(25)+0 d=50m 4.) d=1/2at^2+Vi T d=1/2(4)(10)^2+(0)(1) d=1/2(4)(100) d=200m 5) A car rolls up to a stop light with initial speed 3 m/s and accelerates to 23 m/s in 5 sec. 1. What is the car’s acceleration? 2. What distance has the car gone? 6) A car slows down coming to a red light from a speed of 25 m/s to 0 m/s in 4 sec. 1. What is the car’s acceleration? -6.25m/s^2 2. Why is it negative? Because the car is slowing down 3. How far did it take the car to stop? 1.5 m 7) A car slows down coming to a red light from a speed of 50 m/s to 0 m/s in 8 sec. 1. 2. 3. 4.

What is the car’s acceleration? Why is it negative? How far did it take the car to stop? When the speed was doubled how did the braking distance change.

8) A car accelerates at a rate of -7 m/s2 up to a deer in the road which is 40 m away in 3 seconds from a speed of 21 m/s to a stop. Will the car hit the deer?

Photo_on_2011-10-14_at_12.17.jpg 9) Now the car is moving twice as fast, 42 m/s and slows down with the same acceleration of -7 m/s2. 1. How much time will it take the car to come to a stop? 2. If the car is attempting to avoid a deer which is 80 m away will the car hit the deer? 10) A ferrari whizzes by a cop at a red light at constant velocity of 40 m/s (80 mph), clearly speeding. The cop tries to catch our red light running speeding friend who never notices the cop behind him so continues at simply 80 mph. 1. If the cop car accelerates toward the speeder at a rate of 7 m/s2 how long will it take the cop to catch the speeder. 2. How far will the cop have gone to catch the speeder? 11) A mysterious biker whizzes by a cop at a red light at constant velocity of 50 m/s(100 mph), clearly speeding. The cop tries to catch our red light running speeding friend who never notices the cop behind him so continues at simply 100 mph.

1. 2. How far will the cop have gone to catch the speeder?

Section 5

Section5

Points

WDYSee/Think: /10 Investigate: /20 PhysicsTalk:

/20

PhysicsPlus:

/20

PhysicsToGo:

/20

Wiki

/10

TOTAL POINTS100

Negative Acceleration: Braking Your Automobile October 18th, Tuesday What Do You See/What Do You Think

What Do You See A car breaking really fast because the back tired are coming off the ground. He is stopping because there is a mouse in front ahead. What Do You Think? Reaction time, under the influence, texting, distractions would affect if you will be able to stop. The distance time between you and the mouse and the speed. Measure friction which helps you slow down October 19th, Wednesday Investigation Objective- To determine the effect of initial speed on breaking(stopping) distance. 1st Periods Data Vi(m/s)BrakingDistance(m) .59

2.8m

1.27

11.32m

.94

5.15m

1.06

6.5m

.8

4m

.97

5m

1.23

11m

1.23,/s/.59m/s=2.08 (ratio of Vi's) 11m/2.8m=3.92 (ratio of braking distances) ratio of initial velocities=ratio of braking distances [Vi(2)/Vi(1)]^2=Braking Distance(2)/Braking Distance(1) (x2)^2=x4 (x3)^2=x9 (x4)^2=x16 (x10)^2=x100 Sec5 Investigation Questions 1) If initial velocity is doubled by what factor does braking distance increase. x3 2) If initial velocity is tripled by what factor does braking distance increase. x9 3) If initial velocity is quadrupled (x4) by what factor does braking distance increase. x16 4) Do #8 in book on page77 a. The braking data is located on page 116 on the bottom right. b. No the ratio of the braking distance is 1.7689. The ratio of the braking distance is the ratio of the velocities. c. This data shows that the ratio of the braking distance is equal to the ratio of the initial velocities squared, so it proves our formula even further. 5) If the sports car changed its speed to 30 mph what do you expect its braking distance to be? (Hint: if you half the speed by what factor will the braking distance change?) I would expect the sports cars braking distance to be significantly shorter. I would assume this because a sports car can most certainly maintain a greater speed than 30mph. 6) If the touring sedan changed its speed to 30 mph what do you expect its braking distance to be? The braking distance of the touring sedan at 30 mph would depend upon the average speed of the touring sedan. 7) If each car (sports car and touring sedan) decreased its speed to 15 mph what would their braking distances be? (Hint: if you quarter speed by what factor will the braking distance change?) Physics Words Negative Acceleration- A change in the velocity with respect to time of an object by decreasing speed in the positive direction or increasing speed in the negative direction. Learning Outcomes Plan and carry out an experiment to relate braking distance to initial speed. Determine braking distnace Examine accelerated motion Checking Up Questions pg.82

1. If a vehicle is traveling at a constant speed and then comes to a sudden stop, it has undergone a negative acceleration because it was decreasing speed in a positive direction. 2. You know because the faster the vehicle is going, the farther distance it takes to come to a complete stop. 3. It is used to be more clear in physics.

October 20th, Thursday Honda Civic Stopping Distances Investigation

Honda Civic Stopping Distances 1) Calculate the stopping distances for Kibala’s Honda Civic Initial Velocity Stopping Distance 10 mph

3.4 feet

20 mph

13.6 feet

30 mph

30.75 feet

40 mph

54 feet

50 mph

85 feet

60 mph

123 feet

70 mph

167.4 feet

80 mph

218 feet

90 mph

276.8 feet

100 mph

341.6 feet

[(Vi(2)/Vi(1)]^2=BD(2)/BD(1) (60mph/30mph)^2=123ft/BD(1) 60^2/30^2=123/BD(1) BD(1)=30.75 4) If Initial Velocity is doubled how does stopping distance change? It multiplies by 4 5) If the Initial Velocity is multiplied 4 times how does the stopping distance change? It multiplies by 16 6) If the Initial Velocity is halved how does the Stopping Distance Change? It multiplies by 1/4 7) If the initial Velocity is quartered how does the stopping distance change? It multiplies by 1/16 8) What speed would you need to have a stopping distance of a mile? 393.63 mph

October 21, Friday Direction of Acceleration

October 24th, Monday Active Physics Plus

Physics To Go: p.88-89 #1-8 DUE WEDNESDAY 1.A student measured the braking distance of her automobile and recorded the data in the table. Plot the data on a graph and describe the relationship that exists between initial speed and braking distance. The relationship between the initial speed and the braking distance is that they both gradually increase. However, the braking distance increases by greater intervals than the initial speed does.

2. Below is a graph of the braking distances in relation to initial speed for two automobiles. Compare qualitatively (without using numbers) the braking distances when each automobile is going at a slow speed and then again at a higher speed. Which automobile is safer? Why? How did you determine what “safer” means in this question? Automobile A is safer than automobile B because it doesn't speed up as violently.

3. An automobile is able to stop in 20 m when traveling at 30 mi/h. How much distance will it require to stop when traveling at the following: a) 15 mi/h? (half of 30 mi/h)b)-- 5 meters 60 mi/h? (twice 30 mi/h)--80 meters c) 45 mi/h? (three times 15 mi/h)d)-- 45 meters 75 mi/h? (five times 15 mi/h)--125 meters 4. An automobile traveling at 10 m/s requires a braking distance of 30 m. If the driver requires 0.9 s reaction time, what additional distance will the automobile travel before stopping? What is the total stopping distance, including both the reaction distance and the braking distance? total stopping distance= reaction distance+ braking distance. total stopping distance=Treaction V+30m total stopping distance=.9s(10m.s)+30m total stopping distance=9m+30m total stopping distance=39 meters. 8. Apply what you learned in this section to write a statement explaining the factors that affect stopping distance. The total stopping distance includes the distance you travel during your reaction time, plus the braking distance. What do you know now about stopping that will make you a safe driver? The factors that affect stopping distance are reaction time, speed the vehicle traveling, weather, surrounding environment, and distractions inside the vehicle/with the driver. After reading the section and learning that the total stopping distance includes the distance you travel during your reaction time (plus the braking distance), I can now say that going at a slower speed or following the speed limit and staying aware of my surroundings (to improve my reaction time) will make me a safer driver. Total Stopping Distance TSD=Dreaction + Dbraking TDS=V Tr

October 26th, Wednesday a=negative acceleration, slowing down this is dependent on brakes if you have good brakes you have a big acceleration if you have bad brakes you have a small acceleration if Vi increases then TSD increases

Vi~TSD

if Tr increases

then TSD goes up

Tr~TSD

if a goes up

then TSD goes downTSD~1/a

October 27th, Thursday MINI CHALLENGE PLAN 1. 2. 3. 4.

Paragraph explaining theme/storyline 3 ways you will use equations 3 ways you will use graphs * Emailed to kibala at end of period

Dana, Ashley, Alyssa, Kelsey THEME/STORYLINE Our theme/storyline for the mini challenge is building an amusement park. We’re starting from scratch and attempting to make a roller coaster and bumper cars. This will show speeding up, slowing down, braking distance, and reaction time. We will create these rides through physics equations and rules. We will have to specifically calculate acceleration, distance, and running time of all the rides. We will do all of these things with various equations from active physics plus. 3 WAYS WE WILL USE EQUATIONS 1. D=1/2at^2 2. TSD=dreaction + dbraking 3. A=Δv/Δt 3 WAYS WE WILL US GRAPHS 1. Slowing down graph for roller coaster 2. Speeding up graph for roller coaster 3. Braking distance vs. velocity of bumper cars October 28th, Friday

Calculating Reaction Distance 1. (T reaction(V=D reaction/T reaction(T reaction-2) (T reaction)V=D reaction 2. V=10m/s T reaction=1s T distance=? T distance=10(1) T distance= 10 meters 3. T distance=20(1) T distance=20 meters 4. An increase in speed changes reaction distance because you still have the same reaction time, however if your vehicle is moving faster it will travel further in the same amount of time. Likewise, a decrease in speed would make the reaction distance shorter. Yes, a one second reaction time is large. It could be large because of weather conditions outside, speed of the vehicle, how far away the object is, age of the driver, Calculating Braking Distance 1. Vf^2=Vi^2+2ad braking 0=Vi^2+2ad braking -(Vi)^2=2ad braking d braking=-(Vi)^2/2a 5. a=-11m/s^2 Vf=0 Vi=51m/s 0=51m/s+2(-11m/s)d braking -2601=--22 d braking 118.23m 6. a=-24 0=51^2+2(-24)d braking -2601=-48 d braking 54.2=d braking 7. Better brakes decreases the acceleration. The stopping distance is less with better brakes November 2nd, Wednesday Preparing for the Chapter Challenge 1. Tr=.5 seconds Vi= 11m/s a= -4m/s Dr=? Db=? TSD=? v=d/t 11m/s=d/.5 seconds Db=5.5 m Vf^2=Vi^2+2ad 0=11m/s^2+2(-4m/s)(d) -11m/s^2=2(-4m/s)(d) -11m/s^2/2(-4m/s)=d d=15.125m TSD=Dr+Db TSD=20.625 2. Tr=.5 seconds Vi= 27 m/s a= -4m/s Dr=? Db=? TSD=? V=d/t 27m/s=D/.5 Dr=13.5m Vf^2=Vi^2+2ad 0=27^2 +2(-4m/s)(d) -27^2=2(-4m/s)(d) Db=91.125 TSD=Dr+Db TSD=104.625m 3. Tr=1 seconds Vi= 27 m/s a= -4m/s Dr=? Db=? TSD=? v=d/t 27=d/1 Dr=27m Vf^2=Vi^2+2(a)(d) 0=27^2+2(-4)(d) -27^2=2(-4)(d) Db=91.125 TSD=Db+Dr TSD=118.125m 4. Tr=.5 seconds Vi= 27 m/s a= -2m/s Dr=? Db=? TSD=? v=d/t 27=d/.5 Dr=13.5 Vf^2=Vi^2+2(a)(d) 0=27^2+2(-2)(d) Dr=182.25 TSD=Dr+Db TSD=195.75 5. Make Your Own Assume you have a reaction tim of 1 second including moving your foot form gas to break. You are traveling at 11m/s and your car has a maximum deceleration of -6m/s^2. What is your reaction distance, braking distance, and total stopping distance? Tr=1 seconds Vi= 11 m/s a= -6 m/s Dr=? Db=? TSD=? v=d/t 11=d/1 Dr=11m Vf^2=Vi^2+2(a)(d) 0=11m/s^2(-6)(d) Db=10.083m TSD=Db+Dr TSD= 21.083m 6. Partners Problem Assume you have a reaction time of .8623281 seconds including your foot moving from gas to break. You are traveling at 923.65739 m/s and your car has a breaking distance of -5m/s^2. What is your reaction distance, breaking distance and total stopping distance. Tr=.8623281 seconds Vi= 923.65739 m/s a= -5m/s^2 Dr=? Db=? TSD=? v=d/t 923.65739=d/.8623281 Dr=796.495722m Vf^2=Vi^2+2(a)(d) 0=923.65739^2+2(-5)(d) -923.65739^2=2(-5)(d) Db=85314.29741m TSD=Db+Dr TSD=86110.79313m

Section 6

Section6

Points

WDYSee/Think: /10 Investigate: /20 +8 EC PhysicsTalk:

/20

PhysicsPlus:

/20

PhysicsToGo:

0/20 missing stop and go zone of a real intersection

Wiki

/10

TOTAL POINTS88*.75 = 66/75

November 3rd, Thursday

What Do You See A red car stopping short at a red light but a green car speeding through it. They both seem to be stopping in the middle of the intersection. Red car could have been speeding or the reaction time which made his reaction distance longer. If he was going fast it would have made his reaction distance longer. The green car could have been going through the red light because it is a one way intersection. What Do You Think Is the green car doing something illegal? It is at the intersection while the light is red, this is illegal. This technically states he has run a red light. He might have though it was okay if he was in the intersection when it turned red, but it's still illegal. Go Zone

Stop Zone

November 4th, Friday Investigation- Page 91 #3 and 4 3a. Yes, automobile B will be able to make it through the intersection before the light turns red. 3b. Yes, automobile B is in the go zone because it is able to make it through the yellow light before it turns red. 3c. Yes, because they will all be able to make it through the yellow light before it turns red. 3d. No, because it wont make it through the yellow light before it turns red. This is illegal. 4a. Yes, because it can come to a safe stop before it reaches the red light. If it stops, it will not end up in the middle in the intersection, unsafely. 4b. It is not in the stop zone, so if it tries to stop it will end up in the middle of the intersection. November 7th, Monday input

output

Vi (speedlimit)

Go Zone

Ty(yellow-light time)

Stop Zone

W(width of intersection) A(negative acceleration) Tr(reaction time) Go Zone

Stop Zone

November 8th, Tuesday Part B: Yellow and Light Dilemma 1a. Automobile A: stop Automobile B: go Automobile C: go Automobile D: stop 2a. Automobile E: stop F: stop G: go H: go 3a. J: stop K: go L: stop M: go 4a. The go zone in I has a stop zone and right after, the go zone. The II intersection is overlapping, meaning the go zone is longer and the stop zone is shorter. The third intersection, there is a space between the go and stop zone. The go zone is shorter than usually. Go Zone.Stop Zone Equations Go Zone v=d/t v=d/Ty v=(w+GZ)/Ty vTy=w+GZ vTy-w=GZ where the go zone ends Stop Zone SZ=TSD SZ=Dr+Db SZ=Vi(Tr)+[(Vi)^2/2a] where stop zone begins November 9th, Wednesday Checking Up 1. In this section, the spreadsheet is referred to as a model. What makes it a model? A model is when it has a perfect go zone and stop zone with no overlap or dilemma zone. 2. In your own words, describe what is meant by the Go Zone. The go zone is the zone where it is safe to go through the light. 3. In your own words, describe what is meant by the Stop Zone. The stop zone is the zone where it is safe to brake. 4. Describe what is meant by the Overlap Zone. The overlap zone is the zone where it is safe to brake or go. 5. Describe what is meant by the Dilemma Zone. The dilemma zone is where it is neither safe to go or brake.

Active Physics Plus 1. w=25m Ty=3 sec Vi=20m/s a=-5m/s^2 Tr=.7sec GZ=Vi(Ty)-w GZ=(20m/s)(3sec)-25m GZ=35m SZ=Vi(Tr)-Vi^2/2a SZ=20m/s(.7s)-(20m^2)/2(-5m/s^2) SZ=14m+40m SZ=54m =

2.

Section 7

Section7

Points

WDYSee/Think: /10 Investigate: 0/20 PhysicsTalk:

/20

PhysicsPlus:

/20

PhysicsToGo:

/20

Wiki

/10

TOTAL POINTS60/75

November 14th, Monday Learning outcomes: - Recognize the need for a centripetal force when rounding a curve. - Predict the effect of an inadequate centripetal force. - Relate speed to centripetal force.

What do you see? Car going too fast Almost falling over Smoke coming from the car Sign saying to slow down around the curve What do you think? The sign is indicating to slow down because if your going too fast you can skid out while turning Factors that determine how much you should slow down: weight of the car, weather, speed, condition of tires

November 11, Friday Physics Words Force: a push or a pull Centripetal force: a force directed toward the center to keep an object in a circular path Centripetal acceleration: a change in the direction of the velocity with respect to time Checking Up 1. The direction of the force is toward the center. 2. Centripetal force is what keeps an object moving in a circle. 3. Friction keeps an automobile moving in a circular path on a road. 4. Velocity can change because direction is changing. 5. Acceleration can take place when an object speeds up, slows down, or changes direction. 6. Gravity is the force that keeps Earth moving in a circle around the sun. November 16th, Wednesday Physics To Go 1) A person at the equator travels once around the circumference of Earth in 24 h. The radius of Earth is 6400 km. How fast is the person going? Compute the speed in kilometers per hour (km/h) and in meters per second (m/s). Recall that 1 km is equal to 1000 m. V= 2r / t V = (2)()(6400) /24 V = 1675.5 km/h

V= (2)()(6400000)/24 V= 1675516.1 m/s 2) Earth travels in a circular motion around the Sun. The radius of Earth’s motion is about 1.5 × 108 km. What is the speed of Earth around the Sun? Compute the speed in km/h and m/s. V=2r /t V=2(1.5 x 108) /24 V= 1017.8 /24 V= 42.4 km/h V=2(162000) /24 V=42411.5 m/s V=2r/T = 2(1.5 X108 cm) / 8766 hrs = 1 year= 365.25/1yr X 2.41 ms/1 day= 8766 hrs 3) A fan turns at a rate of 60 revolutions per second. If the tip of the blade is 15 cm from the center, how fast is the tip moving? V= 2r/t V=2(15) / 60 V= 1.6 cm/s 4) Friction can hold an automobile on the road when it is traveling at 20 m/s and the radius of the turn is 15 m. What happens if: a) the curve is tighter? the car can have a smaller maximum speed, it should go slower. If it did not slow down, the car would spin out(ditch) b) the road surface becomes slippery? the car should go slower because there is less friction, could spin out. c) both the curve is tighter and the road is slippery? the car should go slower because there is a better chance or going in the ditch 5) Think about other examples in which objects travel in curved paths, such as the clothes in a spin dryer, or the Moon traveling around Earth. For each example, explain what produces the force that is constantly being applied to the object toward the center of the curve. -objects on curved paths: the friction between the tires/road -clothes in the dryer: push and pull of the dryer -Moon traveling around the Earth: gravity -shot put: hand was the centripetal force keeping it in a circle, push it forward when throwing -The shorter the distance from the center, the faster the block can go without falling off 7) Explain the following statement: “The driver may turn the wheels but it is the road that turns the automobile.” - The driver ultimately decides where the car goes because they control whether or not to turn the wheel and in which direction. However, the direction of the road influences the driver's decision of where to move the wheel. If the road curves, then the driver will follow the road. 8) A jet pilot in level flight at a constant speed of 270 m/s (600 mi/h) Plusrolls the airplane on its side and executes a tight circular turn that has a radius of 1000 m. What is the pilot’s centripetal acceleration? Draw a sketch of the acceleration’s direction relative to the ground. a = v2/r a = (270)2/1000 a = 72.9 m/s2

9) Below you will find alternate explanations of the same event given by a person who was not wearing a seat belt when an automobile went around a sharp curve. “I was sitting near the middle of the front seat when the automobile turned sharply to the left. A force made my body slide across the seat toward the right, outward from the center of the curve, and then my right shoulder slammed against the door on the passenger side of the automobile.” “I was sitting near the middle of the front seat when the automobile turned sharply to the left. My body kept going in a straight line while, at the same time due to insufficient friction, the seat slid to the left beneath me, until the door on the passenger side of the automobile had moved far enough to the left to exert a centripetal force against my right shoulder.” Are both explanations correct? Explain your answer in terms of both explanations. -The first explanation is correct because the quick change in direction and acceleration made the person's body jerk sharply right, especially because they did not have a seatbelt on to constrain the force. The second explanation is not correct because the seat cannot slide, only the person in the seat. 10) Race cars can make turns at 150 mi/h. What forces act on a race car as it moves along a circular path at constant speed on a flat, horizontal surface? -Centripetal force keeps the race car going around the curved track and friction keeps the tires flat on the ground. 11) Why are highway curves that have radii that decrease as you go into them especially dangerous? In other words, curves that start out as gentle turns but become tighter and tighter as you get into them. -They are especially dangerous because as you continue turning, your velocity increases and it becomes harder to continue making a sharp turn. 12) In the United States, vehicles drive on the right-hand side of a two-lane road. If the curve bends to the right and you lose traction in the turn, would you end up in the ditch on your side of the road, or into the lane of oncoming traffic? What if the curve bends to the left? -If the curved bends right and the driver could not make it, the car would end up in the left lane with oncoming traffic. If the curve bends left and the driver cannot make it, the car would end up in a ditch on their side of the road. 13) Write a few sentences telling your parents that you know how to apply the physics from this section to drive safely around curves. You should include information about why you need to slow down around curves in rainy or icy weather. -drivers should always go slowly around curves because it is easy to end up on the side of the road or in the other lane. This is especially true in bad weather where the road is icy because there is a loss of friction between the tires and the road. Active Physics Plus Fc = mv2/r *(newtons)=(kg)(m/s)2/ (m)= kg(m^2/s^2)/(m)*(1/m)/(1/m) Ac =v2/r 1) A car makes a left turn at a small intersection with turning radius 10 m. The mass of their car is 2000 kg. The pavement provides a frictional force of 13,720 N. What maximum speed can the car make the turn with? 8.3 m/s Fc = mv 2/r (10m)(1370N) = 20000kg) (v 2) 20000kg square root of 686 = V 2 V= 8. 3 m/s 2) Now the pavement is wet and made on the same turning radius and with the same car. The wet pavement causes the frictional force to cut in half. What maximum speed can the car make the turn with? 5.6 m/s Fc= mv2/r 6860=2000(v2) /10 68600= 2000v2 *divide by 2000 to get V2 alone 34.3=V2 *square root it v=5.86 newtons 3) What minimum radius can a car make a turn with if it is traveling at 10 m/s, has a mass of 3000 kg and has a provided frictional force of 20,580 N? What can the car do to make the turn at an even sharper radius? 14.6 m Fc= mv2/r 20, 580 = 3000(10) / r 20,580 = 30000/r r= 6.86

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