Lab 3 - Velocity and Acceleration

Transcription

1 Lab 3 Velocity and Acceleration L3-1 Name Date Partners Name Date Partners Lab 3 - Velocity and Acceleration LAB 3 - VELOCITY AND ACCELERATION L03-1 A cheetah can accelerate from 0 to 50 miles per hour in 6.4 seconds. A cheetah can accelerate from 0 to 50 miles Encyclopedia per hourof inthe 6.4Animal seconds. World A Jaguar can accelerate from 0 to 50 miles per Encyclopedia hour in 6.1 seconds. of the Animal World World Cars OBJECTIVES A Jaguar can accelerate from 0 to 50 miles per hour in 6.1 seconds. To understand the meaning of acceleration, its magnitude, and its World direction. Cars To discover the relationship between velocity and acceleration graphs. OBJECTIVES To learn how to find average acceleration from acceleration, velocity and position graphs. To understand the meaning of acceleration, its magnitude, and its direction. OVERVIEW To discover the relationship between velocity and acceleration graphs. In the previous labs, you looked at position time and velocity time graphs of the To learn how to find average acceleration from acceleration, velocity and position graphs. motion of your body and a cart at a constant velocity. You also looked at the acceleration time graph of the cart. The data for the graphs were collected using a OVERVIEW motion detector. Your goal in this lab is to learn how to describe various kinds of motion In the previous in more labs, detail. you looked at position time and velocity time graphs of the motion of your body and a cart at a constant velocity. You also looked at the acceleration time graph of You the cart. have The probably data for the realized graphs that were collected a velocity time using a motion graph detector. is easier Yourto goal use in this than laba is position time to learn how to describe graph when various you kinds want ofto motion know inhow morefast detail. and in what direction you are moving at each instant in time as you walk (even though you can calculate this You have probably realized that a velocity time graph is easier to use than a position time information from a position time graph). graph when you want to know how fast and in what direction you are moving at each instant in It time is not as you enough walk (even when though studying you can motion calculate in physics this information to simply fromsay a position time that the object graph). is moving toward the right or it is standing still. When the velocity of an object is It is not enough when studying motion in physics to simply say that the object is moving toward changing, it is also important to describe how it is changing. The rate of change of the right or it is standing still. When the velocity of an object is changing, it is also important velocity to describe with how respect it is changing. to time is The known rate of as change the acceleration. of velocity with respect to time is known as To theget acceleration. a feeling for acceleration, it is helpful to create and learn to interpret velocity time To get and a feeling acceleration time for acceleration, graphs it is helpful for simple to create motions and learn of toa interpret cart on velocity time a smooth, level and ramp. acceleration time You will be graphs observing for simple the cart motions with of the a cart motion on adetector smooth, level as it ramp. moves You with will its be velocity observing changing the cart at with a constant the motion rate. detector as it moves with its velocity changing at a constant rate.

2 L3-2 Lab 3 Velocity and Acceleration INVESTIGATION 1: Velocity and Acceleration Graphs In this investigation you will be asked to predict and observe the shapes of velocity time and acceleration time graphs of a cart moving along a smooth, level ramp. You will need the following materials: L03-2 Lab 3 - Velocity & Acceleration motion detector motion cart INVESTIGATION 1: VELOCITY AND ACCELERATION GRAPHS motion track In this investigation you will be asked to predict and observe the shapes of velocity time level and acceleration time graphs of a cart moving along a smooth, level ramp. You fanwill unitneed attachment the following with batteries materials: and dummy cell motion detector motion cart small screwdriver (to help remove batteries) motion track level Activity fan 1-1: unit Moving attachment Away with and batteries Speeding and Up dummy cell small screwdriver (to help remove batteries) In this Activity activity1-1: youmoving will lookaway at velocity time and Speeding and acceleration time Up graphs of the motion of a cart, and you will be able to see how these two representations of the motion are related to each other In when this activity the cart isyou speeding will look up at velocity time and acceleration time graphs of the motion of a cart, and you will be able to see how these two representations of the This motion could are be done related by to moving each other cart when with the your cart hand, is speeding but it is up difficult to get a smoothly changing velocity in this way. Instead you will use a fan or propeller driven by an electric motor to accelerate This could the be cart. done by moving the cart with your hand, but it is difficult to get a smoothly changing velocity in this way. Instead you will use a fan or propeller driven 1. by Make an electric sure the motor fan switch to accelerate is off, and the then cart. place three batteries and the dummy cell in the 1. battery Make compartment sure the fan of switch the fanis unit. off, and Placethen extra place battery three batteries in one of the and clips the dummy on top ofcell the in fan the unit. battery [We compartment do this to keep the of the fan cart fan mass unit. constant Place the throughout extra battery the investigation.] one of the clips on top of the fan unit. [We do this to keep the fan cart mass constant throughout the investigation.] NOTE: To preserve the batteries, switch on the fan unit only when you are making measurements. To preserve the batteries, switch on the fan unit only when you are making Note: measurements. 2. Set the cart on the ramp, with the fan unit and motion detector as shown below. The 2. motion Set the detector cart on should the ramp, be clipped with tothe end fan of unit theand rack, motion not simply detector restingas onshown its surface. below. Verify The motion that the detector ramp is level should andbe that clipped the fan to blade the does end not of the extend rack, beyond not simply the endresting of the on cart its facing surface. the motion Verify detector. that the [If ramp it does, is level the motion and that detector the may fan collect blade does bad data not from extend the beyond rotatingthe blade.] end of the cart facing the motion detector. [If it does, the motion detector may collect bad data from the rotating blade.] 3. Put the switch on the motion detector to narrow beam. 3. Put the switch on the motion detector to narrow beam. Motion Detector End Stop >20 cm -1 Note: The software is configured to treat movement away from the detector as being in the positive direction. 4. Open the experiment file called L Speeding Up.

3 Lab 3 Velocity and Acceleration L3-3 NOTE: The software is configured to treat movement away from the detector as being in the positive direction. 4. Open the experiment file called L Speeding Up. 5. Start graphing and use the position graph to make sure that the detector can see the cart all the way to the end of the ramp. You may need to tilt the detector up or down slightly. Clear all data runs before moving on. 6. With the back of the cart around 20 cm away from the sensor, hold the cart from the side, switch the fan unit on and begin graphing. When you hear the clicks of the motion detector, release the cart from rest. Do not put your hand between the cart and the detector. Be sure to stop the cart before it hits the end. Stop the program from taking data if it has not already shut off. Turn off the fan unit. 7. Repeat, if necessary, until you get a nice set of graphs. 8. Print out one set of graphs for your group report. Do not erase your data. Remember what data set this is. Label these graphs Speeding Up 1. Question 1-1: What feature of your velocity graph signifies that the motion was away from the motion detector? Question 1-2: What feature of your velocity graph signifies that the cart was speeding up? How would a graph of motion with a constant velocity differ? Question 1-3: During the time that the cart is speeding up, is the acceleration positive or negative? In other words, how does speeding up while moving away from the detector result in this sign of acceleration? [Hint: Remember that acceleration is the rate of change of velocity. Look at how the velocity is changing.]

4 L3-4 Lab 3 Velocity and Acceleration Question 1-4: How does the acceleration change in time as the cart speeds up? Is this what you expect based on the velocity graph? Explain. Activity 1-2: Speeding Up More Prediction 1-1: Suppose that you accelerate the cart at a faster rate. How would your velocity and acceleration graphs be different? Sketch your predictions with different color lines on the graphs using create prediction data set tool of the software. Ask you TA if you are not familiar with the tool. 1. Test your predictions. Make velocity and acceleration graphs with all four of the batteries in the battery compartment. [You may need to use the small screwdriver to pry out the dummy cell.] Place the dummy cell in one of the clips on top of the fan cart. Catch the cart before it hits the end stop! Remember to switch the fan unit on only when making measurements. 2. Repeat as necessary to get nice graphs. When you get a nice set of graphs, do not erase them and remember which data set they are for use later. 3. Print one set of graphs for your group report. Label these graphs Speeding Up 2. Question 1-5: Did the shapes of your velocity and acceleration graphs agree with your predictions? How is the magnitude (size) of acceleration represented on a velocity time graph?

5 Lab 3 Velocity and Acceleration L3-5 INVESTIGATION 2: Measuring Acceleration In this investigation you will examine the motion of a cart accelerated along a level surface by a battery driven fan more quantitatively. This analysis will be quantitative in the sense that your results will consist of numbers. You will determine the cart s acceleration from your velocity time graph and compare it to the acceleration read from the acceleration time graph. NOTE: You will need the data you took in Investigation 1. Activity 2-1: Velocity and Acceleration of a Cart That Is Speeding Up 1. Display the data from Activity 1-1. Comment: Average acceleration during a particular time interval is defined as the average rate of change of velocity with respect to time that is, the change in velocity divided by the change in time. By definition, the rate of change of a quantity graphed with respect to time is also the slope of the curve. Thus, the (average) slope of an object s velocity-time graph is also the (average) acceleration of the object. 2. We want to find the average acceleration of the cart from your velocity graph. [Do not yet use a fit or any statistical tools.] Look for a reasonably smooth region of the acceleration graph. Only use values from the portion of the graph after the cart was released and before the cart was stopped. NOTE: Use this same time span for each of the following analysis activities. One way to achieve it is to select an area of interest from the same starting point and adjust the highlighted area on all graphs to be the same size. 3. Click on the velocity graph and use the Coordinate(Smart) Tool, to read the velocity and time coordinates for the endpoints of your selected time span. Point 1 Point 2 Time (s) Velocity (m/s) 4. Calculate the change in velocity between points 1 and 2. Also calculate the corresponding change in time (time interval). Divide the change in velocity by the change in time. This is the average acceleration. Show your calculations below. Speeding up Change in velocity (m/s) Time interval (s)

6 L3-6 Lab 3 Velocity and Acceleration Average acceleration: m/s 2 Question 2-1: Is the acceleration positive or negative? Discuss. Is this what you expected? Question 2-2: What is your best estimate of the uncertainty (in other words, your probable error) in this determination of the magnitude of the average acceleration? [Consider the following: Have you enough information to give a meaningful answer?] Justify your answer. Activity 2-2: Using Statistics and Fit to Find the Average Acceleration In Activity 2-1 you found the value of the average acceleration for a motion with steadily increasing velocity from the slope of the velocity time graph. The statistics feature in the software allows you to find the average (mean) value directly from the acceleration time graph. The fit routine allows you to find the line that best fits your velocity time graph from Activity 2-1. The equation of this line includes a value for the slope. 1. Use the statistics feature to determine the mean value of acceleration. First select the portion of the acceleration time graph for which you want to find the mean value. (Remember to use precisely the same time region that you used in Activity 2-1.) Average acceleration: m/s 2 Sample standard deviation of acceleration: m/s 2 Number of measurements in sample: Question 2-3: What is your estimate of the uncertainty and the relative uncertainty in this determination of the magnitude of the average acceleration? Show your work. [Hint: Look in Appendix C for standard error in the mean.] Average acceleration: ± m/s 2

7 Lab 3 Velocity and Acceleration L Use the fit routine to try a linear fit to the velocity time graph (y = mx +b, where yis the velocity and x is the time). Select the same portion of the velocity time graph as before. Record the fit parameters and their associated uncertainties: m: m/s 2 σ m : m/s 2 b: m/s σ b : m/s Question 2-4: What are the physical meanings of the parameters m and b? Question 2-5: From this fit, what is the magnitude of the average acceleration? Question 2-6: What is your estimate of the uncertainty and the relative uncertainty in this determination of the magnitude of the average acceleration? Show your work. Average acceleration: ± m/s 2 Recall that for uniform linear acceleration a, the position x as a function of time t is given by: x(t) = x 0 + v 0 t at2 where x 0 is the initial position and v 0 is the initial velocity. 3. Now use the fit routine to try a quadratic fit to the position-time graph (y = Ax 2 + Bx +C; here y is the position; x is still the time). Remember to use precisely the same time region that you used in Activity2-1. Record the fit parameters and their associated uncertainties: A: m/s 2 σ A : m/s 2 B: m/s σ B : m/s C: m σ C : m

8 L3-8 Lab 3 Velocity and Acceleration Question 2-7: What are the physical meanings of the parameters A, B and C? What, then, is the magnitude of the average acceleration? Question 2-8: What is your estimate of the uncertainty and the relative uncertainty in this determination of the magnitude of the average acceleration? Show your work. Average acceleration: ± m/s 2 4. List below in Table 3.1 the method, the acceleration found, and its uncertainty for each method of determining the acceleration. Method Acceleration a (m/s 2 ) End points of velocity & time Using statistics Relative Uncertainty σ a /a Using linear fit of velocity Quadratic fit of position Table 3.1: Question 2-9: How do the four values of acceleration that you found here and in Activity2-1 agree with each other? Which one(s) do you trust the most? Explain. INVESTIGATION 3: Slowing Down and Speeding Up In this investigation you will look at a cart moving along a level surface and slowing down. A car being driven down a road and brought to rest when the brakes are applied is a good example of this type of motion. You will also examine the motion of the cart toward the motion detector and speeding up.

9 Lab 3 Velocity and Acceleration L3-9 INVESTIGATION 3: SLOWING DOWN AND SPEEDING UP In both cases, we are interested in how velocity and acceleration change over time. That is, In this investigation you will look at a cart moving along a level surface and slowing we are interested in the shapes of the velocity time and acceleration time graphs (and their down. A car being driven down a road and brought to rest when the brakes are applied relationship to each other), as well as the vectors representing velocity and acceleration. is a good example of this type of motion. You will need the following materials: You will also examine the motion of the cart toward the motion detector and speeding up. motion detector In both cases, we are interested in how velocity and acceleration change over time. That motion is, we cart are interested in the shapes of the velocity time and acceleration time graphs (and their relationship to each other), as well as the vectors representing motion track velocity and acceleration. level You will need the following materials: fan motion unit attachment detector with batteries motion cart motion track level Activity fan 3-1: unit Moving attachment Away with and batteries Slowing Down Activity 3-1: Moving Away and Slowing Down In this activity you will look at the velocity and acceleration graphs of the cart moving away from In the this motion activity detector you will andlook slowing at the down. velocity and acceleration graphs of the cart moving away from the motion detector and slowing down. 1. The cart, ramp, and and motion detector should should be be set set up up as as in in Investigation Use Use the the maximum number number of batteries. of batteries. The fan The should fan should be pushing be pushing the cart toward the cart thetoward motionthe detector. motion detector. >20 cm Prediction 3-1: If you give the cart a short push away from the motion detector and release it, will the acceleration be positive, negative, or zero after it is released? Enter a +, -, or 0 in the appropriate cell of Table 3.2 below. [We ll fill in the rest of the table as we go.]. Scenario PHYS 1429, Spring 2011 Object is slowing down and moving away. Is acceleration + (positive), - (negative) or 0 (zero)? Prediction Modified from P. Laws, D. Observation Sokoloff, R. Thornton Object is speeding up and moving toward. Object is slowing down and moving toward. Object is speeding up and moving away. Table 3.2: General rule for sign of Acceleration Prediction 3-2: Sketch your predictions for the velocity time and acceleration time graphs on the axes below.

10 Prediction L : Sketch your predictions for the velocity time Lab 3 Velocity and and acceleration Acceleration time graphs on the axes below. + PREDICTION Velocity (m/s) 0 Acceleration (m/s 2 ) Time (s) Now we will test your predictions. Now we will test your predictions. 2. Open the experiment file called L Slowing Down. 2. Open the experiment file called L Slowing Down. 3. Turn the fan unit on. Begin graphing with the back of the cart around 20 cm away 3. from Turnthe thesensor. fan unitwhen on. Begin you graphing begin to with hear the back clicks of from the cart the around motion 20 detector, cm away from give the the cart sensor. a gentle When push youaway beginfrom to hear the the detector clicks so fromthat theit motion comes detector, to a stop give near the the cart end a of gentle the ramp. push away [Be from sure the that detector your so hand thatis it comes not between to a stopthe nearcart the end and of thedetector.] ramp. [Be Catch sure that the cart your before hand is it not stops between do the not cart let and it return the detector.] toward Catch the motion the cart before detector and it stops turn dothe not fan letunit return off immediately toward the motion to save detector and the batteries. turn the fan unit off immediately to save the batteries. 4. You may have to try a few times to get a good run. Don t forget to change the axes if this PHYS 1429, Spring 2011 will make your graphs easier to read. 5. Leave your data so that the graphs are persistently displayed on the screen. 6. Print out one set of graphs for your group and include them in your report. Label your graphs with A when you started pushing. B when you stopped pushing. C the time span where only the force of the fan is acting on the cart. D when you stopped the cart. Question 3-1: Did the shapes of your velocity and acceleration graphs agree with your predictions? How can you tell the sign of the acceleration from a velocity time graph?

11 Lab 3 Velocity and Acceleration L3-11 Question 3-2: What is the sign of the acceleration (which indicates its direction)? Fill in the corresponding cell in Table 3.2. Is it what you predicted? How does slowing down while moving away from the detector result in this sign of acceleration? [Hint: Remember L03-10 Lab 3 - Velocity & Acceleration that acceleration is the rate of change of velocity with respect to time. Look at how the velocity is changing.] Prediction 3-1: If you give the cart a short push away from the motion detector and release it, will the acceleration be positive, negative, or zero after it is released? Enter a +, -, or 0 in the appropriate cell of Table 3-1 below. [We ll fill in the rest of the table as we go.]. Table 3-1 General rule for sign of Acceleration Prediction 3-3: Based on your observations so far Is in acceleration this lab, fill+ in(positive), the rest of the prediction cells in Table 3.2. Scenario - (negative) or 0 (zero)? Prediction Observation Object is slowing down and moving away. Object is speeding up and moving toward. Object is slowing down and moving toward. Activity 3-2: Moving Toward and Speeding Up Object is speeding up and moving away. Prediction 3-4: Suppose now that you start with the cart at the far end of the ramp, and let the fan push it toward the motion detector. Sketch your predictions for the velocity time Prediction and acceleration time 3-2: Sketch graphs your predictions the axes that for follow. the velocity time and acceleration time graphs on the axes below. + PREDICTION Velocity (m/s) 0 Acceleration (m/s 2 ) Time (s) Now we will test your predictions. Test your predictions. 2. Open the experiment file called L Slowing Down. 3. Turn 1. First, the fan clear unit any on. previous Begin graphs. graphing Graph with the the cartback moving of the toward cart the around detector 20 and cm speeding away from up: the Do sensor. not letwhen the cart you hitbegin the motion to hear detector. the clicks Turn from the fan the unit motion on, and detector, when you give hear the cart the a clicks gentle from push theaway motionfrom detector, the detector release the so cart that from it comes rest from to a the stop farnear end of the theend ramp. of the ramp. [Be sure that your hand is not between the cart and the detector.] Catch the cart before it stops do not let it return toward the motion detector and University turn the fan of Virginia unit off Physics immediately Department to save the batteries.

12 L3-12 Lab 3 Velocity and Acceleration Be sure that your hand is not between the cart and the detector. Catch the cart when it gets to within about 50 cm of the motion sensor and turn the fan unit off immediately. 2. Print out one set of graphs for your group. Label these graphs as Speeding Up Moving Toward. Label your graphs with B when you released the cart. C the time span where only the force of the fan is acting on the cart. D when you stopped the cart. Question 3-3: How does your velocity graph show that the cart was moving toward the detector? Question 3-4: During the time that the cart was speeding up, is the acceleration positive or negative? Fill in the corresponding observation cell in Table 3.2. Does this agree with your prediction? Explain how speeding up while moving toward the detector results in this sign of acceleration. [Hint: Look at how the velocity is changing.] Question 3-5: When an object is speeding up, what must be the direction of the acceleration relative to the direction of object s velocity? [Are they in the same or different directions?] Explain. Question 3-6: There is one more possible combination of velocity and acceleration directions for the cart: moving toward the detector and slowing down. Think about your prediction from Table 3-1 to see if you want to change it. Explain why the acceleration should have this direction and this sign in terms of the sign of the velocity and how the velocity is changing.

13 Lab 3 Velocity and Acceleration L3-13 Activity 3-3: Moving Toward and Slowing Down Motion Detector End Stop >20 cm -1 L03-14 Lab 3 - Velocity & Acceleration 1. Clear any previous graphs. Graph the motion of the cart moving toward the detector and slowing down: Do not let the cart hit the motion detector. Position the cart near the 1. Clear any previous graphs. Graph the motion of the cart moving toward the end stop and with the fan again facing the motion sensor. Turn the fan unit on, and when detector and slowing down: Do not let the cart hit the motion detector. Position you hear the clicks from the motion detector, give the cart a gentle push away towards the the cart near the end stop and with the fan again facing the motion sensor. Turn the detector so that it travels at least 1 m before stopping. Catch the cart before it stops and fan turn unit the on, fan and unit when off immediately. you hear the clicks from the motion detector, give the cart a gentle push away towards the detector so that it travels at least 1 m before stopping. 2. Print out Catch one set the for cart you before group. it Label stops as and Slowing turn the Down fan unit Moving off immediately. Toward. Label your graphs with 2. Print out one set for you group. Label as Slowing Down Moving Toward. Label your A when graphs youwith started pushing. A when B when you you started stopped pushing. pushing. B when C the you time stopped span where pushing. only the force of the fan is acting on the cart. D when the cart stopped moving. C the time span where only the force of the fan is acting on the cart. 3. Based D when onthe your cart results stopped in this moving. lab, fill in the rest of Table 3.2. [See Investigation 1 for Moving away and speeding up.] 3. Based on your results in this lab, fill in the rest of Table 3-1. [See Investigation 1 for Moving away and speeding up.] INVESTIGATION 4: Reversing Direction INVESTIGATION 4: REVERSING DIRECTION Activity 4-1: Reversing Direction Activity 4-1: Reversing Direction In Inthis activity you will look at at what what happens when when the cart the slows cart slows down, down, reverses reverses its direction its direction and thenand speeds then upspeeds in the opposite up in the direction. opposite How direction. does the velocity How does change the with velocity time? change What is with the cart s time? acceleration? What is the cart s acceleration? The setup should be as shown below. [The [The fan fan unit unit should should have the have maximum the maximum number number of batter- of batteries.] 20 cm! Prediction 4-1: Imagine that you start the the fan fan and and give give the cart the acart pusha away push from away the from mo-the motion detector. It moves It moves away, away, slows slows down, down, reverses reverses direction, direction, and thenand moves then back moves toward back toward the detector. the detector. For each part For ofeach the motion away part of the from motion away the detector, from at the the turning detector, point, and at the turning towardpoint, the detector indicate and toward the indetector indicate the table below whether in the the table velocity below and whether acceleration the velocity will and be acceleration positive, zero, will or negative. be positive, zero, or negative. Velocity Moving away At the turning point Moving toward

14 Scenario - (negative) or 0 (zero)? L3-14 Prediction Lab 3 Velocity Observation and Acceleration Object is slowing down and moving away. Moving Object is speeding up and moving away toward. Object is slowing Velocity down and moving toward. Acceleration Object is speeding up and moving away. At the turning point Moving toward Prediction 4-2: On the axes that follow sketch your predictions of the velocity time and Prediction acceleration time 3-2: Sketch graphsyour of this predictions entire motion. for the velocity time and acceleration time graphs on the axes below. + PREDICTION Velocity (m/s) 0 Acceleration (m/s 2 ) Time (s) Now we will test your predictions. Test your predictions. 2. Open the experiment file called L Slowing Down. 3. Turn 1. Set the up fan tounit graph on. velocity Begin and graphing acceleration. with the [Youback should of the stillcart be using around the20 experiment cm away file from L the sensor. Slowing When Down.] you begin to hear the clicks from the motion detector, give the cart a gentle push away from the detector so that it comes to a stop near the end 2. Turn on the fan unit, and begin graphing with the back of the cart around 20 cm from the of the ramp. [Be sure that your hand is not between the cart and the detector.] sensor. When you begin to hear the clicks from the motion detector, give the cart a gentle Catch the cart before it stops do not let it return toward the motion detector and push away from the detector so that it travels at least 1 m, slows down, and then reverses turn the fan unit off immediately to save the batteries. its direction and moves toward the detector. Catch the cart at least 20 cm from the motion detector and then stop taking data. [Push and stop the cart with your hand on its side. Be sure that your hand is not between the cart and the detector.] Turn off the fan. PHYS 1429, Spring You may have to try a few times to get a good round trip. Don t forget to change the scales if this will make your graphs clearer. 4. Print one set of graphs for your group after you obtain a good round trip. 5. Label both your prediction graph and your final printed graph with A where the cart started being pushed. B where the push ended (where your hand left the cart). C where the cart reached its turning point (and was about to reverse direction). D where you began to stop the cart.

15 Lab 3 Velocity and Acceleration L3-15 E where was once again at rest (fully stopped). Question 4-1: Did the cart stop at its turning point? [Hint: Look at the velocity graph. What was the velocity of the cart at its turning point?] Does this agree with your prediction? How much time did it spend at the turning point velocity before it started back toward the detector? Question 4-2: According to your acceleration graph, what is the acceleration at the instant the cart reached its turning point? Is it positive, negative, or zero? Is it significantly different from the acceleration during the rest of the motion? Does this agree with your prediction? Question 4-3: Use the best quantitative method from Investigation 2 to determine if acceleration before and after the turning point are the same? Discuss the difference (if any) between the acceleration while the cart is going away from the motion detector and while it is going back towards it. Activity 4-2: Sign of Push and Stop Find and mark on your acceleration graphs for Activity 4-1 the time intervals when you pushed the cart to start it moving and when you stopped it. Question 4-4: What is the sign of the acceleration for each of these intervals? Explain why the acceleration has this sign in each case. Pushing: Stopping:

16 point, and then moves back down toward your hand. Assuming that upward is the positive L3-16 direction, indicate in the table that follows whether Lab 3 Velocity the velocity and Acceleration and acceleration is positive, zero, or negative during each of the three parts of the motion. Moving up after release At highest point Moving down Velocity Challenge: You throw a ball up into the air. It moves upward, reaches its highest point, and then moves back down toward your hand. Assuming that upward Acceleration is the positive direction, indicate in the table that follows whether the velocity and acceleration is positive, zero, or negative during each of the three parts of the motion. Moving up At highest Moving Question 4-5: In what ways is after the motion releaseof the point ball similar down to the motion of the cart that you just observed? Velocity What causes the ball to accelerate? Acceleration Question 4-5: In what ways is the motion of the ball similar to the motion of the cart that you just observed? What causes the ball to accelerate? Please clean up your lab area PHYS 1429, Spring 2011