Studio Physics I
Introduction to Motion in One Dimension
Here are a few comments to help you in all the lab work that you do in this course. Please read these carefully.
A) Record all answers to questions on your own sheet of paper. Questions are clearly labeled,
“Question (A)” “Question (B)” etc.
B)
“Sketch” means that you need to record the shape and most important characteristics of the graph. You do not need numerical values. However, it should be clear where values are zero, positive and negative.
C) When you record graphical data, you should always record ONLY the RELEVANT
DATA. You should not record any portion of the graph that corresponds to something that happened before or after the period of time that interests you.
D) The motion detectors record the position, velocity and acceleration of WHATEVER object is closest to it. This means that it will record your hand, book bag or whatever-rather than the object that you want it to track-if you are not careful.
E) Do not try to detect objects that are closer than 0.5 meters from the detector. The motion detectors go crazy and record complete nonsense.
F) Slow and/or gentle pushes and pulls almost always get you better data than fast and/or hard.
G) The carts and tracks that we use have reasonably low frictional forces between them. This means that if you give a cart a good push, it will keep moving at a reasonably constant speed.
(It will not slow down much.)
H)
Make sure your track is level. We have a carpenter’s level for this purpose.
I) You can hurt yourself with the fans. PLEASE BE VERY CAREFUL!!
ACTIVITY: Position, Velocity, and Acceleration Graphs
1) You have a cart, a motion detector, and a fan. The system can be set up for constant velocity
(figure 1) or constant acceleration (figure 2).
Figure 1: Constant Velocity . Start the cart 0.5 meters away from the motion detector. Give the cart a quick, medium push away from the motion detector and let it go. Catch the cart when it gets to the end of the track. The track is essentially frictionless so no forces should act on the cart, meaning acceleration is zero.
Push and release--keep hand out of way of motion detector
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 2004 Bedrosian

Figure 2: Constant Acceleration . Mount the fan on the cart so that it is secure. Start the cart 0.5 meters away from the motion detector. Do not give the cart a push to get it moving.
Rather, turn on the fan and orient it so that the cart moves way from the motion detector speeding up as it goes. Since the fan exerts a constant force on a constant mass, the acceleration of the cart is constant.
2)
Open the software program “ LoggerPro” (in the “Vernier Software” folder). You open the
file you will need for the first part of this activity by going File, Open, <Your Physics1
Data Folder>, L01A3-1 (Vel from Pos).mbl Set up the motion detector, track, and cart as desired to answer the questions below. . Keep in mind that you have to keep your hands, laptops, books, and everything else positioned so that the cart is always the closest thing to the motion detector. When you feel that you are ready to collect actual data, set up the equipment and then click the “collect” button at the top of the screen. There is a 1-2 second delay between doing this and the start of data collection. When you hear the motion detector start to make a clicking noise, give the cart a push.
3) For Constant Velocity (as in Figure 1) : a) Make measurements with LoggerPro as described above in Figure 1. b) Sketch graphs of displacement (position) and velocity versus time. c) Displacement is distance from the motion detector. Is it increasing or decreasing? d) Velocity is the time derivative of displacement. Is it positive or negative? e) How does your answer to (b) relate to your answer for (c)? f) What would the graphs look like under ideal conditions with no friction?
4) For Constant Acceleration (as in Figure 2) :
You open the file you will need for the rest of the activity by going File, Open, <Your Physics1
Data Folder> , L02A3-1 (Slowing Down).mbl You do not want to save your old file.
a) Make measurements with LoggerPro as described above in Figure 2. b) Sketch graphs of velocity and acceleration. c) What would the graphs look like under ideal conditions with constant acceleration? d) The cart should be speeding up. How can you tell from the velocity graph? e) Suppose you had only the acceleration graph (ideal) but you did not know the initial velocity. Could you correctly predict whether the cart was speeding up or slowing down?
(You might want to come back to this question after doing the exercise.)
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 2004 Bedrosian

EXERCISE: Working with Position, Velocity, and Acceleration Graphs
In this exercise, you are given a graph of velocity of a cart versus time (shown below) and you will need to calculate graphs of displacement and acceleration versus time. You will also be asked to identify the time intervals during which the cart is speeding up and slowing down. You can assume that the displacement = zero at time = zero. v (m/s)
+1 t (sec)
-1
0
2 4 6 8 10
5) During what time interval(s), if any, is the cart speeding up? Slowing down? Hint: Try sketching a graph of absolute value of velocity (speed) versus time.
6) Draw (not sketch) a graph of acceleration versus time. Your graph should include units and clearly show the shape of the curve(s) that you draw.
7) Draw (not sketch) a graph of displacement versus time. Your graph should include units, clearly show the shape of the curve(s) that you draw, and the value(s) at any minimum points, maximum points, and points where the curvature changes. Hint: If you do your calculations using areas instead of the formulas for one-dimensional motion, you will do the calculations faster and with more likelihood of getting the correct answers.
8) What simple feature of the graph of velocity versus time tells you the time at which the cart has the maximum displacement? Hint: Use physical reasoning in addition to math.
9) Compare the time intervals in which the cart is speeding up / slowing down with your graph of acceleration versus time. Can you determine a relationship between acceleration and velocity that reliably predicts whether the cart is speeding up or slowing down?
Important: You should have concluded that the cart is speeding up when acceleration and velocity have the same sign, and slowing down when acceleration and velocity have opposite signs. If you did not get that result, please check with your instructor or TA.
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 2004 Bedrosian