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) “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.
B) When you record graphical data, you should always record ONLY the RELEVENT 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.
C) 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.
D) 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.
E) Slow and/or gentle pushes and pulls almost always gets you better data than fast and/or hard.
F) 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.)
G) You can hurt yourself with the fans. PLEASE BE VERY CAREFUL!!
Position-Time and Velocity-Time Graphs
1.
Observe the following motion of without taking any data. Place the cart on the track, ½ meter away
from the motion detector. Give the cart a quick, hard push away from the motion detector and let it
go. Catch the cart when it gets to the end of the track. Take 1 or 2 minutes to sketch an
INDIVIDUAL prediction of what the graphs of position versus time and velocity versus time will
look like for this motion. FRICTION SHOULD BE IGNORED in your predictions. Sketch one
graph with the axes labeled position and time. Sketch a second graph with the axes labeled velocity
and time. Title both of your graphs “moving away at constant velocity”.
Push and release--keep hand
out of way of motion detector
Once you have made your prediction, take another 1 or 2 minutes to compare your predictions with
others in your group. Justify to each other why your graphs correct. Make changes to your predictions
if you want to. However, prediction graphs are never graded for correctness.
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, rtp, Mechanics, L1A3-1 (Velocity
from Position).mbl Set up the equipment shown above. Practice the motion above (giving the cart a
push and stopping it at the end of the track) a few times. Keep in mind that you have to keep your
hand (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
Copyright@1999-2001 Cummings, Laws, Thornton, Sokoloff
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. Record the actual data on your activity sheets. Label your graphs as in the
prediction step. Make sure that you include only relevant data in your sketch of the graph.
3. Do your prediction graphs and actual graphs agree? If not, one of them is wrong. Determine which
one it is. If your actual data is not correct (because you got your hand in the way of the detector or
got too close to the detector or something) you must retake your data. Experimental results will be
graded for correctness. Remember to record only relevant data.
4. Now consider the following motion: The cart is started at the point farthest from the motion
detector, given a push and released as shown in the figure below. The cart is stopped half a meter
from the detector. Sketch a graph of Position vs Time and Velocity vs. Time for this motion.
Push and release--keep hand
out of way of motion detector
Compare your sketch with others in your group. Justify to each other why you believe that the
graphs that you drew are correct. Come to a conclusion as a group.
Write out the following sentence on your activity sheet:
Motion away from the motion detector (our origin) results in a _______ velocity while motion
toward the motion detector results in a _______ velocity. Fill in the blanks with “positive” or
“negative” based on the motions discussed so far. This statement establishes the coordinate system or
“sign convention” for all velocity measurements you will make in this course. Explain how this “sign
convention” for velocity is consistent with slopes of the Position vs Time graphs you made in questions
#4 and #2 above.
5.
6. For velocity vs. time graphs, describe (in complete sentences) what features are the same for a cart
moving away slowly and a cart moving away more quickly. What features are different? Repeat for
position vs. time graphs.
7. Are the two motions that we have studied so far “constant acceleration motions”? What is the value
of acceleration in these cases? Are they “constant velocity motions”?
Velocity-Time and Acceleration-Time Graphs
You open the file you will need for this part of the activity by going File, Open, rtp, Mechanics,
L2A3-1 (Slowing Down).mbl You do not want to save your old file.
8. Mount the fan on the cart so that it is secure. Without taking data, observe the following motion.
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. (See figure at the top of the next page). This motion is a constant (non-zero) acceleration
motion. Justify this statement without taking data.
Copyright@1999-2001 Cummings, Laws, Thornton, Sokoloff
Start from rest
9.
Fan Unit
Take 1 or 2 minutes to sketch an INDIVIDUAL prediction of what the graphs of Acceleration vs
Time and Velocity vs Time will look like for this motion (shown above). Ignore stopping the cart at
the end of the track. Label the axes of your graphs appropriately. Title your graphs “moving away
and speeding up”. Take another 1 or 2 minutes to compare your predictions with others in your
group. Justify to each other why you believe your graphs are correct. Come to a conclusion as a
group about what you expect the graphs to look like.
10. Set up the equipment as shown above. Practice the motion and then take and record the actual data
on your activity sheets. Ignore stopping the cart at the end of the track. Label your graphs as in the
prediction step above. Make sure that you include only relevant data in your sketch of the graph. Do
your prediction graphs and actual graphs agree? If not, one of them is wrong. Determine which one
it is. If your actual data is not correct (because you got your hand in the way of the detector or got
too close to the detector or something) you must retake your data. Experimental results will be
graded for correctness. Remember, record only relevant data.
Wondering what the position versus time graph would look like for this motion?
You can display that graph by doing the following: Point your cursor to the word
acceleration on the y axis of the bottom graph and left click. You will get a check
box option menu. Remove the check from acceleration and add a check next to
distance.
11. Predict what the velocity-time and acceleration-time graphs would look like for the following
motion:
Cart moves away from the motion detector, slowing down at a steady rate.
12. Without taking data, observe the following motion (shown below): Start the cart at the far end of the
track. Orient the fan so that, if you give the cart a push to get it moving toward the motion detector,
the cart will slow down at a steady rate (fan opposes push). Stop the cart at the point that it
begins to reverse direction or when it is 0.5 meters away from the detector, whichever comes
first. Take 1 or 2 minutes to sketch an INDIVIDUAL prediction of what the graphs of
Acceleration vs Time and Velocity vs Time will look like for this motion. Ignore the push and the
stop of the cart. Label the axes on your graph appropriately. Title your graphs “moving toward and
slowing down”. Take another 1 or 2 minutes to compare your predictions with others in your group.
Justify to each other why your graphs are correct.
Push and release
Fan Unit
Fan opposes push
13. Set up the equipment shown above. Practice the motion. When you are confident that you can do it,
take and record the actual data on your activity sheets. Label your graphs as in the prediction step
above. Make sure that you include only relevant data in your sketch of the graph. Do your
prediction graphs and actual graphs agree? Retake data if necessary.
Copyright@1999-2001 Cummings, Laws, Thornton, Sokoloff
14. Predict what the velocity-time and acceleration-time graphs would look like for the following
motion: Cart moves toward the motion detector, speeding up at a steady rate.
15. State in words how the signs (directions) of velocity and acceleration are related. Is the acceleration
positive if the object is speeding up? Is the acceleration negative if the object is down?
16. Without taking data, observe the following motion (shown below): Start the cart at the far end of the
track. Orient the fan so that, if you give the cart a push to get it moving toward the motion detector, the
cart will slow down at a steady rate (fan opposes push). Allow the cart to move closer to the detector
(slowing down as it goes), reach its closest point and then reverse directions- heading back away from the
detector (speeding up as it goes). Take 1 or 2 minutes to sketch an INDIVIDUAL prediction of what
the graphs of Acceleration vs. Time and Velocity vs. Time will look like for this motion. Ignore the
push and the stop of the cart. Label the axes on your graphs appropriately. Title your graphs “moving
toward and away”. Take another 1 or 2 minutes to compare your predictions with others in your group.
Justify to each other why your graphs are correct.
Push and release
Fan Unit
Fan opposes push
17. Set up the equipment shown above. Practice the motion. The turn around point for the cart
MUST BE AT LEAST ½ METER FROM THE MOTION DETECTOR.!!! When you are confident
that you can do this, take and record the actual data on your activity sheets. Label your graphs as in the
prediction step above. Make sure that you include only relevant data in your sketch of the graph. Do
your prediction graphs and actual graphs agree? If not, one of them is wrong. Determine which one it is.
Retake data if necessary. Experimental results will be graded for correctness. Remember, record only
relevant data.
18. At the point that the cart reverses its direction of motion (the turn around point), is the velocity
positive, negative or zero? Is the acceleration at this point positive, negative or zero?
Copyright@1999-2001 Cummings, Laws, Thornton, Sokoloff