Studio Physics I
Newton's Laws in One Dimension
Remember:
1. Use “LoggerPro” software to collect and analyze data
2. To collect data, click the collect button on the data collection software, listen for the ticking of
the motion detect and then let the cart go.
3. Keep your hands and everything else clear of the motion detector. It will detect whatever is
closest and that may not be the cart if you are not careful.
4. The motion detector cannot pick up anything closer that ½ meter away.
5. Make sure the track is level.
6. "Sketch" means that you should carefully show the shape of the curve produced, but don't bother
with exact numbers on the graph.
You open the file you will need for this activity by going File, Open, <Your Physics1 Data
Folder>, L03A2-1 (Motion & Force).mbl .
1. Set up the equipment shown below.
Release from rest--keep hand
out of way of motion detector
The frictional force acting on the cart is very small (almost no friction) and can be ignored. The cart
is pulled with a constant force (the applied force, due to the weight hang on the string). Take 2 or
3 minutes to sketch an INDIVIDUAL prediction of what the following four graphs will look like for
the motion shown above (cart starts close to the motion detector and moves away speeding up at a
constant rate). Sketch predictions of a) acceleration versus time b)velocity versus time c) applied
force (from the string) versus time and d) net force vs time. Ignore the stop at the end of the track.
Label your graphs “moving away and speeding up”. Applied and net force are the same in this
case. Why? Take another 2 or 3 minutes to compare your predictions with others in your group.
Justify to each other why you believe that the graphs that you drew in the step above are the correct
graphs. Come to a conclusion as a group about what you expect the graphs to look like.
2.
With the equipment set up as shown above, practice the motion. Then take and record the actual data
on your activity sheets. Ignore the stop 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.
COPYRIGHT1999, 2000, 2001 Thornton, Sokoloff, Laws, Cummings; Rev. 2003 Bedrosian
3. Take the friction pad provided and mount it on the bottom of the cart. The frictional force acting on
the cart is now increased. Set the cart up again as shown in the figure above. The cart is pulled with
the same constant force (the applied force due to the weight) as in question above. Adjust the
friction pad so that the cart still moves under the pull of the hanging weight, but also make sure that
the pad is dragging on the track to introduce a frictional force. (Fold the felt to make three layers and
staple them if needed.) The cart starts close to the motion detector and moves away speeding up at a
constant rate. Take 2 or 3 minutes to sketch on your graphs from above, an individual prediction
of the velocity and acceleration of the cart and predictions of applied and net force on the cart after it
is released. Note that the applied and net force are different now. Why? Which determines the
acceleration?
4. Practice the motion (cart starts close to the motion detector and moves away, speeding up as it goes).
Then take and record the actual data on your activity sheets. Ignore the stop 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.
5. Remove the friction pad from the cart so that you can ignore friction again.
Push on cart (not on force
probe) and release--keep
hand out of way of motion
detector
6. As shown in the above picture, start the cart as far away from the motion detector as possible and
give it a gentle push toward the motion detector and then let go. A constant force pulls it in the
direction away from the motion detector. The cart moves toward the motion detector slowing
down at a steady rate (constant acceleration), comes to rest momentarily and then moves away
from the motion detector speeding up at a steady rate. Before taking any data, sketch your
individual prediction of the velocity, acceleration and net force for this motion after the cart is
released and before it is stopped. Label your predictions “motion toward the detector, slowing down
at a constant rate”. Compare your predictions with those in your group.
7. Practice the motion above. DO NOT let the cart get closer than ½ meter from the detector. Then
take and record the actual data on your activity sheets. Ignore the push to start the cart and the stop 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.
8. State in words how the signs of velocity and acceleration are related for speeding up and slowing
down. Is the acceleration always positive if the object is speeding up? Is the acceleration always
negative if the object is slowing down? State in words how the sign of acceleration is related to the
sign of force. If the acceleration of an object is constant, does the net force acting on the object have
to be constant too? Is there ever a situation where the net force and acceleration are not in the same
direction?
COPYRIGHT1999, 2000, 2001 Thornton, Sokoloff, Laws, Cummings; Rev. 2003 Bedrosian