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. "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 the first part of this activity by going File, Open, rtp, Mechanics,
L3A2-1 DFS (motion & force).mbl Careful, there are two files with the same number and very
similar names. Get the right one!!!
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 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
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. 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 always, 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. The frictional force acting on the cart is again very small
and can be ignored.
Push on cart (not on force
probe) and release--keep
hand out of way of motion
detector
As shown in this 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). Stop the cart at the point closest to the motion detector (before it starts
to move away). 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.
Compare your predictions with those in your group.
6. Practice the motion (cart starts far from the motion detector and moves toward it , slowing down
as it goes. Stop it at it nearest point. 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 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.
7. The frictional force acting on the cart remains very small. As in the picture above, the cart is
given a push toward the motion detector and released. A constant force pulls it in the direction
away from the motion detector. It 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. (Don’t stop it at its closest point this time)
COPYRIGHT1999, 2000, 2001 Thornton, Sokoloff, Laws, Cummings
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.
8. Practice the motion (cart starts far from the motion detector and moves toward it , slowing down
as it goes. It momentarily comes to a stop and then reverses direction, speeding up as it goes-DO
NOT stop the cart at its nearest point. 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.
9. In the question above: Why is the net force on the cart essentially the same as the applied force?
Which one does the force sensor measure? How does the acceleration at the point the cart
reverses direction compare to the acceleration just before it reverses direction? How does the
force at the point the cart reverses direction compares to the force just before it reverses
direction?
10. Predict what the velocity-time and acceleration-time graphs and net force versus time graph
would look like for the following two motions:
a. Cart moves away from the motion detector, slowing down at a steady rate.
b. Cart moves toward the motion detector, speeding up at a steady rate.
11. State in words how the signs of velocity and acceleration are related. 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?
COPYRIGHT1999, 2000, 2001 Thornton, Sokoloff, Laws, Cummings