Studio Physics I
Newton's Laws in One Dimension
Remember:
1. .mbl files only transfer from the webpage with Internet Explorer. Netscape does not work.
2. To collect data, click the collect button on the data collection software, count to two (to let the
data collection begin) or 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.
1. Open the LoggerPro file pos,vel,acc.mbl and
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). Click the
collect button on the data collection software, count to two (to let the data collection begin) and then let
the cart go. The cart moves away from the motion detector speeding up at a steady rate (constant
acceleration). Sketch the graphs of the carts velocity and acceleration. Sketch prediction graphs the
applied and net force on the cart after it is released and during the time the cart is moving under the
influence of the constant force. Applied and net force are the same in this case. Why? "Sketch" means
that you should carefully show the shape of the curve produced, but don't bother with exact numbers on
the graph.
2. 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. Collect data as the cart
moves away from the motion detector speeding up at a steady rate (constant acceleration). On your
sketches from above, draw the velocity and acceleration of the cart for this case 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? 
3. Remove the friction pad from the cart. The frictional force acting on the cart is again very small and
can be ignored.
COPYRIGHT1999, 2000 K. Cummings
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). Sketch the velocity, acceleration and prediction of net force for this motion after the cart is
released and before it is stopped.
4. 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) Sketch the velocity and acceleration of
the cart and your prediction of the force on the cart after the cart is released.
5. In question 4 above: Why is the net force on the cart essentially the same as the applied force? How
does the acceleration at the point the cart reverses direction compare to the acceleration just before it
reverses direction? Predict how the force at the point the cart reverses direction compares to the force just
before it reverses direction?
We will now use the computer to simultaneously measure a force and acceleration in order gain
confidence in our predictions of the force graphs discussed above. The measurements are to be made on
an oscillating system consisting of a weight and a spring.
Get the file "forceonly.mbl" from your harddrive, cd or the course web page. Open the file by double
clicking on the file. The first thing that you need to do is set the force probe measurement to zero
when there is nothing on the probe. To do this, remove everything from the force probe and click
the “ZERO” button on the tool bar. You can now use this software to QUALITATIVELY measure
the force exerted on the force probe by the oscillating spring-mass system. We stress qualitatively here,
because the force probe has not yet been calibrated, so the numbers may not be correct. However, the
shape of the curve will be.
6. Set the spring-mass system in motion by pulling the mass slightly downward from its resting position.
Collect data. Sketch the force versus time graph. "Sketch" means that you should carefully show the
shape of the curve produced, but don't bother with exact numbers on the graph.
7. Based on your understanding of the relationship between force and acceleration, sketch a prediction of
what you think the acceleration versus time graph should look like.
8. Get the file "force and acceleration.mbl" from your hard drive, cd or the course web page. Open the
file by double clicking on it. The first thing that you need to do is set the force probe measurement
to zero when there is nothing on the probe. To do this, remove everything from the force probe
COPYRIGHT1999, 2000 K. Cummings
and click the “ZERO” button on the tool bar. Use the force probe and motion sensor to measure the
acceleration and force of the oscillating system simultaneously. Is the actual graph of the acceleration of
the mass-spring system what you predicted? If not, your prediction may be in error, or your measurement
may be in error. Determine which one it is. Sketch the actual graph of acceleration versus time for the
oscillating system.
9. Describe in words why the graph of force and the graph of acceleration compare the way that they do.
That is, describe how the relationship between force and acceleration is represented in the comparison of
these two graphs. If necessary, correct any of your predicted force graphs from above.
10. List all of the forces acting on the weight.
11. Consider the motion of the mass after it passes through its equilibrium or zero point, while it is on
the way down to its lowest point. What is the direction of velocity of the mass? What is the direction of
acceleration for the mass? Is the mass slowing down or speeding up in this region of its motion?
Describe how your answers to the first two questions above are consistent with your answer to the third
question.
12. Consider the motion of the mass after it passes through its lowest point, while it is on the way back
up, but before it passes through its equilibrium or zero point. What is the direction of velocity for the
mass? What is the direction of acceleration for the mass? Is the mass slowing down or speeding up in
this region of its motion? Describe how your answers to the first two questions above are consistent
with your answer to the third question.
13. Is there a force exerted on the mass when the mass is at its lowest point? If so, what is the direction
of that force? Is there a force exerted on the mass when it is at its highest point? If so, what is the
direction of the net force exerted on it then? What are the directions of the acceleration of the mass at
these two points?
COPYRIGHT1999, 2000 K. Cummings