AP Physics Lab: Newton's 2nd Law of Motion #2
(“Precipice” Problem)
Background
If an object has a net force exerted on it, it will accelerate. Force and acceleration both have direction as well as
size. The acceleration is in the same direction as the force causing it. If the force is in the positive direction, so
will be the acceleration. Similarly, if the force is in the negative direction, so will be the acceleration.
According to Newton's second law ( F = m a ) the net force on an object causes it to accelerate.
For this activity, you will apply a constant force to a Dynamics Cart and compare the cart’s actual acceleration
against your prediction of its acceleration.
Objectives

to investigate the acceleration due to an applied force
Materials
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dynamics cart and track
balance
hanging masses
interface and probe set (smart pulley)
Part I: Setup
1. Place the Dynamics Track on a horizontal surface.
Level the track by placing the cart on the track. If
the cart rolls one way or the other, use the
adjustable feet at one end of the track to raise or
lower that end until the track is level and the cart
does not roll one way or the other.
2. Attach the Smart Pulley to one end of the track as
shown in the diagram at right. Connect the cart
to a hanging mass by passing a cord over the
smart pulley.
3. Connect the smart pulley to the computer via a SW500 interface.
4. Set the Start Option to automatically start when a spoke first clears the laser. Set the Stop Option to
automatically stop before the cart has reached the end of the track.
5. Create a triple graph of d vs t, v vs t, and a vs t from which to determine the acceleration of the cart.
Part II: Data Recording
Note: Before recording data for analysis, record a trial run.
1. Record a data run by allowing the cart to be pulled by the hanging mass.
*** Be certain to protect the Smart Pulley and cart from damage. ***
2. Record a run for each member of the Team (and a spare).
AP_L_2x02_Newtons2ndLaw2
Note:
Work (show all work) and answers (clearly mark all answers) for all of the following may be hand written
but MUST be clearly legible and organized.
Part III: Preparing Your Prediction
1.
2.
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4.
5.
Record the mass of the cart (mC), riders (mR), cord (mS), and hanging mass (mH).
How much mass is being moved?
How much mass is causing the motion?
What force (name and amount) is causing the motion?
What should the acceleration of the cart system be?
Analyzing the Data
1.
2.
3.
4.
5.
From the d vs t graph, determine the system’s acceleration. Annotate the graph accordingly.
From the v vs t graph, determine the system’s acceleration. Annotate the graph accordingly.
From the a vs t graph, determine the system’s acceleration. Annotate the graph accordingly.
Determine the average of your experimental accelerations.
Using your prediction as the accepted value, what is the relative percentage of error for your
experiment?
6. Was the actual acceleration greater than or less than your prediction? Cite at least two possible causes
and (directionally) support your causes.
7. Attach all support materials.
Lab_1x06_Newtons2ndLaw2