Download AP Physics Lab 2x01: Newton`s Second Law of Motion

AP Physics Lab 2x01: Newton's Second Law of Motion
Background
Newton's first law states that if there is no net force on an object, there is no acceleration. In other
words, the object moves at constant velocity. But how much will an object accelerate when there is a
net force? Think about pushing a bowling ball. The harder you push, the faster the velocity of the ball
will change. The larger the force, the larger the acceleration, the rate of change in velocity. Acceleration
is found to be directly proportional to force.
Acceleration also depends on the mass of an object. Masses of bowling balls vary; some are small,
others large. If you exert the same force on a less massive ball, its acceleration will be larger. In fact, if
the mass is half as much, the acceleration will be twice as large. The acceleration is inversely
proportional to the mass. These relationships are true in general and are stated in Newton's second
law: the acceleration of a body is directly proportional to the net force on it and inversely proportional
to its mass. Newton's second law may be summarized as
F=ma
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, a net force on an object causes it to accelerate. In
addition, the larger the mass of the object, the smaller the acceleration. (Note that the larger mass does,
however, have a larger inertia.)
For this activity, you will apply a varying force (push and pull) to a Dynamics Cart on a level Dynamics
Track. Using theMotion Sensor tomeasure themotion of the cart, the Force Sensor tomeasure the force
you exert on the cart, you can use DataStudio to show the relationship of force to acceleration of a
moving mass.
Objectives
 to demonstrate the relationships expressed in Newton’s 2nd Law
Materials
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dynamics cart and track
balance
interface and probe set (force probe, motion sensor)
AP_L_2x01_Newton’s 2nd Law
Part I: Setup
1. Connect the SW500 interface to the computer, turn on the interface, and turn on the
computer.
2. Connect the Motion Sensor’s phone plugs to Digital Channels 1 and 2 on the interface.
3. Connect the DIN plug of the Force Sensor to Analog Channel A.
4. Data recording should be set at 20 Hz for the Force Sensor and 20 Hz for the Motion Sensor.
5. Create a Force vs Acceleration graph to display collected data.
6. Set the Start Option to None.
7. Set the Stop Option to 15 s.
8. 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.
9. Mount the Motion Sensor at the end of the track.
10. Place the cart on the track and attach the force sensor so the hook end of the sensor points
away from the Motion Sensor. Since the cart must remain a minimum distance of 15 cm away
from the Motion Sensor, put a temporary mark on the track at this minimum distance.
Part II: Trial Run of Data
Note: Before recording data for analysis, record a trial run.
1. Place the cart on one end of the Dynamics Track.
2. Press the tare button on the side of the Force Sensor to zero the Force Sensor.
3. Firmly grasp the hook of the Force Sensor and pull and push the Force Sensor to make the cart
move back and forth. Make sure the cart does not come too close to the Motion Sensor.
Record a sample set of data.
Part III: Data Recording
1. Prior to recording each data run, remember to press the tare button on the side of the Force
Sensor to zero the Force Sensor.
2. Record a data run for each lab team member.
Analyzing the Data Submit a “Responses Page” (with an appropriate heading) for these questions.
1. Highlight the region of your force vs acceleration graph that shows the movement of the cart.
Turn off the connecting lines. Determine the slope of the Best Fit Line. Print and attach this
graph to your Response Page.
2. What are the appropriate units for the slope of your Force vs Acceleration graph? Support your
answer.
3. Based on your graph, what is the combined mass of the cart & force sensor? Support your
answer.
4. Based on your Lab Team’s runs (include a table of Run#, TeamMemberName, and
CalculatedMass for all runs), what is the (average) combined mass of the cart & force sensor?
5. What is the actual combined mass of the cart & force sensor?
6. What is the relative percentage of error between answers 3 and 5?
7. What is the relative percentage of error between answers 4 and 5?
8. What are some possible reasons for the difference between answers 3 and 5?
9. Which calculation is more accurate, #3 or #4? What (specifically) contributed to the accuracy?
AP_L_2x01_Newton’s 2nd Law