Martin Ray A. Arcibal
5̊ AP Fiziks
Mr. Tillay
25/09/12
Newton’s Second law – Constant Mass, Changing Force (Motion Sensor)
1. Purpose
The purpose of this experiment is to test the validity of Newton’s second law of motion,
which states that the acceleration of an object is directly proportional to the net force applied to
the object and inversely proportional to its mass. This experiment will test only the first half of
the law (regarding the change in the net force), since the mass of the whole system will remain
unchanged throughout the lab.
2. Hypothesis
Increasing the magnitude of the net force exerted on an object, while keeping the mass
constant, will cause it to accelerate. In maintaining constant velocity, a force that equals the
magnitude of the resistance imposed by friction is exerted on the object, which means that the
net force on the system is zero. Increasing the force exerted on the object will cause it to
overcome friction and accelerate.
3. Experimental Design
Control Variable: the mass of the entire system
Independent Variable: the net force exerted on the cart
Dependent Variable: the acceleration of the cart
4. Procedures
a. Open the DataStudio file: 15A Newton’s 2nd Law 1.ds.
b. Acquire the mass of the cart, the hanger, and the whole cart and hanger system.
c. Set-up the pulley system, with the first run having two 20-g weights on the cart and one
20-g weight on the hanger. Start the program once the cart is released
d. For the second run, transfer one 20-g weight from the cart to the hanger. Start the
program once the cart is released.
e. For the third run, transfer the last 20-g weight from the cart to the hanger. Start the
program once the cart is released.
f. For each run, highlight a smooth part of the graph, choose fit, then choose linear fit.
g. Acquire the slope of each run.
5. Prediction Questions (Lab 15A Hand-Out)
a. What happens to an object when you apply a net force to it?
Applying net force on an object will cause it to accelerate.
b. What happens to the motion of an object if it has a constant mass but you change
the magnitude of the net force on it?
The acceleration of the object will be directly proportional to the change in the magnitude
of net force applied to it.
6. Sketch of the Resulting Graph (Lab 15A Hand-Out)
y
x
7. Data
Data Table 1:
Item
Run #1: Total mass of the hanger and 20-g mass (mH):
Run #1: Total mass of the cart and two 20-g masses (mC):
Run #2: Total mass of the hanger plus masses:
Run #3: Total mass of the hanger plus masses:
Data Table 2:
Run
Acceleration (m/s2)
#1
0.390
#2
0.685
#3
1.05
Data Table 4:
Run
#1
#2
#3
Data Table 3:
Run
Mass, hanger (kg)
#1
0.0252
#2
0.0452
#3
0.0652
Acc., theory (m/s2)
0.437
0.784
1.13
Acc., exp. (m/s2)
0.390
0.685
1.05
Mass (kg)
0.0252
0.540
0.0452
0.0652
Fnet(N)
0.247
0.443
0.639
% difference
10.8%
12.6%
7.08%
8. Questions (Lab 15A Hand-Out)
a. Why did the slope change for each run?
The rate of change of the velocity of the object changed each turn. The slope increased
for each run, signifying an increase in acceleration, since in a velocity versus time graph,
the slope of the graph is also known as the acceleration of the object.
b. For runs #1, #2, #3, what did you observe about the slope of the Linear Fit as the net
force increased but the total mass was kept constant?
The slopes of the graph increased from run #1 to run #3, showing steeper slopes with
each succeeding run. This is the result of the increased net force applied on the cart.
c. What are the units for the slope of each graph? Explain.
The unit for the slope of each graph is meters per second per second (m/s/s) or meters per
second squared (m/s2). This is the result of acquiring the change in velocity of an object
(y values) over a certain period of time (x values). Since the slope can be acquired from
dividing Δy (m/s) by Δx (s), the corresponding units, after all of the calculations, should
be m/s/s, or m/s2.
d. What happens to an object’s acceleration if the net force applied to the object is
increased but the object’s mass remains constant?
Increasing the net force applied to the object and preserving its mass would increase the
object’s acceleration.
9. Error Analysis
During the course of the experimentation, the investigators encountered a problem with the
consistency of the graphs. At some point near the end of the track, the cart experienced varying
rates of acceleration. This can be attributed to friction existing on that point. The investigators
may have failed to clear out the dust and grime present on the track, which made the presence of
friction more apparent at that point than the rest of the track. Another possibility is the faulty in
the pulley system set up by the investigators. This may have interfered with the movement of the
string through it, creating fluctuations in the acceleration of the object. Also, the motion sensor
may have caught the movement of the investigators, resulting in the varying rates of acceleration
found in the graph. All in all, a combination of systematic errors and the mistakes of the
investigators caused unwanted fluctuations to occur.
10. Conclusion
According to the data in tables 1 through 4 and the graphs provided, acceleration increased
when the net force applied to the object increased and the mass remained constant. This proves
that the acceleration of an object is directly proportional to the net force applied. Increasing the
net force applied on the object will cause it to accelerate. This validates the first part of Newton’s
second law of motion. The second part of this investigation should be to prove the truthfulness in
the second part of the said law of motion.
Run 1
Run 2
Run 3