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Net Force Lab
INTRODUCTION
Newton’s second law states that the acceleration of an object is directly
proportional to the net force acting upon it and inversely proportional to the
object’s mass. In this experiment you will use vector analysis to determine the
force required to produce a system in equilibrium. You will then use your
knowledge of Newton’s second law to determine the theoretical acceleration on
an object that experiences a net force. This value will then be compared to an
experimental value for acceleration determined from the equations of motion.
SAFETY
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Review the lab safety guidelines. Always follow correct procedures in the lab.
Moving masses could prove hazardous. Be careful not to let moving masses
fall on you or pinch any fingers.
OBJECTIVES
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Predict the force necessary to counter balance the resultant force of one or
more force vectors.
Compare predicted values to experimental results through calculating percent
error.
Determine the acceleration of a mass using Newton’s second law and
comparing that acceleration to experimental results.
MATERIALS
force table and accessories
set of masses
string
meter stick
stopwatch
long wooden planks
PROCEDURE
Part 1: Prediction of the required force to achieve equilibrium.
For the following situations predict what the unknown vector’s magnitude and
direction must be in order to yield a zero net force. In order to do this you will
need to use graph paper. You may make your predictions graphically using scale
drawings or algebraically using trigonometry.
1.
2.
3.
4.
A 2 Newton force at zero degrees.
A 2 Newton force at zero degrees and a 2 Newton force at 90 degrees.
A 2 Newton force at zero degrees and a 4 Newton force at 270 degrees.
A 2 Newton force at zero degrees, a 2 Newton force at 60 degrees, and a 5
Newton force at 180 degrees.
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Part 2: Experimental determination of the force to achieve equilibrium.
Set up the above situations on the force table and determine the magnitude and
direction of an additional force that would cause the net force to be zero.
Compare your predictions to the experimentally measured force values and angles
by finding the percent error for all four situations.
Part 3: The acceleration of a system when a net force is present.
Use a longer string so that both ends hang down to the bottom of the force table
base. Hang 200 grams from one end of the force table and 200 grams from the
opposite end. Add the minimum amount of mass that will cause the mass system
to accelerate.
1. Determine the net force on the system and calculate the theoretical
acceleration of the system using Newton’s second law.
2. Calculate the experimental acceleration of the system by measuring the
distance and time the object falls assuming it starts from rest.
3. Determine the percent error between your calculated theoretical value for
acceleration and the experimental acceleration.
ANALYSIS
1. Show all work for part 1.
2. Give the mass and force values for all counter balancing resultant forces
for part two. Be sure to include the magnitude of the force as well as the
direction.
3. Calculate the % error between your predicted value and the
experimental value for both magnitude and direction of the counterbalance forces for part 1 and part 2.
4. From part three, show the calculation for the theoretical value for
acceleration of the system.
5. From part three, create a data table including the trial, displacement,
time, average velocity calculation, and acceleration.
6. Show a sample calculation for the work done in order to calculate the
average velocity and acceleration values for part three.
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