Equilibrium Lab
Name:
Period:
Physics
In this lab we will demonstrate that when two or more force vectors are in equilibrium, the total force or net
force, as found by their vector sum, is equal to zero.
Setting Up Your Force Board
1. Lay the force board on the table so that the side with the angle markings is facing upward.
2. Hold each scale parallel to the table and examine it to make sure that it reads zero when there is no force
applied to it. If it does not read zero, adjust it by twisting the plastic nut by the handle until it is zeroed.
Part A - 2 Vectors
1. Hook two of the scales through the loops
on the force board and pull them apart.
2. Allow the strings and the force board to
adjust to the new situation, then rotate the
force board so that one of the strings is
aligned along the zero degree direction.
3. Record the force on each scale and the angle at which they pull.
First Scale
Magnitude of the Force:
Second Scale
Magnitude of the Force:
Angle:
Angle:
4. Two forces are in equilibrium if they have equal magnitudes but are opposite in direction.
a) Are these two forces in equilibrium? Explain.
b) Why would you expect the two forces to be in equilibrium? (What is the force board doing? What does the
net force have to be?)
Part B - 3 Vectors
Data Collection
1. Hook a scale to each of the three strings on the force
board and pull them outward at different angles. Number the
scales 1, 2 and 3
2. . Rotate the force board so that scale #1 is pulling to 0°.
3. Read off the magnitudes of the three forces and their
directions and enter the information into the data table.
4. Rearrange your scales so that they pull with different
force in different directions and take another set of data.
Three Vectors in Equilibrium – Trial One
#1
Scale
#2
#3
#2
#3
Magnitude of Force
Direction of Force
Three Vectors in Equilibrium – Trial Two
#1
Scale
Magnitude of Force
Direction of Force
Graphical Approach
5. For each trial:
On the graph paper below, make a scale drawing of all of the forces that you measured.
a) Use a scale of 1 cm = 1N.
b) Use the ruler and the protractor to be sure that all lengths and angles are correct.
c) Draw the vectors one by one. Draw them head to tail – so that the tail of the next vector starts from
the head of the previous vector.
d) Find the net force acting on the force board by drawing from the tail of the first force vector to the
head of the last force vector. Measure the magnitude by the length of the vector and measure the
angle with a protractor
6. What is the net force acting on the force board in each trial according to the graphical approach?
Mathematical Approach
9. For each trial:
Use trigonometry to add all of the forces acting on the force board and find the net force.
a) Break each of the forces into its horizontal and vertical components.
b) Add the components to find the total force in the vertical direction and the total force in the
horizontal direction.
c) Add the total horizontal force and the total vertical force (as vectors) to find the net force acting on
the force board.
10. What is the net force on the force board in each trial according to the mathematical approach? Does your
result make sense? Why or why not?