Names:
Static Equilibrium Lab
Purpose
 To calculate the force required for the system to be in static equilibrium
 To create a system in static equilibrium
Procedure
Part 1:
1. Using a mass and string, construct a pendulum from a ring stand
2. Pull the pendulum away from the vertical by some angle θ1, measure (T)ension in string.
3. Repeat for a different angle θ2 (θ can be measured using a protractor or calculated by
trig)
Part 2:
1. Tape a piece of polar coordinate paper to the center of the ring of the ring stand. Trim
off any excess paper hanging over the edge of the ring.
2. Get 3 masses and tie each mass with a piece of string to a single paper clip.
3. Place the paper clip in the center of the polar graph paper and arrange the masses and
strings so that the paper clip does not move from the center
4. Record the direction and magnitude of the 3 forces
5. Repeat with 3 different masses.
Calculations
Part 1:
1. Calculate the force required in string #1 in order for the system to be in equilibrium for
θ1. (Include a FBD of the system in your answer)
2. Repeat for θ2.
Part 2:
1. Calculate the magnitude of the 3 forces
2. Resolve the forces into their X and Y components
3. Sketch a FBD of the system
4. Repeat 1-3 for the second set of masses
Questions
Part 1:
m1
1. How does the increase in θ affect the force required in string #2?
2. Why?
Part 2:
1. Are your systems in static equilibrium?
2. What possible reasons and/or sources of error would result in a Fnet ≠ 0?
m2
θ String 1
m
String 2
T
Spring Scale
Pull Horizontal
m3
Names:
Worksheet Questions:
1. Five physics students wish to pull down a tree. They attach five ropes to the
bottom of the tree so each student can pull. Student #1 pulls north with a 500N
force. Student #2 pulls 55°NofE with a 600N force. Student #3 pulls 35°SofE
with a 700N force. Student #4 pulls 45°WofS with a 800N force. Student #5
“supervises.” Assuming that the tree is very rotten at the bottom and does not
resist their pulling:
a. Draw a FBD of the forces on the tree (top view, ignore FG)
b. Calculate the resultant force magnitude. What happens to the tree?
c. Calculate what force student #5 could exert to put the tree in static
equilibrium
d. What kind of grades do you think these five students should receive in
physics?
2. A 20kg picture must be hung with picture hanging cord.
a. If θ = 90°, what is the tension in the cord?
b. If θ = 120°, what is the tension in the cord?
c. This cord can withstand tension of up to 500N. What is the maximum
value of θ?
d. How do you get the maximum picture hanging ability out of a cord?
(general question, no solving necessary)
θ
20kg