Balanced Torques 1
Name ______________________________________________ Date _________ Period ______
Balancing Torques
Purpose
After reading the lab, create your own purpose below:
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Pre-Lab Discussion
Suppose you are an animal trainer at a circus. For a stunt, you want to balance a 600 kg baby
elephant on a seesaw using only your own body weight. How far from the fulcrum must stand on
the other side in order for you to balance the elephant? In order to solve this problem, we need to
find a state of rotational equilibrium.
A net torque causes an object to start turning or rotating. If there is no net torque, the system
is at rest, or equilibrium. The forces in equilibrium may not be balanced, but they are applied in
such a way that there is no rotation brought on by the applied forces.
While no elephant or seesaw will be used, you will practice finding rotational equilibrium
and use it to model the elephant situation.
Materials
Masses
Mass Hangers
Fulcrum
Meter Stick
Procedure
1. Carefully balance a meterstick horizontally on the fulcrum. Adjust the center hanger until
the meterstick stays level and at rest with no weight on it. Record the point on the
meterstick that this hanger is attached to below.
2. Use Table 1 to help you suspend the first mass from the hanger at the distance given.
3. Suspend the other mass on the opposite side of the fulcrum at the point that perfectly
balances the meterstick. Adjust the weight until the stick is perfectly flat and still as
before. Record the distance of the second mass from the fulcrum in Table 1.
4. Repeat steps 2-3 for the remaining masses in Table 1.
Data
Fulcrum point on meter stick (cm): _______________
Balanced Torques 2
Table 1 – Torque Data
First Mass
Second Mass
Trial
Mass (g)
Distance from
Fulcrum (cm)
Mass (g)
1
200
20
200
2
100
20
200
3
500
5
200
4
500
10
200
5
200
15
150
6
250
25
300
7
400
40
500
Distance from
Fulcrum (cm)
Calculated
Distance (cm)
Calculations (Show 1 sample calculation below.)
1. Calculate the distance the 2nd mass should have been placed based on the information
given to you in Table 1. Record your answer as Calculated Distance in Table 1.
Questions
1. If you are playing seesaw with your younger sister (who weighs much less than you),
what two things can you do to balance the seesaw?
2. The broom is balanced at its center of gravity. If you saw the broom into two
parts through the center of gravity and then weigh each part
on a scale, which part will weigh more? Explain.
3. You want to balance the mass of a 600 kg baby elephant standing 0.743
m from the fulcrum of a seesaw. You weigh 55 kg. How far from the
fulcrum must you stand to balance the elephant? Show your work below.
Conclusion
Were there any differences between your measured distance and the calculated distance? What
could cause error in those measurements?