Balancing Tournament Lab

Materials: School Network and Macintosh Computer w/Interactive Physics

Time Allotment: 3 Class Days


The purpose of this activity is to apply the principle of equilibrium and balanced torques to the solutions of balance problems.

Getting Ready:

This lab must be done on a Macintosh computer connected to the school network or upon a computer in the Science Computer Lab. To prepare for the lab, do the following steps.

Situation A:

An evil physics teacher has developed a game to test if her students really understand how to calculate torque. In the game, a balance beam is suspended over a mud pit. One student hangs from each side of the beam. Bob and Carmen have been chosen as the first of the unfortunate students to play. Their goal is to place themselves along the beam so it remains balanced. If Bob and Carmen are wrong, both of them will be dropped into the mud!

Make a Prediction:

The weights shown in the boxes below represent the students' weights. Bob weighs 400 N. By carrying extra weights, Carmen can weigh any amount. For each question, calculate what Carmen's weight must be to bring the beam into balance. Record your prediction in the space provided. Remember, torque = force x distance.

The beam itself weighs 800 N and its weight is evenly distrubuted along its length. There are nine positions along the beam from which Bob and Carmen may hang. The spacing between the position is 1.00 m.


  1. Carmen's weight (required to balance the beam) must be ______________ N.

  2. Carmen's weight (required to balance the beam) must be ______________ N .

  3. Carmen's weight (required to balance the beam) must be ______________ N.

  4. Carmen's weight (required to balance the beam) must be ______________ N.

  5. Carmen's weight (required to balance the beam) must be ______________ N.

  6. Carmen's weight (required to balance the beam) must be ______________ N.

  7. Carmen's weight (required to balance the beam) must be ______________ N.



Run Simulation: Set Number of students, Carmen's weight, Carmen's position, Bob's position, and Fulcrum position as required in Question 1. Click the Run button and observe the simulation. If your prediction is incorrect, make a new prediction and repeat the simulation until you succeed in balancing the beam. Record Carmen's weight from the simulation in Table 1. Remember to click the Reset button before changing any values. Repeat the above steps for Questions 2-7.


Table I: Simulation Results for Carmen's Weight

Question 1


Question 2


Question 3


Question 4


Question 5


Question 6


Question 7





Explain in detail how the principle of balanced torques can be utilized to determine if an object will balance. In your explanation, use a specific quantitative example to illustrate the principle.











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This page created by Tom Henderson and last updated on 1/26/98.

Special thanks to lab assitant Dan Reid for assistance with the typing.