With this simulation, you can investigate the basic principles of equilibrium. For the beam to remain at equilibrium, the net force on the beam must be zero and the net torque on the beam should also be zero. The 100-cm long beam is assumed to be uniform, so its center-of-gravity is at the center of the beam.

Here are some things to try to see if you fully understand the concepts. If possible, predict what you think will happen and then make the changes to see if you are correct.

1. | The support forces are determined using the conditions for equilibrium, which are that the sum of all the forces must be zero and the sum of all the torques must be zero. For a particular set of weights and positions, use the equilibrium conditions to set up equations you can use to solve for the support forces. When you solve the equations, do you agree with the values calculated by the simulation?
2. | If you move the support on the right toward the right end of the board, does the force provided by the support change? If so, how? Is the sum of all the forces still zero? Is the sum of all the torques still zero?
3. | By adjusting the positions (and possibly weights) of the objects you should be able to make the force from one support equal zero. The other support would then support all the weight. In this situation, one of the two supports would have to be placed at the center-of-gravity of the system. Which support is it, the one supporting no weight or the one supporting all the weight?
4. | If you think of the beam as simply resting on the two supports, the beam would stay in equilibrium as long as each support was applying an upward force. Can you set up a situation where the beam tips over? Where is the center-of-gravity of the system in this situation? Does this explain why the system is unstable?