Equilibrium

For an object to remain in equilibrium, two conditions must be satisfied - both the net force and the net torque must be equal to zero.

ΣF = 0

Στ = 0

An example of an object in equilibrium is a rod that is free to rotate about a hinge at one end. It is held horizontally, with the torque due to the force of gravity being balanced by the torque from a force with a vertical component applied at some point along the rod.

What, if anything, happens when the upward force F is moved a little to the right, away from the hinge? To maintain equilibrium:

  1. The magnitude of the upward force F increases. (4/32) (12%)
  2. The magnitude of the upward force F decreases. (2/32) (6%)
  3. The magnitude of the downward hinge force increases. (0/32) (0%)
  4. The magnitude of the downward hinge force decreases. (0/32) (0%)
  5. Both 1 and 3 (1/32) (3%)
  6. Both 1 and 4 (3/32) (9%)
  7. Both 2 and 3 (1/32) (3%)
  8. Both 2 and 4 (21/32) (66%)
  9. None of the above. (0/32) (0%)















Note also what happens as the direction of the force is varied, but with the force being applied at a fixed position on the rod.