Back to 'Unit 6: Rotational Statics and Dynamics'

Topic outline

  • 6.1: Conditions for Equilibrium

    Collapse all Expand all

    When an object is in equilibrium, the forces acting upon the object are balanced. That is, the net force on the object is zero. For this to occur, the object must either not be moving, or it must be moving at a constant velocity.

    There are two types of equilibrium: static equilibrium and dynamic equilibrium.

    1. Static equilibrium describes a system that is balanced and does not rotate. An example is a seesaw where two children sitting at either end are exactly the same weight. Since the seesaw will not move, it is in static equilibrium.

    2. Dynamic equilibrium describes a system that is balanced, but also moving (without any angular acceleration). An example is a planet in perfect circular orbit around its parent star. There is no torque acting on the planet making it orbit faster or slower, but it will keep orbiting for a very long time. The system is in equilibrium, and because it is moving, it is dynamic.