Static Equilibrium

     Static Equilibrium is when an object has many different size forces acting upon it, but the sum of forces equals zero.

For example, have you ever tried balancing a pen on your finger? It won't balance in the middle because the forces are unequal. You have to find the balance point, or the fulcrum (which in this case is toward the cap of the pen). At this very point there is static equilibrium- the forces acting on the pen are unequal but are zero at this very point.

Here is another example:

These birds balance on your fingertip. Normally, they would fall off because the forces are not balanced. The birds are weighted just right, however, that the fulcrum is on the beak. Here there is static equilibrium.

Bridges also use the concept of static equilibrium. Bridges need to be durable and be able to withstand lots of weight. Different bridge types use different methods to ease the force on the horizontal bridge itself. This is an example of how suspension bridges work.