@emma >i just cant see how a contact lens can fall out
The force keeping them in place is pretty small, thus extremely vigorous activity can cause them to fall out, same as anything that causes your eyes to become excessively moist.

>my glasses fall all the time though
Glasses that aren't properly adjusted with a loose fit will fall of all the time.

You should be able to throw your body and head forwards and then suddenly stop without your glasses moving.

High forces like jumping from 2m causes them to move forward a bit, but you just throw your head back to reset them.