Newton's Laws in Action

On Saturday, we were at my sister's gymnastics class and I noticed a beginner's class jumping over small, padded blocks. As the kids jumped one by one, I realized that this was Newton's laws in action.
In order for the kid to jump over the block, he had to be able to exert enough upward force to counter the downward pull of gravity. By doing this he would be changing his net force. Initially, before he jumped, the boy would have a net force of zero and he was at equilibrium. At this point, the free body diagram would have two equal forces, the downward force of weight and the upward normal force.
However, in the instant that he jumped, by pushing off from the ground, the boy had increased the upward force and therefore caused his body to rise off the ground. In this instant his net force is no longer zero because the greater upward force means the two forces no longer cancel out.