What You Do:
- Ask the adult helper to stack one fist on top of the other and extend their arms until his elbows are straight. Feel free to have them growl, or make noises indicating how strong they are!
- Have your child place two fingers on the top fist, and two on the bottom fist. When she's ready, have her quickly push the fists in the opposing directions.
- She'll notice how easy it was to separate the strong fists, and may not believe she could possibly be that strong. Have her try it one more time so as to confirm her power.
- This time, have the adult volunteer, push his fists together even more fervently than before and have your child repeat the experiment.
- This was even easier! Why?
Explain to her that when the fists are stacked, pushing together, it creates a vertical force. Vertical forces can only push up and down, not side to side. So, when she pushed side to side with her super strength, (or horizontal force), she disabled the balance of the vertical force, making it impossible for the adult to keep his fists stacked.