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by Rain Newcomb and Bobby Mercer
Topics: Fifth Grade, Science
Share Photos to Win

Have your kid easily defeat an adult in a contest of strength. Sound crazy? This trick uses vertical and horizontal forces to help your child to push apart your hands apart, no matter how hard you try to keep them together! Your child will feel like a superhero and you'll be introducing her to the science of physical forces.

 

What you need:
  • Adult Helper
  • Your Child's Amazing Strength
What you do:

  1. The adult helper (you) should make two fists and stack one on top of the other. Then, extend your arms until your elbows are straight (or as straight as possible). Your goal is to keep your fists together. Your child is going to knock your fists apart using just her fingertips.

  2. Have your child keep her hands open, and have her place the fingers of each hand on the back of each of your hands. She should now use her fingertips to give your hands a very quick sideways push. Make sure she pushes your fists in opposite directions. Your fists will separate.

  3. Press your fists together even harder and try it again. Is it easier or harder for her to push them apart this time?

What's going on?

When you holds your fists together, you will be pressing your fists against each other using vertical forces. The vertical forces of your top hand pressing down and your bottom hand pressing up cancel each other out, balancing the forces. Balanced forces will cause objects to maintain the same state of motion (in this case, rest). Your vertical forces push only up and down. Your child pushes sideways. Since your hands are applying vertical forces, you can't balance out the horizontal finger force, and your hands slide off each other. The harder you try to hold your fists together, the easier it is to do!

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