system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are you able to jump higher when running than when standing still?

Please, explain it to me like I'm 5.
gpt
It takes no effort to redirect momentum.

A ball hitting a 45° slope will bump up. Yet the ball has no muscle!

You intuitively know that, and you will put your leg almost 45°forward so that your forward momentum get converted to upward momentum by simply keeping your leg straight.

But because you have muscle, you can actually use them to add even more jump. So instead of keeping your leg straight, you bend them then stretch them with strength. Not only does it redirect your momentum, but you add even more.

If you don't have speed, all you can do is use your strength to jump.

Note that preserving momentum is easier than creating it. If we had wheels it would be almost free. See "humans with wheel" on Wikipedia (aka. cyclist).