Can you touch your toes? Seems like an easy thing to do for those of us who have the flexibility.
Now, here’s the challenge. Stand with your back and your heels pressed up against a wall, and now try to touch your toes.
You can’t do it! Not without putting your hands down on the floor, you can’t. There’s a super-simple reason for this: center-of-mass.
For human beings, your center-of-mass is somewhere in your abdomen. It’s lower down for women than men, but in the abdomen region for everyone. When you typically bend down to touch your toes, you’ll notice that the upper part of your body moves forwards, while the lower part moves backwards. You do this by default, but the major reason you need to do this is so that your center-of-mass stays over a stable point: your feet!
But as soon as you prop yourself up against the wall, the lower part of your body can’t move back! So as the upper part moves forward, your center of mass moves forward. It goes from being over your heels to being over your arches to your toes, and the instant it extends out beyond your toes, you know what happens?
You begin to rotate, and once that happens, you’re going to fall, like so:
And that’s it! This is a great trick to try on children to teach them about stability. It’s also great for physics teachers to introduce torque, rotation, and center-of-mass. (And on unsuspecting coworkers to teach them about falling on their faces!)
It’s a remarkable phenomenon that such a simple thing as touching your toes would be off-limits with your heels against a wall, but there it is! Don’t believe me? Try it yourself and see what happens, but I warned you…