Center of Gravity

Check out these rock stacks - there's a great video at the end, go to the 6 minute mark to see something really cool.

Like rock Tetris

Some of these angles look impossible! It seems like there's no way that odd-shaped rock could be balancing on just one point, but there it is - these photos have not been altered in any way. The trick is to find the center of gravity.

The basic rule about center of gravity is this: if the center of gravity is supported, the whole thing is supported and balanced.

Scary.

This is part of the reason you throw your arms out to balance yourself - because as you move your arms, you change where the overall center of your gravity is. Try this: stand with your heels and butt totally against a wall and try to touch your toes. No matter how flexible or strong you are, it's impossible - most of your weight is in your torso, so when you touch your toes without the wall you HAVE to push your butt back to keep your torso over your feet:

Two ways to look unbalanced while still having your center of mass over your support (feet). (Source)

Without the ability to shift some of your weight to the back side of your feet, the weight of your torso will pull you over. Have you ever started to fall but you were able to swing your arms and move another leg to catch yourself? It's the same idea.

As the arms move, the center of gravity stays over his little feet on the rope

Your body knows its own center of gravity - I like to say that our instincts know physics better than we do.

The fundamental reason is that gravity is affecting all parts of everything - the center is really just the average of all the gravitational points.

These objects have a center of gravity in mid-air - which is why boomerangs curve!

This is also why top-heavy cars like SUV's can tip over more easily:

Some top-heavy cars add weight to the bottom to bring the center of gravity lower - making it harder to topple

So be safe with your center of gravity!

One more cool thing, this guy can do push-ups without legs by having a long board that keeps his center of gravity over his hands:

Still requires strength, but no amount of strength would make this possible without the device