In sports, they say “put the centre of gravity in the knees”.

Not only a person can change its centre of gravity but even a cat — to always land on all its legs, it uses its tail among other things.

The position of the centre of gravity depends on the distribution of weight in the body and its shape.

The centre of gravity is usually in the geometric centre of the body but only under the condition that the body is homogeneous which means, it has the same density everywhere.

The effect of weight distribution can be clearly seen with a water bottle — when it’s full, it’s in the middle, the less water there is, the more it moves to the bottom.

But a human (or a cat) cannot move the matter of which they are composed, but they can change their shape.

If we imagine a plasticine cylinder, the centre of gravity is in its centre.

But if we transform the cylinder into a ring, the centre of gravity will be in the middle of the ring — which means, outside the plasticine.

The mentioned “move” of the centre of gravity to the knees is related to stability — the lower our centre of gravity, the more stable we are (more push is needed to fall over).

By changing our shape (instead of standing upright with our feet together) we will have a lower centre of gravity, plus we have a wider area to stand on (we spread our legs).

In the case of gymnastics (which I can describe rather theoretically), we can get the centre of gravity outside our body during the “bridge” or if we touch the mat with our hands.

Another example is a high jump — because the jumper curves, his centre of gravity is under the bar, even though his body is above it.

So we can move the centre of gravity but the given instruction “centre of gravity to the knees” is more important to increase our stability.