Activity: Balance and Centre of Mass

On SCOPE's boardsports episode, you saw Bronte and Christina do some pretty neat experiments about balance. Here's what they did. Watch the clip.

Bronte and Christina about to touch their toes.

What you need

• A friend
• A wall

Getting Started

Put one finger in the side of your waist and one finger in your belly button. If these two fingers were to meet inside you - they would meet at your centre of mass!

What to do

1. Stand on one foot, and have someone try and push you off balance.
2. Now stand on two feet, spread wide like a sumo wrestler, and have them try to push you again.

1. Ok, new experiment. Stand back to back with your friend, heels touching, and then both of you try and touch your toes at the same time.
2. Did just one of you fall forwards?
3. Try the same thing with your heels against a wall.
4. Is it possible to stand upright with both feet tight against a wall?  

What's happening?

Being balanced is all about your centre of mass and where it is in relation to your feet. Everyone has a centre of mass, and, in the getting started section of this activity, you found roughly where yours was.

To remain upright, our centre of mass has to be centred over our base. The base is the area touching the ground. So if you stand on one foot like a ballerina, you have to lean a little sideways so that your belly button (or centre of mass) is over the middle of your base (the one foot touching the ground). It only takes a small shove to move your centre of mass from over your base and you loose balance.

In the Sumo stance, your base is much wider, so it takes a lot of movement to get your centre of mass away from your base; and make you lose balance.

As for touching your toes, the concept is the same. As your arms move forwards to touch your toes, your bottom moves backwards so your centre of mass can remain over your base. In this activity, usually the first one to get to their toes pushes the other off balance.

With your feet in tight against the wall, you physically cannot centre your mass over your base. You just can't do it. Unless you hang on! To be a good board rider you have to have great control of your centre of mass. That's how all board riders stay upright - surfers, skateboarders, windsurfers, kiteboarders, and why they have such good balance.