Equilibrium - Weight

1. Jul 2, 2008

hello,

I am an art student and need help for a project I am doing. I do performance art, and I realized time and time again that performance is all about physics. Especially in this case, because I am using my own body and my general safety is involved.

I have built a stool 2.5 meters high, 50 cm squared. I want to sit on this stool during a sound art exhibition. The work is about finding a state of equilibrium, as I will be a live addition to the exposition and add to the main composition of sound elements.

I weigh around 60 kilos. If I were to build a cement base for the stool how heavy would it have to be? And which circumfrence would it need to remain stable??

Another option would be to build the stool onto a metal plate that is 1.5 meters squared. Does any one have another idea?

I would appreciate your help on this.

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2. Jul 2, 2008

Andy Resnick

You will remain safely perched on the stool if the center of mass of you plus the stool plus the base remains above the area of the base.

I assume here you know what "center of mass" means. You should have an intuitive idea of the above rule based on your own experience- balancing on one foot while holding different poses, for example.

There's two approaches to increase the stability- one is it lower the center of mass, by making a really heavy base (that would be the cement). The other approach is to increase the area of the base- the metal plate.

Let's say the stool weighs 20 kilos, and let's say when you sit, your center of mass is centered on and located at the seat. This puts the center of mass of you plus the stool is located about 2.2 m off the floor- fairly high. This means if you lean 6.5 degrees off (the stool is 50 cm on a side), you will fall off.

If your cement base weighs as much as you, the COM is back down to 1.25 m, and a lean angle of 12 degrees is the limit. But then the stool weighs 80 kilos. Adding the metal plate (thick enough so it does not flex) instead means you can lean out about 20 degrees.

So, as long as the construction is sturdy, I would go with the metal plate. And be careful climing up and down the thing.

3. Jul 2, 2008

tiny-tim

Welcome to PF!

Hi naaaadia ! Welcome to PF!

If the base was a shallow enough curve, it would wobble a bit but still return to equilibrium.

Shouldn't everything in a sound exhibition wobble a bit?

If the base was smooth enough, the person sitting inside the egg could even get it to spin.

4. Jul 2, 2008