Seesaw Science

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Question about balance. If I have a seesaw that’s perfectly balanced on a fulcrum and it’s perfectly level, it will stay balanced with both sides in the air. However, if I tip one side of the seesaw toward the ground, the seesaw will begin to fall in that direction. Why does it do that even though the weight on each side hasn’t changed? Or has it?

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It will do that if it is unstable at the equilibrium point. If it has handles and seats above the bar, then the weight of those (and thus the center of gravity) shifts towards the lowered side.

You can see in this toy an example of the center of gravity being lower, and the balance being stable as the weight shift of CG *corrects* a disturbance: [https://i.imgur.com/HhhsatH.jpg](https://i.imgur.com/HhhsatH.jpg)

It depends on how the beam is mounted to the piviot.

Usually, the beam is mounted above the piviot, and brackets on the bottom of the beam wrap around the piviot. In this configuration, the strength of the beam is relied on to support itself, while the brackets have an easier job of only keeping the beam from sliding off one side of the piviot.

In another configuration, the beam can be mounted below the piviot. Brackets will have a much greater job of supporting the full weight of the beam and keeping it secured. Usually, this isn’t done. The brackets are more likely to fail than the beam, and much larger brackets would be required.

A beam mounted above the piviot has a higher center of mass and moves towards the direction of gravity when it’s tilted. Imagine a tall bracket that holds the beam far above the piviot if this helps. The seesaw would look like the letter T.

I think the easiest way to understand this is with Newtons first law of motion.

An object will stay at a constant velocity unless acted upon by an unbalanced force.

Imagine we pushed a box in space. There isn’t any air resistance to slow it down so it will just go on for ever and ever, because there is no force stopping it.

The same thing is happening with a balanced see saw. When left alone it has no unbalanced force applied to it so it is moving at a constant speed, that speed happens to be zero. But the. You push it, providing an unbalanced force and changing it’s velocity. But the moment it leaves your hand a force is no longer applied to it, and so it will move at a constant velocity. It’s just this velocity is now not zero. If there was no air, and no ground to get in the way it would just keep spinning like the when you push a box in space.