When you go to sleep each night in the comfort of your overstuffed mattress. Do you fall out of bed or through the mattress? Nope. In fact you just lie there like a lump of coal. That's static equilibrium.

It's static because you're not moving; lumps of coal rarely do. It's equilibrium because you are not accelerating; so all the forces acting on your tired old body add up to zero...in math talk F = SUM(f) = ma = 0 where m is your mass (put on a little weight have we?).

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