This has always puzzled me. As i stand on the earth i require energy to exert a force over gravity to enable me to keep standing. The net force between me and the the earth is zero and thus i remain standing still. However my amount of energy depletes as a result of this and will culminate in me being unable to stand as a result of the energy loss. Where does the energy for the earth come in order to apply the force of gravity between me and it. Since i appear to suffer a loss of energy what happens with respect to the earth exerting a force over me.
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I advise you to go lie down. Go on, do it. Put your back to the ground and just lie there. After a while you'll notice that you don't feel any weaker. Why? Because you haven't lost any energy.
It takes no energy to resist another force. It does take energy to apply a non-zero force to an object to do work: $$W=F\cos\theta s$$ Or, for a variable force. $$W= \int F ds$$ where $W$ is work (in units of Joules, just like energy), $F$ is force, $\theta$ is the angle between the force and the displacement, and $s$ is the displacement (with $ds$ being an infinitesimal displacement). But while you're lying down, your displacement, $s$, is zero. This means that $$W=F\cos\theta\times(0)=0 \text{ Joules}$$ It takes no energy to do no work, which, in this case, is applying a force over zero distance.
On a different note, while you're lying down (or standing up), the forces between your feet and the ground are gravity and the electromagnetic force. The electromagnetic force means that when you're standing on the ground, the atoms in your feet aren't actually touching the atoms in the ground. So you're not even the thing applying force!
HDE 226868
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The energy doesn't deplete. Sometimes it helps to think of gravity as curved space-time. That visualization might help.
Jimmy360
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