A rock sitting on land, the ocean floor, or floating in space maintains its shape somehow. Gravity isn't keeping it together because it is too small, so I'm assuming it is chemical or nuclear bonds keeping it together as a solid. If not it would simply crumble apart. So, what type of energy maintains the shape of a rock, where did this energy come from, and is it slowly dissipating?

As a corollary, if a large rock is placed on top of a small rock, is the energy required to maintain the shape of the small rock 'used' at a greater rate?


5 Answers 5


No, the exact opposite is true.

The molecules in a rock don't stay together because they're spending energy. They stay together because of attractive chemical bonds. The molecules have lower energy when they're together than when they're not, so you have to spend energy to break the rock apart, not to keep it together.

  • 1
    $\begingroup$ From where does the energy come for the chemical bonds? Isn't "attractive chemical bonds" an exchange of electrons? Is this exchange lossless? $\endgroup$
    – CramerTV
    Commented Nov 30, 2018 at 23:14
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    $\begingroup$ Where does the energy come from to roll downhill? There's an absolute potential energy at the bottom of the hill. Why doesn't it just roll uphill after a while sitting at the bottom when the energy runs out? $\endgroup$ Commented Dec 1, 2018 at 0:13
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    $\begingroup$ I'm not being snarky either. This is an exact analogy using gravity and macro matter contours instead of electric forces and bond shapes. $\endgroup$ Commented Dec 1, 2018 at 0:14
  • 4
    $\begingroup$ @CramerTV A chemical bond doesn't consist of firing electrons back and forth. It's simply the fact that electrons have some energy when they're bonded, and some energy when they're not, and the former is lower. $\endgroup$
    – knzhou
    Commented Dec 1, 2018 at 9:52
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    $\begingroup$ @CramerTV Unfortunately, almost every pop science source explains forces in this fake way because it's easier -- the real explanation is just too technical. There is no need for the firing and refiring of photons to be "lossless", because it doesn't actually happen, at all. $\endgroup$
    – knzhou
    Commented Dec 3, 2018 at 18:36

There are various mechanisms that keep solid things together, they all have one thing in common: They reduce energy to a minimum! When you want to break it apart, it costs you energy to do so!

Examples of bonds are:

Hydrogen-Bonds, which are very weak and come from an asymmetry of the electron around the proton, in such a way that it is energetically favourable to form bonds instead of repel each other.

Ion-bonds, which can be quite strong, but the materials are often recalcitrant (brittle). Materials having ion-bonds are not pure, they are a mixture of two different elements, one positively charged, another negatively charged and they form molecules together, mainly due to the Coulomb force.

There are many more!


The amount of work done is equal to the distance moved times the force in the direction of motion. As the rock is staying the same shape it does not need to exert energy.

You may be thinking that the rock needs to expend energy in order to hold up its heavy mass in the same way our muscles do if we hold up a heavy weight. But muscles need to contract to lift a heavy weight and this requires continuous activity at the cellular level as explained in the answer to this question.


Consider an answer by contradiction:

Imagine the rock is in the vacuum of outer space with no energy able to be added to it. Suppose it does use energy to maintain shape. Then at some point, it will run out of energy and the shape will change. Now, since it is out of energy and can't change shape, isn't it now maintaining shape without energy?


Once there was a paradox in physics: why electron doesn't fall "down onto" atom's kernel and they decided it was "rotating". But "rotating" it would emit radiation and thus would loose energy. So later then they decided that "rotating" electron looses no energy staying on its "enabled orbits" and only would emit radiation when changing orbits.

The rock is a "set" of atoms, actually. You should look into the root of things.

Gravity isn't keeping it together because it is too small

Gravity is huge on small distances (look up the canonical formula — it's having /R^2, actually). But it's being compensated by other forces. We might continue this for long, but obviously there's no reason to repeat well known sources: https://en.wikipedia.org/wiki/Fundamental_interaction

Back to your q-n: rock is a collection of atoms. Atoms poses colossal energy indeed but as electrons on theirs orbits don't loose theirs energy and there's no intensive radioactive decay occurring it's all being "more or less" balanced. And when it's balanced — you guess it.

  • $\begingroup$ Electrons in atoms don't really move in orbits, like planets orbiting a star. There are energy levels called orbitals, but it's misleading to think of an electron in an orbital moving with a classical trajectory, where at any given moment the electron has a definite position and a definite momentum. $\endgroup$
    – PM 2Ring
    Commented Dec 4, 2018 at 3:41
  • $\begingroup$ Is light a wave or not? :) All those things are actually abstractions and in my explanation I've given abstractions that use "planet model of atoms". It doesn't mean if you scale your microscope you'd really see balls around balls. It's pretty obvious what you're saying $\endgroup$
    – poige
    Commented Dec 4, 2018 at 4:39
  • $\begingroup$ That's, BTW, why some parts of mine answer are quoted like "down onto", and "rotating". It's not the essence actually but it helps in my opinion to come up with understanding of stability the overall system has and why it's considered stable. $\endgroup$
    – poige
    Commented Dec 4, 2018 at 4:43

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