No, the dumbbell-on-a-table is not using any energy to keep from falling down. What takes energy, in general, is not exerting a force but moving things against an opposing force. Getting the dumbbell up into the air takes energy; letting it fall again will release some energy; but that’s a one-off, and there isn’t any ongoing energy cost to keeping it in the same place.
(Why does the stuff on the surface of the earth not all fall inward and the earth collapse into a black hole? Because as well as the inward force those things experience due to gravity, there are also outward forces, mostly arising from electrostatic repulsion between the electrons on nearby atoms, and when something is sitting motionless on the ground that’s because those forces balance one another. This is also what’s happening to the dumbbell on the table.)
So maybe the real question here is not “how can the table hold the dumbbell up without expending energy?”, but “how come my arm needs to use energy to hold the dumbbell up?”. The answer to that is: while there are structures, like a table, that can hold a dumbbell up without using energy, your arm is not built one of them: because it’s made from flexibly-articulated bits, and it’s only able to achieve the same effect the table can by less efficient means. (But in exchange for that it gets the ability to do things the table can’t, like moving the dumbbell around.)
Something about this seems not right, but I don’t know enough to be sure if my intuition means anything. There’s no energy cost to holding things apart? Surely heat is slightly higher than it’d be in lower gravity?
No, the dumbbell-on-a-table is not using any energy to keep from falling down. What takes energy, in general, is not exerting a force but moving things against an opposing force. Getting the dumbbell up into the air takes energy; letting it fall again will release some energy; but that’s a one-off, and there isn’t any ongoing energy cost to keeping it in the same place.
(Why does the stuff on the surface of the earth not all fall inward and the earth collapse into a black hole? Because as well as the inward force those things experience due to gravity, there are also outward forces, mostly arising from electrostatic repulsion between the electrons on nearby atoms, and when something is sitting motionless on the ground that’s because those forces balance one another. This is also what’s happening to the dumbbell on the table.)
So maybe the real question here is not “how can the table hold the dumbbell up without expending energy?”, but “how come my arm needs to use energy to hold the dumbbell up?”. The answer to that is: while there are structures, like a table, that can hold a dumbbell up without using energy, your arm is not built one of them: because it’s made from flexibly-articulated bits, and it’s only able to achieve the same effect the table can by less efficient means. (But in exchange for that it gets the ability to do things the table can’t, like moving the dumbbell around.)
Something about this seems not right, but I don’t know enough to be sure if my intuition means anything. There’s no energy cost to holding things apart? Surely heat is slightly higher than it’d be in lower gravity?