Since gravity can do work, where is the energy coming from?

Question

For example, the gravity causes the tides and that can be harnessed as an energy source. So where is the energy coming from?

You say the tides come from kinetic energy, but the kinetic energy still comes from gravity.

Answer 1

Space time curvature?

Answer 2

i can answer both of the questions you ask. the energy for gravity comes from the fact that mass is energy and that gravity is the result of this. as said by an above answer this causes a curve in the space/time continium, i could say more, but that take you all night to even Read let alone comprehend. suffice to say its complex.

to your other question. we can and are going to harness the energy of the tides, wich is kinetic energy, or the energy of motion. the energy comes from the pull of the moon on the water, the most pliable and abundant rescorce on earth, this moves the water. imparting kinetic energy on it.

Answer 3

Gravitational energy basically comes from the potential energy of the gravitational field. But the tide question is more interesting; the tidal flow comes from the kinetic energy of the earth's rotation. Which is why the speed of rotation is gradually decreasing (days getting longer) and the moon is moving away from the earth at about an inch a year.

Answer 4

Gravity does not cause tides in the sense you mean here. The motion of the moon causes tides (transmitted by gravity). When you take energy from tides you are in fact taking kinetic energy from the moon. But it has a lot to spare.

Answer 5

No, gravity is a conservative force. It does no work. You can't get more energy out of it than you put in - for example, yes, it will cause a ball to fall out of the sky, but first you have to get the ball up there. That required work.

Answer 6

Anything in free fall in a gravitational field had to placed at an elevated level, it contains potential energy.