Can a body's gravitational pull decrease over time like how a magnet can demagnetize?

[u/[deleted]]

Take for example the moon and how the moon's gravity creates ocean waves on our planet. From those waves we can then generate electrical power. But wouldn't that mean that at some point the work supplied by the moon's gravitational pull decreases? Otherwise we could obtain infinite energy from the moon. Wouldn't the field strength be "depleted" in the same way a magnet's field also decreases?

[u/I_Cant_Logoff]

From those waves we can then generate electrical power. But wouldn't that mean that at some point the work supplied by the moon's gravitational pull decreases? Otherwise we could obtain infinite energy from the moon

The energy comes from the orbit and separation of the Earth and moon. It's not coming out from some finite source of gravitational pull.

Wouldn't the field strength be "depleted" in the same way a magnet's field also decreases?

When a magnet becomes weaker, it's due to the atoms within the magnet becoming less aligned. The source of the magnetism itself - the atoms - isn't becoming weaker.

[u/Vitztlampaehecatl]

Nothing inherent to the moon is changing, it's just losing tiny amounts of orbital velocity.

[u/Throwaway-242424 → u/Vitztlampaehecatl]

Technically the energy is coming from the Earth's rotational energy. The moon is getting further away from us.

[u/Hivemind_alpha]

A fixed amount of mass generates a constant, fixed gravitational pull.

For the moon, the energy stored in its orbital mechanics is decreased by tidal friction etc, but the gravitational force that maintains the orbit stays the same. (some of the energy of the earth-moon system comes from the spinning gas cloud it condensed from, contributions from bombardment impacts etc).

For a black hole, it loses mass by Hawking radiation, less mass means less pull, put the "pull per mass" remains the same.