Where does the energy to create tides come from?

In summary, the gravitational pull of the sun and the moon cause the tides. The energy to create and move the tidal bulge comes from the Earth's rotation, which is being dissipated by slowing the Earth's rotation.
  • #1
Jahn89
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Hi, I wonder if any of you can help, probably a very simple answer, but here goes...

The gravitational pull of the sun and the moon cause the tides, correct? I also understand that energy cannot be created or destroyed, also correct?
Since the orbit of both the sun and the moon are constant, i.e not decreasing in radius or speed,and the mass of both could be assumed to be fairly constant I would assume no energy is being taken from these systems.
Therefore my question is, where does the energy come from to move the seas and oceans?

Thanks
 
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  • #2
The energy is coming from the Earths rotation. Tidal friction is causing the Earths rotation (about it's own axis) to slow and hence for the length of a "day" to gradually increase.
 
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  • #3
Right answer to the wrong question. The energy is being dissipated by slowing the Earth's rotation but the op is asking where the energy is coming from. And the answer is that it is stolen from the moon's orbital energy.
 
  • #4
russ_watters said:
Right answer to the wrong question. The energy is being dissipated by slowing the Earth's rotation but the op is asking where the energy is coming from. And the answer is that it is stolen from the moon's orbital energy.
No. The action of the tides actually causes energy to be transferred from the Earths rotational energy to the moons orbital energy. Because the Earth rotates faster (lower period) than the moon orbits it causes the tidal bulge to always move slightly ahead of the line joining the Earth and moon centers. This in turn causes the gravitational pull to be between the Earth and moon to have both a radially directed and also a small orbitally directed component (due to the slight "dumbell" shape of the Earth with tides). The orbitally direct component provides a drag on the Earth's rotaton and at the same time actually imparts orbital energy to the moon.

So the net effect is that the Earth is losing rotational energy and some of that energy is being transferred into the moons orbit, but only a relatively small proportion as the tidal system is a very lossy process so that most of the energy is just lost as heat in the tidal system.
 
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  • #5
Jahn89 said:
Hi, I wonder if any of you can help, probably a very simple answer, but here goes...

The gravitational pull of the sun and the moon cause the tides, correct? I also understand that energy cannot be created or destroyed, also correct?
Since the orbit of both the sun and the moon are constant, i.e not decreasing in radius or speed,and the mass of both could be assumed to be fairly constant I would assume no energy is being taken from these systems.
Therefore my question is, where does the energy come from to move the seas and oceans?

The answer that Uart gave in this thread is correct.

There is one other scenario that is interesting to explore. What if both the primary and the satellite spin at the same rate as the orbit around the common center of mass?
In that scenario there is no dissipation of energy, so no source of energy is involved.

The state of spin rate identical to orbit rate is called 'tidal lock'. And in fact our Moon is in tidal lock. (More precisely: the Moon orbit is somewhat eccentric, so the Moon orbit angular velocity fluctuates accordingly. The Moon spin rate is constant, so as seen from the Earth the Moon is kind of "shaking its head".)Finally, a thought demonstration. What if you bring two celestial bodies from great distance to each other, setting them up in orbit around each other, with both celestial bodies in tidal lock. In the final state the two celestial bodies are tidally distorted. What provided the energy for that distortion away from spherical shape? The answer must be that when two celestial bodies distort each other tidally (while in tidal lock) then gravitational potential energy is the energy source. In distorting each other tidally the two celestial bodies must move a little closer to each other, thus releasing gravitational potential energy.

Cleonis
 
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uart said:
No. The action of the tides actually causes energy to be transferred from the Earths rotational energy to the moons orbital energy.
Dang, I always get that part wrong. Sorry. So energy is transferred from the Earth's rotation to the Moon's orbit and in the process some (29/30ths according to the wiki) is lost to friction.

Still, I think what the OP is wondering is where the energy to create/move the tidal bulge itself comes from (and I still didn't answer it right...). In other words, the friction doesn't cause the bulge to move, it causes the bulge to slow down. So what causes it to move? Answer is that there is no energy associated with causing the moving of the bulge. It is a essentially a standing wave and it was created when the moon was created/entered into orbit and would move around the Earth forever the same way if there were no friction.
 
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FAQ: Where does the energy to create tides come from?

1. What is the main source of energy for creating tides?

The primary source of energy for creating tides is the gravitational pull of the moon on the Earth's oceans. This gravitational force causes the water in the oceans to bulge towards the moon, creating high tides on the side of the Earth facing the moon and low tides on the opposite side.

2. Do other factors besides the moon's gravity contribute to tidal energy?

Yes, the sun also plays a role in creating tides. Although the sun's gravitational pull is much weaker compared to the moon's, it still has an influence on the tides. When the sun, moon, and Earth are aligned, their combined gravitational pull creates higher high tides and lower low tides, known as spring tides. When the sun and moon are at right angles to each other, their gravitational pull partially cancels out, resulting in lower high tides and higher low tides, known as neap tides.

3. How does the Earth's rotation affect tidal energy?

The Earth's rotation also plays a role in creating tides. As the Earth rotates, the bulges of water caused by the moon's gravitational pull move around the Earth, resulting in two high tides and two low tides every day. The exact timing and height of the tides vary depending on the location and topography of the coastline.

4. Can variations in the moon's orbit affect tidal energy?

Yes, the moon's orbit is not a perfect circle, so its distance from the Earth can vary. When the moon is at its closest point to Earth (perigee), its gravitational pull is stronger, resulting in higher high tides and lower low tides. Conversely, when the moon is at its farthest point from Earth (apogee), its gravitational pull is weaker, resulting in lower high tides and higher low tides.

5. Are there any other factors that can impact tidal energy?

Yes, there are other factors that can affect tidal energy, such as the shape and depth of the ocean floor, the shape of the coastline, and the strength and direction of wind and ocean currents. These factors can cause localized variations in tidal patterns and make predicting tides more complex.

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