<blockquote>
  <p>Where does the power/energy go?</p>
</blockquote>

<p>It goes into heating the Earth and the Moon. That heat in turn spreads out into the universe.</p>

<p>While the Earth-Moon system comes very close to conserving angular momentum, it does not conserve mechanical energy. In fact, that angular momentum transfers from the Earth's rotation to the Moon's orbit means that the total mechanical energy of the Earth-Moon system is necessarily reduced. Mechanical energy is only conserved in isolated, non-dissipative systems. The tides in the Earth's oceans, in the Earth as a whole, and in the Moon as a whole means that the Earth-Moon system is dissipative.</p>

CC BY-SA 4.0
2024-06-05T12:35:03.173Z
So tidal friction really is friction, and ultimately it results  in heat?
Miss Understands
CC BY-SA 3.0
2016-09-03T07:14:28.817Z
2016-09-03T07:14:28.817Z
David Hammen
<p>You're correct in assuming the net angular momentum of the system in question here will remain constant. The Moon's orbit around Earth is responsible for the slowing of Earth's rotation. This effect is <em>extremely</em> small. </p>

<p>The decrease in Earth's angular momentum is transferred to the moon, which resultantly sees it's orbit accelerate. This acceleration also causes the moon to move further and further from the Earth. This trend will continue until they reach a common speed.</p>

CC BY-SA 3.0
2016-09-02T18:12:45.990Z
And orbital dynamics mean that as the Moon is accelerated it moves to a higher orbit and so actually slows down.
James K
CC BY-SA 3.0
2016-09-02T22:31:05.297Z
The [answer by Brumder](http://astronomy.stackexchange.com/a/18195) is correct, but forgets to mention that some of the orbital and rotational energy is transformed into heat via friction, which is called [tidal heating](https://en.wikipedia.org/wiki/Tidal_heating).
Ebonair
CC BY-SA 3.0
2016-09-03T01:29:08.297Z
+1, but strictly speaking this is an answer to "where does the angular momentum go" rather than "where does the power/energy go" as in the OP. This answer could be improved by mentioning that the kinetic energy in the system ultimately becomes heat, which happens because tidal forces flex the Earth and its oceans, which generate heat by moving against each other, and that's ultimately what causes the change in rotation speed.
N. Virgo
CC BY-SA 3.0
2016-09-03T03:31:32.947Z
It might help to clarify that the acceleration mentioned herein is a nominal result assuming all else remained equal, but as the orbit of Luna enlarges the actual orbital speed (both linear and angular) is *reduced*. The energy goes into increased potential energy in the Earth-Moon system as well as into heating (the potential energy gain is twice the loss of orbital kinetic energy, after all).
dmckee --- ex-moderator kitten
CC BY-SA 3.0
2016-09-02T17:34:31.387Z
2016-09-02T17:34:31.387Z
Brumder
<p>I understand from Wikipedia that, "The length of the day, which has increased over the long term of Earth's history due to tidal effects, ...".  If the angular velocity of the earth is decreasing then the stored rotational energy is decreasing.  Where does the power/energy go?</p>

CC BY-SA 3.0
2016-09-02T20:14:08.027Z
Is there also some energy lost as the earth "stretches" to become more round?
IQAndreas
CC BY-SA 3.0
2016-09-03T03:32:35.173Z
As a matter of vocabulary, "power" isn't a conserved quantity and one doesn't have to account for where it goes. Energy is conserved and has to be accounted.
dmckee --- ex-moderator kitten
<earth><rotation>
Decreasing rate of Earth's rotation: where does the power go?
scorpdaddy
# Decreasing rate of Earth's rotation: where does the power go?

(Asked by: username_0 on 2016-09-02)

I understand from Wikipedia that, "The length of the day, which has increased over the long term of Earth's history due to tidal effects, ...". If the angular velocity of the earth is decreasing then the stored rotational energy is decreasing. Where does the power/energy go?

**Tags:** earth, rotation

> **Comments:**
> **username_1**: Is there also some energy lost as the earth "stretches" to become more round?  
> **username_2**: As a matter of vocabulary, "power" isn't a conserved quantity and one doesn't have to account for where it goes. Energy is conserved and has to be accounted.  

---

## 2 answers

### Answer by username_5 on 2016-09-02. Score: 13 | Accepted answer

You're correct in assuming the net angular momentum of the system in question here will remain constant. The Moon's orbit around Earth is responsible for the slowing of Earth's rotation. This effect is *extremely* small.

The decrease in Earth's angular momentum is transferred to the moon, which resultantly sees it's orbit accelerate. This acceleration also causes the moon to move further and further from the Earth. This trend will continue until they reach a common speed.

> **Comments:**
> **username_6**: And orbital dynamics mean that as the Moon is accelerated it moves to a higher orbit and so actually slows down.  
> **username_7**: The [answer by username_5](http://astronomy.stackexchange.com/a/18195) is correct, but forgets to mention that some of the orbital and rotational energy is transformed into heat via friction, which is called [tidal heating](https://en.wikipedia.org/wiki/Tidal_heating).  
> **username_8**: +1, but strictly speaking this is an answer to "where does the angular momentum go" rather than "where does the power/energy go" as in the OP. This answer could be improved by mentioning that the kinetic energy in the system ultimately becomes heat, which happens because tidal forces flex the Earth and its oceans, which generate heat by moving against each other, and that's ultimately what causes the change in rotation speed.  
> **username_2**: It might help to clarify that the acceleration mentioned herein is a nominal result assuming all else remained equal, but as the orbit of Luna enlarges the actual orbital speed (both linear and angular) is *reduced*. The energy goes into increased potential energy in the Earth-Moon system as well as into heating (the potential energy gain is twice the loss of orbital kinetic energy, after all).  

---

### Answer by username_3 on 2016-09-03. Score: 10

> Where does the power/energy go?

It goes into heating the Earth and the Moon. That heat in turn spreads out into the universe.

While the Earth-Moon system comes very close to conserving angular momentum, it does not conserve mechanical energy. In fact, that angular momentum transfers from the Earth's rotation to the Moon's orbit means that the total mechanical energy of the Earth-Moon system is necessarily reduced. Mechanical energy is only conserved in isolated, non-dissipative systems. The tides in the Earth's oceans, in the Earth as a whole, and in the Moon as a whole means that the Earth-Moon system is dissipative.

> **Comments:**
> **username_4**: So tidal friction really is friction, and ultimately it results  in heat?  

---

