Sun tides and tidal torque on the earth

[Andrew Mason]

It is said that the moon's tidal forces on the Earth create differential torque which causes a slowing of the Earth rotation. It is said that this causes the moon to increase its radius of orbit. The remarkable result is that rotational energy of the Earth is transferred to the moon to increase its gravitational potential. I am not sure how that is accomplished (so far I have not found a convincing explanation of this yet) but let's say it is true.

Since the sun also exerts a tidal force on the earth, does the sun not cause the Earth to slow its rotation as well? If so, what is the earth/sun response to this in order to conserve angular momentum? Does this cause the Earth to increase its radius of orbit around the sun, over time?

AM

 

[Andre]

This figure gives the scholar traditional explanation for tidal drag and the reason why the moon steals rotational energy from Earth. Source

However, there are probably several complications, like an increased distance of the moon would decrease it's orbit time and hence it's tidal locked rotation.

For the sun there is no difference in mechamism, but the forces are considerably weaker.

 

[ravenprp]

Thank you for bringing up this interesting topic. The concept of tidal forces and torque on the Earth due to the moon and the sun is something that has been studied and debated by scientists for centuries. To address your questions, let's first understand the basics of tidal forces and torque.

Tidal forces are the result of the gravitational pull exerted by one object on another. In the case of the Earth and the moon, the moon's gravitational pull on the Earth causes the Earth's oceans to bulge towards the moon, creating the familiar high and low tides. This same force also creates a slight bulge on the opposite side of the Earth, away from the moon. This is known as the tidal bulge.

Now, torque is the force that causes an object to rotate. In the case of the Earth and the moon, the tidal bulge created by the moon's gravitational pull exerts a torque on the Earth. This torque is what causes the Earth's rotation to slow down, as you mentioned. This slowing of the Earth's rotation results in a transfer of rotational energy from the Earth to the moon, causing the moon's orbit to increase in radius.

Now, to address your question about the sun's tidal forces and torque on the Earth. It is true that the sun also exerts a tidal force on the Earth, but it is much weaker compared to the moon's tidal force. This is because the sun is much farther away from the Earth compared to the moon. However, the sun's tidal force does contribute to the Earth's slowing rotation, albeit to a much smaller extent.

To conserve angular momentum, the Earth's response to the sun's tidal force is to increase its distance from the sun. This is known as tidal acceleration. However, this increase in distance is very small and cannot be observed over a human lifetime. It is estimated that the Earth's distance from the sun increases by about 1.5 centimeters per year due to tidal acceleration.

In conclusion, both the moon and the sun's tidal forces and torque do contribute to the Earth's slowing rotation, but the moon's effect is much stronger. The Earth's response to this is to transfer rotational energy to the moon and increase its distance from the sun through tidal acceleration. I hope this helps clarify the concept for you.