# Why do we rotate along with the earth?

• HomogenousCow
In summary, the conversation discusses the factors that contribute to our rotation with the Earth. It is stated that friction and gravity both play a role in keeping us in place and moving with the Earth. However, it is also mentioned that if we were to remove one of these factors, we would not necessarily start rotating at a different speed. The importance of our location on Earth is also emphasized, as it affects our rotation. Overall, it is concluded that both friction and gravity are necessary for us to rotate with the Earth.

#### HomogenousCow

Do we rotate along with it because of it's gravitational pull? Or is it friction?

Why do you accelerate together with a moving bus while standing in it?

Well, we are already moving with the Earth, friction allows us to accelerate in any direction without sliding and keeps us in place, and gravity keeps us pulled down to the surface.

I prefer the second answer: we have always been moving with earth, so neither friction nor gravity are required to keep us moving with the earth.

russ_watters said:
I prefer the second answer: we have always been moving with earth, so neither friction nor gravity are required to keep us moving with the earth.
The OP asks about rotation along with the Earth. You can go to the North Pole, rotate slowly againts the Earth's spin, and you are not rotating along with the Earth anymore. So you cannot generally say that everyone has been always rotating with the Earth.

HomogenousCow said:
Do we rotate along with it because of it's gravitational pull? Or is it friction?

We need both.

If we had neither, we would be attracted towards the sun which, presumably, would still have gravity.

If we only had gravity, we would watch the slippery Earth moving underneath us, but we would remain stationary.

If we only had friction, we would be projected tangentially away from the Earth into space.

A.T. said:
The OP asks about rotation along with the Earth. You can go to the North Pole, rotate slowly againts the Earth's spin, and you are not rotating along with the Earth anymore. So you cannot generally say that everyone has been always rotating with the Earth.
Ok, almost everyone -- 99.99999% of the population (estimate).

vk6kro said:
If we only had gravity, we would watch the slippery Earth moving underneath us, but we would remain stationary.
Stationary wrt what?

russ_watters said:
Stationary wrt what?

With respect to the center of the earth.

Instead of being rotated, we would just be dragged towards the Earth by gravity, but we would be unable to penetrate the earth, so we would just cling to the outside, but not rotate with it.

It would be a fairly terrifying existence as we would be unable to even drill holes in the Earth to get a grip on it because it was moving so fast.
I saw a calculation that gave the speed of the Earth's rotation, at the equator, of 1070 miles per hour or 0.297 miles per second.

Good question.

Again, all that assumes we are placed on Earth stationary wrt its rotation.

The reason I consider this caveat important is that in our daily lives, friction does not play a role in keeping us rotating with the earth. Most people asking such questions seem to think that if friction suddenly disappeared, we would start being left behind Earth's rotation.

...unless we move significantly north or south, as per A.T.'s point.

## 1. Why does the Earth rotate?

The Earth rotates because of the forces created by its initial formation. When the Earth was formed, it was a hot and molten ball of gas and dust. As the Earth cooled, its rotation sped up due to conservation of angular momentum, causing it to rotate at a speed of about 1,000 miles per hour at the equator.

## 2. How does rotation affect day and night?

The Earth's rotation causes day and night by constantly exposing different parts of the Earth to the Sun's light. As the Earth rotates, the side facing the Sun experiences daytime while the side facing away from the Sun experiences nighttime.

## 3. What is the significance of the Earth's rotation?

The Earth's rotation plays a crucial role in the planet's climate and weather patterns. It also helps regulate the Earth's temperature and helps distribute heat and moisture around the globe. The rotation also affects the length of a day and the direction of winds and ocean currents.

## 4. How long does it take for the Earth to make one full rotation?

The Earth takes approximately 24 hours to make one full rotation on its axis, which is why we have 24 hours in a day. However, due to the Earth's orbit around the Sun, it actually takes about 23 hours and 56 minutes for the Earth to complete one rotation relative to the stars.

## 5. Is the Earth's rotation constant?

No, the Earth's rotation is not constant. It is gradually slowing down due to tidal forces caused by the Moon and other factors such as the Earth's changing shape and distribution of mass. This means that the length of a day is slowly getting longer by about 0.002 seconds per century.