Why do we rotate along with the earth?

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Discussion Overview

The discussion explores the reasons why humans and objects rotate along with the Earth. It examines concepts related to gravitational pull, friction, and the nature of motion in relation to the Earth's rotation, with a focus on theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that gravitational pull is a factor in why we rotate with the Earth, while others suggest friction plays a role.
  • A participant compares the situation to standing in a moving bus, implying that we naturally move with the Earth due to our initial state of motion.
  • Another viewpoint suggests that we have always been moving with the Earth, implying that neither friction nor gravity is necessary to maintain this motion.
  • One participant argues that if we were at the North Pole and rotated against the Earth's spin, we would not be rotating with the Earth, challenging the idea that everyone is always rotating with it.
  • It is suggested that both gravity and friction are necessary; without gravity, we would not be anchored to the Earth, and without friction, we would be projected away from it.
  • A participant questions what "stationary" means in this context, suggesting it refers to being stationary with respect to the center of the Earth.
  • Another participant emphasizes that in daily life, friction does not play a role in keeping us rotating with the Earth, and that the assumption of being stationary with respect to Earth's rotation is important.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the roles of gravity and friction in maintaining rotation with the Earth. The discussion remains unresolved, with no consensus on the necessity or sufficiency of these factors.

Contextual Notes

Some claims depend on specific assumptions about motion and reference frames, and there are unresolved questions regarding the implications of friction and gravity in this context.

HomogenousCow
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Do we rotate along with it because of it's gravitational pull? Or is it friction?
 
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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.
 
  • #10
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.
 

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