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# Why would object appears weightless if earth spins faster

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1. Thx

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2. Do you have a surrounding question, or any data to go with this? What is the exact question you're asking, or is it purely out of interest?

Context is key!
3. (Original post by SillyEddy)
Do you have a surrounding question, or any data to go with this? What is the exact question you're asking, or is it purely out of interest?

Context is key!
Lol. Sorry. Why would the object become weightless if the earth spins faster.

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4. (Original post by xiyangliu)
Lol. Sorry. Why would the object become weightless if the earth spins faster.

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Thats the question.

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5. Imagine the earth spinning faster and faster and faster .....

At some stage your feet would lift off from the surface of the Earth - which force do you think would try to push you off and what force would try to keep you on the Earth?
6. (Original post by Charries)
Imagine the earth spinning faster and faster and faster .....

At some stage your feet would lift off from the surface of the Earth - which force do you think would try to push you off and what force would try to keep you on the Earth?
I am guessing gravity will try to keep u on the earth. But which force will push u off ??

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7. Centripetal force?
8. (Original post by Vian)
Centripetal force?
But that has the same direction of the gravitational force ?

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9. (Original post by xiyangliu)
But that has the same direction of the gravitational force ?

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You first need to be clear what you mean by "appear weightless" before you can explain how this might happen.

What do you mean by the term "weightless"?
10. (Original post by Stonebridge)
You first need to be clear what you mean by "appear weightless" before you can explain how this might happen.

What do you mean by the term "weightless"?
Apparently the gravity cancels out the centrifugal force when the earth rotates really fast. ?

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11. (Original post by xiyangliu)
Apparently the gravity cancels out the centrifugal force when the earth rotates really fast. ?

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You still haven't defined "weightless".
If you do this you can then say what conditions are required to produce it.
The main problem with this topic is that there is generally not a clear understanding of what the word means.
12. (Original post by Stonebridge)
You still haven't defined "weightless".
If you do this you can then say what conditions are required to produce it.
The main problem with this topic is that there is generally not a clear understanding of what the word means.
Hm.... Sorry abt that.
Hm... what would happen to any object on this planet's equator if earth rotates faster and faster ? Would their gravitational force cancel out with the centrifugal force ? I am actually quite confused at the moment.. My mind is in a state if chaos at the moment ....

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13. (Original post by Stonebridge)
You still haven't defined "weightless".
If you do this you can then say what conditions are required to produce it.
The main problem with this topic is that there is generally not a clear understanding of what the word means.
And yes under what condition It happens and why does it happen. ?

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14. Ok, so the earth is rotating with angular speed w, and the radius of the earth is r. Suppose we have our object sitting on the scales on the surface of the earth:

http://cosketch.com/Saved/prCZAiM5

There are two forces acting on the object. The weight force and the force P which is the scales pushing up on the object. The value of P will be used to determine the reading on the scales.

In order for the object to keep on rotating with the earth, the net force on it must m*(w^2)*r which is the centripetal force.

Therefore, mg - P = mw^2r so P = mg - mw^2r so increasing the speed of rotation will decrease P and hence decrease the reading on the scales, so the object would appear to weigh less if you were to try to weigh it.
15. (Original post by ttoby)
Ok, so the earth is rotating with angular speed w, and the radius of the earth is r. Suppose we have our object sitting on the scales on the surface of the earth:

http://cosketch.com/Saved/prCZAiM5

There are two forces acting on the object. The weight force and the force P which is the scales pushing up on the object. The value of P will be used to determine the reading on the scales.

In order for the object to keep on rotating with the earth, the net force on it must m*(w^2)*r which is the centripetal force.

Therefore, mg - P = mw^2r so P = mg - mw^2r so increasing the speed of rotation will decrease P and hence decrease the reading on the scales, so the object would appear to weigh less if you were to try to weigh it.
Ok.. What is this force P ? Is it the reaction force? Sorry if this question is stupid. My mind is in a state of chaos at the moment ..

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16. (Original post by xiyangliu)
Ok.. What is this force P ? Is it the reaction force? Sorry if this question is stupid. My mind is in a state of chaos at the moment ..

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Yes it is. It's also used by the scales to determine the reading to display (for instance if it was a spring-operated scales then increasing P would increase how much the spring is pushed/stretched and the reading can be determined from there)
17. (Original post by ttoby)
Yes it is. It's also used by the scales to determine the reading to display (for instance if it was a spring-operated scales then increasing P would increase how much the spring is pushed/stretched and the reading can be determined from there)
I see. So increasing in speed rotation suggests increase in the frequency of the rotation and w increases because that P=mg- mrw^2, so that P decreases

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18. (Original post by xiyangliu)
I see. But why increasing in speed of rotation would increase in magnitude of Force P ?

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No, go back to post 14 - increasing the speed of rotation would decrease P.

I was talking about how changing P would change the reading on the scales.
19. (Original post by ttoby)
No, go back to post 14 - increasing the speed of rotation would decrease P.

I was talking about how changing P would change the reading on the scales.
Sorry. I realised that just now so I just re edited my previous post

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20. (Original post by ttoby)
No, go back to post 14 - increasing the speed of rotation would decrease P.

I was talking about how changing P would change the reading on the scales.
I think I get it now. Thx

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