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Author Topic: When I jump up does the Earth move down?  (Read 9439 times)

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When I jump up does the Earth move down?
« on: 07/02/2009 10:54:31 »

Hello I have a Science question.

Newton's Third Law of Motion states that for every action there is an equal and opposite reaction.  According to that, when I stand on the ground and jump up, away from the Earth, then the Earth must also move an infinitesimal distance away from me.

Is this really true in practice?

I listen to your podcast while I am doing my own science!

Boston, Massachusetts U.S.

What do you think?

lightarrow

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When I jump up does the Earth move down?
« Reply #1 on: 07/02/2009 13:01:29 »

Hello I have a Science question.

Newton's Third Law of Motion states that for every action there is an equal and opposite reaction.  According to that, when I stand on the ground and jump up, away from the Earth, then the Earth must also move an infinitesimal distance away from me.

Is this really true in practice?

I listen to your podcast while I am doing my own science!

Boston, Massachusetts U.S.

What do you think?
Yes, of course is true.
P.S. Please, stop jumping, I can't keep the book still in my desk!

LeeE

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When I jump up does the Earth move down?
« Reply #2 on: 07/02/2009 17:19:48 »
In practice, you'll just make a local deformation instead of making the entire Earth move.

yor_on

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When I jump up does the Earth move down?
« Reply #3 on: 07/02/2009 17:36:06 »
When you're 'jumping' you just force the Earth to 'hunt you down':)
Treat her like the lady she is, and stop jumping on her...

chris

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• The Naked Scientist
When I jump up does the Earth move down?
« Reply #4 on: 07/02/2009 23:05:55 »
But LeeE - but this doesn't mean that the Earth doesn't all move, albeit by a miniscule amount, surely?

Chris

LeeE

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When I jump up does the Earth move down?
« Reply #5 on: 08/02/2009 01:00:00 »
But LeeE - but this doesn't mean that the Earth doesn't all move, albeit by a miniscule amount, surely?

Chris

Umm... could you re-phrase that please?

lightarrow

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When I jump up does the Earth move down?
« Reply #6 on: 08/02/2009 12:36:33 »
But LeeE - but this doesn't mean that the Earth doesn't all move, albeit by a miniscule amount, surely?

Chris
The Earth must move the same, because of momentum conservation law.

LeeE

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When I jump up does the Earth move down?
« Reply #7 on: 08/02/2009 12:43:53 »
The whole Earth doesn't need to move if just moving a small part of it will suffice.  If you want to look at it as a rigid-body problem though, then the Earth moves away from you when you jump up in the air but then starts moving towards you, just as you start moving towards it, as you come down again.  In this case, neither of you is stationary while you are in the air.

lightarrow

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When I jump up does the Earth move down?
« Reply #8 on: 08/02/2009 16:01:28 »
The whole Earth doesn't need to move if just moving a small part of it will suffice.  If you want to look at it as a rigid-body problem though, then the Earth moves away from you when you jump up in the air but then starts moving towards you, just as you start moving towards it, as you come down again.  In this case, neither of you is stationary while you are in the air.
With "whole Earth" you mean "All the Planet with all its parts" or just "a part of it"? Because if you really mean the first, then you can simply say that its centre of mass moves, because of momentum conservation law; if then the centre of mass moves because of...that part moves that way...and the other part in that way...ecc., it's not my problem!
Do you know what I mean? You have to identify a point of the entire system which represents the system's position in space, and the simpler one is centre of mass.
« Last Edit: 08/02/2009 16:05:47 by lightarrow »

Vern

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When I jump up does the Earth move down?
« Reply #9 on: 08/02/2009 16:08:18 »
Hi guys; I get the feeling we are trying to separate the excretory wastes of the house fly from spilled grains of pepper. It is a difficult task

yor_on

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When I jump up does the Earth move down?
« Reply #10 on: 10/02/2009 19:51:30 »
LeeE, although you are right in that it leads to a observable elastic deformation oscillating in a bit and then back, some rudiment of it I would expect to travel the whole way through the Earth and back.

Does that mean that we will have oscillations in more phases than one?
One from where we loose our observational ability and then those coming back from what we can't measure?
If this is correct.

LeeE

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When I jump up does the Earth move down?
« Reply #11 on: 11/02/2009 13:31:59 »

The deformation, as it propagated outwards, would soon be lost in the ambient noise caused by seismic, landslide, heating/contraction, road & rail traffic, wind, rain and insect activity.

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When I jump up does the Earth move down?
« Reply #11 on: 11/02/2009 13:31:59 »