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Author Topic: How do moving objects slow down in space?  (Read 6626 times)

ThreeWords

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How do moving objects slow down in space?
« on: 21/10/2009 17:33:14 »
Forgive me if this is an over simple question, but is there anything that will slow down a moving object in space. This is assuming that there is nothing nearby, like objects with powerful gravity or magnetic force.
Does there exist anything that will cause it to slow?

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« Last Edit: 24/10/2009 20:13:02 by chris »

lightarrow

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Re: How do moving objects slow down in space?
« Reply #1 on: 21/10/2009 19:16:37 »
Forgive me if this is an over simple question, but is there anything that will slow down a moving object in space. This is assuming that there is nothing nearby, like objects with powerful gravity or magnetic force.
Does there exist anything that will cause it to slow?
A particle's beam is in the class of 'objects with powerful gravity or magnetic force'? Even light can slow down a moving object.
« Last Edit: 22/10/2009 14:34:07 by lightarrow »

LeeE

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Re: How do moving objects slow down in space?
« Reply #2 on: 21/10/2009 22:09:15 »
Regarding an isolated object in outer-space, I think we can assume that the light and particles falling upon it from all sides will be balanced, so in Newtonian physics, nothing should slow it.  However, in Relativity, linear frame-dragging will tend to slow it down.

lightarrow

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Re: How do moving objects slow down in space?
« Reply #3 on: 22/10/2009 14:31:42 »
Regarding an isolated object in outer-space, I think we can assume that the light and particles falling upon it from all sides will be balanced, so in Newtonian physics, nothing should slow it.  However, in Relativity, linear frame-dragging will tend to slow it down.
This is almost exactly true. Not exactly because, let's say CMBR radiation for example, has an higher frequency and an higher intensity (not because of the higher frequency, but for a different, even if related, reason) in the front side than in the back side of the object. It is quite intuitive, thinking in terms of particles (in this case photons): you will find an higher density of impinging particles per unit time in front of you, than those reaching you from the back.
« Last Edit: 22/10/2009 14:33:44 by lightarrow »

yor_on

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Re: How do moving objects slow down in space?
« Reply #4 on: 22/10/2009 20:47:50 »
Difficult question that one. To state it as you do you will have to make some assumptions first. For example that this 'object' exist solely on its own having no fields or 'forces' acting on it from anywhere. To do that you need to step outside SpaceTime as both electromagnetic waves and light, as well as gravity, is expected to exist at all distances as I understands it?

LeeE

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Re: How do moving objects slow down in space?
« Reply #5 on: 22/10/2009 23:06:56 »
Good point lightarrow, assuming that the traveling object has been accelerated to its relativistic velocity from an inertial frame of reference where the CMBR was uniform.

Soul Surfer

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Re: How do moving objects slow down in space?
« Reply #6 on: 23/10/2009 23:13:20 »
The simpple answer to this question is no.  All the slowing down effects are veery small indeed and things essentially continue to move for ever

lightarrow

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Re: How do moving objects slow down in space?
« Reply #7 on: 24/10/2009 15:27:36 »
Good point lightarrow, assuming that the traveling object has been accelerated to its relativistic velocity from an inertial frame of reference where the CMBR was uniform.
Exactly. Our group of galaxies for example is moving at ~ 630 km/s with respect it.

litespeed

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How do moving objects slow down in space?
« Reply #8 on: 01/11/2009 19:15:45 »
Any object in space is subject to multiple forces. If the object you are talking about is near a black hole, it will not slow down, it will accelerate. Similarly, the given object will at all times be subject to unequal gravitational forces as it progresses. These could alternate from acceleration to deaceleration.

Finally, space is not empty. Even if all gravitational forces in all directions remain constant, which it will not, the object will encounter all sorts of other objects such as hydrogen, and all the other byproducts of solar fusion. If they hit it from the back it will accelerate etc.  Finally, apparently light itself seems to have 'momentum' and will produce and equal and oposite force of acceleration as it is relfected.

This is something I am entirely accepting on faith.  If light has no mass, how can it impart momentum by simple reflection. Perhaps the wave length of the light is reduced and the diference is converted to momentum of the object [which would be calculated by the increase mass the object would also accumulate as a result of acceleration]. Specifically, light can transmit energy in the form of increased mass and acceleration of that mass.

JP

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How do moving objects slow down in space?
« Reply #9 on: 01/11/2009 19:30:44 »
This is something I am entirely accepting on faith.  If light has no mass, how can it impart momentum by simple reflection. Perhaps the wave length of the light is reduced and the diference is converted to momentum of the object [which would be calculated by the increase mass the object would also accumulate as a result of acceleration]. Specifically, light can transmit energy in the form of increased mass and acceleration of that mass.

In general relativity, (invariant) mass is given by E2/c2-p2=m2c2,
where E is energy, c is the speed of light, and m is mass.  Since light has energy, but zero mass, then it has to have momentum, so that E2/c2-p2=0.  Since momentum is a vector, a change in direction means a change in momentum, so as you say, direction changes from reflection are the usual way it imparts momentum, or absorption.
« Last Edit: 01/11/2009 19:32:17 by jpetruccelli »

yor_on

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How do moving objects slow down in space?
« Reply #10 on: 25/12/2009 22:57:09 »
Nice explanation

Geezer

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How do moving objects slow down in space?
« Reply #11 on: 26/12/2009 00:04:41 »
Ultimately I think it will give up kinetic energy to heat. Gravitational effects distort objects to produce heat, and collisions with the small amount of matter in deep space create friction. In deep space, these effects are extremely small, but they exist nonetheless. More importantly, they are not reversible, so over time the body will lose kinetic energy.

 

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