- #1

Anttech

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As nothing can go faster than the speed of light the object must have a terminal velocity also due to E=mc^2, and A=F/M...

I am just wondering if you can calculate the terminal velocity from the objects static mass.

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- Thread starter Anttech
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- #1

Anttech

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As nothing can go faster than the speed of light the object must have a terminal velocity also due to E=mc^2, and A=F/M...

I am just wondering if you can calculate the terminal velocity from the objects static mass.

- #2

Anttech

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sorry I should have added, with a constant force acting on the object, like g on earth...

- #3

NateTG

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In Newtonian mechanics, the object goes faster and faster forever.

In Special Relativity, if the force is constant, the mass that the object gains through kinetic energy will decrease the acceleration preventing it from ever getting to c.

In General Relativity (which I'm not familiar with) it might be possible to demonstrate that a constant acceleration (not constant force) path like that leads into a black hole.

For more information, you should look into information on particle accelerators.

- #4

Anttech

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Here is the scenario I have conjered up:

An object of know mass, has a solar powered engine of knowen mass attached to it and has a thrust of know quantity applied to the system when knowing the total mass of the system could you calculate the terminal velocity in a vacuum...

:)

- #5

HallsofIvy

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The objects velocity approaches c as a limit.

If you wanted to calculate the velocity as a function of time, you would have to specify the force as a function of time.

- #6

Anttech

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Force as a function of time, is this not power... or am I missing the point...

- #7

Anttech

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Originally posted by HallsofIvy

The objects velocity approaches c as a limit.

If you wanted to calculate the velocity as a function of time, you would have to specify the force as a function of time.

Sorry I am not with you 100%... How can the velocity approach C if the mass increase as the KE increases, surely there must be a point where the mass approaches infinite and therefore the acceleration becomes 0 if you are applying a constant force (a=f/m)...

can you explain what you said with a little more depth?

thx

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- #8

russ_watters

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Yes, I think you missed the point - Hurkyl gave you the answer: C.Originally posted by Anttech

Force as a function of time, is this not power... or am I missing the point...

And power is force times distance times time.

- #9

jcsd

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From your point of view you would just keep on accelrating under this force, as after all it is a constant force, but if we take an observer who was in your rest frame when the force was applied he would view your velocity appraoching c as time approaches infinity.

- #10

Anttech

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Forgive me if I am coming over as stupid :)

- #11

krab

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Originally posted by russ_watters

Yes, I think you missed the point - Hurkyl gave you the answer: C.

And power is force times distance times time.

Russ: Power is force times distance over time, or Force times velocity.

- #12

jcsd

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Originally posted by Anttech

Forgive me if I am coming over as stupid :)

I just used k as a generic constant, i.e. the force is always constant and always equal to some fixed value k

- #13

Anttech

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"How would you "weight" a plane without scales?" If you can think of any other way you could do this I would be much obliged...

thx

- #14

sigSEGV

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- #15

NateTG

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Originally posted by Anttech

"How would you "weight" a plane without scales?" If you can think of any other way you could do this I would be much obliged...

How about mass spectrometry?

- #16

russ_watters

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Oops. I do that sometimes.Originally posted by krab

Russ: Power is force times distance over time, or Force times velocity.

- #17

Anttech

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Originally posted by NateTG

How about mass spectrometry?

Good idea! :)

- #18

Haelfix

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Eg count all the constituent particles, go ot the rest frame, add up the energies presto mass.

You can do it with gravity too, for instance, measure the curvature of space that the plane induces on the metric. Eg, measure light deviation the plane causes.

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