Relativistic momentum

[suyash]

What happens when relativistic momentum becomes infinite?

or what happens when the speed of an object approaches c?

One last question, Why is it not possible to travel at and more than speed of light?

 

Feel free to use formulas to support your answers!

[Country Boy]

"Relative momentum" can't "become infinite". It can become "arbitrarily large" as its speed increases relative to you. There are many reasons why speed cannot be greater than the speed of light. It looks like the one you are thinking of is that since the momentum becomes arbitrarily large, so does the force necessary to increase its speed. As the speed gets closer to c, the force necessary to increase the speed "goes to infinity in the limit as speed approaches c" (not the same as "becomes infinity").

[Sriman Dutta]

For relativity, we have relativistic mass [math]m[/math] as-
[latex]m=\frac{m_0}{\sqrt{1-\frac {v^2}{c^2}}}[/latex]
So as v tends to be c, m becomes infinite. So an infinite amount of energy is required to make the object move at c.

 

 

Moderator: fixed your latex

[Raider5678]

What happens when relativistic momentum becomes infinite?

or what happens when the speed of an object approaches c?

One last question, Why is it not possible to travel at and more than speed of light?

 

Feel free to use formulas to support your answers!

For your last two questions, I actually have an answer. Thanks to science forums(Thanks guys. I think.)

When an object approaches the speed of light, time starts to move slower.(https://en.wikipedia.org/wiki/Time_dilation#Relative_velocity_time_dilation) It's more complicated then that to explain why time moves slower, but that's basically it. Now it's important to note that time isn't speeding up for the outside world. It's simply moving slower for the object moving at that high of a speed. This is involved in the theory of relativity, which makes for a good read if you have a few days to really study it.

Now pertaining to your last question.

First, nothing can move faster then light because lights already the fasting thing out there. You can't make anything faster, so there's nothing that could be used to push you faster then light.

But that's an edgy answer. A better answer would be that since speed is distance/time, it's referring to how much time passes for you. Not the area around you. This is because while moving that fast would make it seem like time around you went faster, it didn't. Your time went slower. So you actually traveled slower compared to if there was no time dilation. Basically, by the time you reach the speed of light, time will move so slowly for you that you won't be traveling at the speed of light.

[mistermack]

The picture I have, is that when an object gets close to c, it's particles become more and more LIKE light. And to reach c, they would have to become light.

Light travels in a straight line. The energy in particles is in motion in all sorts of directions.

As the particle travels faster and faster, more and more of it's internal motion becomes straight-line in the direction that it's moving.

To travel at c, all of it's motion would have to be in the straight line direction of travel, and it would then be light.

But nothing exists that can push it to that speed, as anything that has mass is going slower than c.

[Sriman Dutta]

If an object with mass gets closer to speed of light, it doesn't become like the particles of light. If this were to happen, then the above equation would not hold true, which shows that as velocity approaches c, mass becomes infinitely large and does not become mass less as photons.

[Klaynos]

The picture I have, is that when an object gets close to c, it's particles become more and more LIKE light. And to reach c, they would have to become light.

Light travels in a straight line. The energy in particles is in motion in all sorts of directions.

As the particle travels faster and faster, more and more of it's internal motion becomes straight-line in the direction that it's moving.

To travel at c, all of it's motion would have to be in the straight line direction of travel, and it would then be light.

But nothing exists that can push it to that speed, as anything that has mass is going slower than c.

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[kjelleman]

To understand this phenomenon one cannot utilize concepts as mass and time since that results in circular reason. What we mean by mass and time is how much an object is influenced by a given force. A slower response to a force we conceive as larger mass and/or slower time. So what happens at speed of light? At this speed there is no interaction since the mediator of force is itself travelling at the speed of light. If the object move at speed of light the mediator cannot be received. This we experience as infinite mass/momentum and/or time standing still.

Please see chapter 9 of my text book for a more thorough discussion:

 

link deleted - rule 2.7

[mistermack]

If an object with mass gets closer to speed of light, it doesn't become like the particles of light. If this were to happen, then the above equation would not hold true, which shows that as velocity approaches c, mass becomes infinitely large and does not become mass less as photons.

If an object emits a photon, it loses mass. So that part of it's mass has become light.

I agree that an object can't become like light by moving at c.

But neither can it be accelerated to c, and infinite mass.

Both are impossible cases.

 

For something with mass to move at c, something impossible has to happen. That was how I was trying to put it.

[Bird11dog]

Why is it we always look at an object near c and never out from an object near c?

[Strange]

Why is it we always look at an object near c and never out from an object near c?

 

 

As velocity is relative, this is exactly the same thing. If you are stationary and observe an electron (for example) moving at near c, that is exactly the same as you moving at near c and observing a stationary electron.

[imatfaal]

Why is it we always look at an object near c and never out from an object near c?

 

Firstly, the observer always views himself as stationary - there is no dilation nor contraction in the rest frame.

 

And secondly, it all works out the same; this is one of the basis of relativity that there are no privileged frames. Something flying past the solar system which we measure as .9c will see the solar system moving past them at .9c. And all the physics still works out.

For an example of something worked from both frames you can look up atmosphereic muon decay

http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/muon.html

[mistermack]

If an object with mass gets closer to speed of light, it doesn't become like the particles of light. If this were to happen, then the above equation would not hold true, which shows that as velocity approaches c, mass becomes infinitely large and does not become mass less as photons.

Reading a little more, it's an interesting concept.

What approaches infinite largeness, is the relativistic mass. The rest mass doesn't alter one way or the other.

The relativistic mass is an expression of the momentum and energy of an object in motion.

It's different in every inertial frame. So if your chosen inertial frame is close to the speed of light, relative to an electron, then the electron will have approaching infinite relativistic mass.

 

Einstein didn't like the concept of relativistic mass. As late as 1948 he wrote that it was better to use the expressions for momentum and energy than use relativistic mass.

[swansont]

 

Please see chapter 9 of my text book for a more thorough discussion:

 

link deleted - rule 2.7

 

 

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