# Increase in mass & decrease in volume?

1. Jan 17, 2006

### young physical

hi everybody how are you?

this is the first time i write here , i hope i be good frind for you , & i'm sorry about my language , but i think i'm not very bad .

i have a quetion about the special theory of relativity?

Einstein sied" when the speed is increase the mass is increasing too. & the volume & tall is decrease".

if this right , so can any one explain to me how can i imagine the increasing of mass & decreasing of volume or tall? please.

i'm sorry agian. & good bye.

2. Jan 17, 2006

### HallsofIvy

Staff Emeritus
I'm not sure what you mean. An moving object, measured in your coordinate system, will have a smaller length (in the direction of motion) than if it were not moving in your coordinate system. Yes, as it speeds up (still as measured in your coordinate system) you will see it shrink. I'm not sure how one would "imagine" mass increasing- you can't see mass!
If you are concerned specifically about volume decreasing while mass increases, of course the density of the object is increasing.

3. Jan 17, 2006

### bernhard.rothenstein

mass, volume,density

mass and volume are two independent physical quantities. density is defined as a function of boss. detected from two different inertial reference frames density has different values. if you are interested how it goes have a look at
http://arxiv.org/abs/physics/0505190

4. Jan 18, 2006

### young physical

(I'm not sure what you mean. An moving object, measured in your coordinate system, will have a smaller length (in the direction of motion) than if it were not moving in your coordinate system. Yes, as it speeds up (still as measured in your coordinate system) you will see it shrink. I'm not sure how one would "imagine" mass increasing- you can't see mass!
If you are concerned specifically about volume decreasing while mass increases, of course the density of the object is increasing.)
hallow mr HallsofIvy, how are you? thanks for your explaining.

you siad"how one would "imagine" mass increasing". ok can we see the magnetic field ? No. is that right ?. but we can imagine it.

(the density of the object is increasing) that is what i want exactly>

thanks again.

5. Jan 18, 2006

### young physical

((mass and volume are two independent physical quantities. density is defined as a function of boss. detected from two different inertial reference frames density has different values. if you are interested how it goes have a look at
http://arxiv.org/abs/physics/0505190))

mr. bernhard.rothenstein welcome. nice to meet you. thank you for your reply.
thanks for a webside. i'll read it. but may be i back to asking you about it.:).
i'm sorry but what are you mean about boss? is it a mass?.
thanks againe.

6. Jan 18, 2006

### bernhard.rothenstein

mass volume density

read both. contact me for any question

7. Jan 19, 2006

### pmb_phy

Welcome!
I don't believe it was Einstein who said that but it is the length of an object which is parrallel to the direction of motion which contracts. Lengths perpendicular to the direction of motion remain unaltered.
You can imagine mass increase as due to changes in time and length since mass is defined in terms of momentum and momentum is defined in terms of velocity which is dependant on time and distance measurements.

For the details see my derivations here

http://www.geocities.com/physics_world/sr/light_clock.htm
http://www.geocities.com/physics_world/sr/lorentz_contraction.htm
http://www.geocities.com/physics_world/sr/lorentz_trans.htm
http://www.geocities.com/physics_world/sr/velocity_trans.htm
http://www.geocities.com/physics_world/sr/inertial_mass.htm

Nobody said a complete answer would be an easy one.

Pete

8. Jan 21, 2006

### Sheyr

We know that a massive object can not reach the speed of light because its mass would reach infinity and so the energy required to accelerate the body must be infinite, what isn't possible.... ??

First I understand that this is true for the observer at rest with respect to the moving body. But from the point of view of the moving observer its mass is not growing. The efect of mass increase is real but only for the observer at rest. Otherwise the moving observer would be able to detect the mass growth (for example by observing gravitational efects inside his reference frame) and so he would be able to determine his velocity, what is in contradiction to the special relativity.

So I can imagine that a moving observer having his own energy source (engine and fuel) can reach any velocity because from his point of view his mass doesn't change. Furthermore, the observer at rest, that notices the growth of mass of the moving body notices also the growth of mass of the fuel and so the energy of the fuel grows, since $$E = m c^2$$.
At the velocity that equals the speed of light both the mass of the moving observer and the energy of his fuel will equal the infinity.

9. Jan 21, 2006

### bernhard.rothenstein

Every thing in special relativity is a direct conseqence of the fact that light (signals) propagate with finite and invariant speed and opf the fact that Nature prevent us from finding out that we are at rest or in a state of uniform motion!

10. Jan 22, 2006

### young physical

mr.bernhard.rothenstein
mr. pmb_phy
mr.Sheyr
thank you very mush my frinds that very useful.
but i'm sorry i can't discussing your replies because i have examination, but i promise you i'll back in the end of next week & i'll continue the discussion.

i'm very sorry.

young physical