Mass Dilation: Does 0.9c Travel Increase Mass?

[aonin]

Hey guys, i was just wondering what would happen if a person was on a spacecraft traveling at 0.9c was standing on a set of scales that measured his mass, went past a stationary observer.

Would the stationary observer see the reading on the scales increase due to mass dilation?

I asked a few people in our physics class, they kinda said that since the total mass of the spacecraft increases in the reference frame of the stationary observer, for example the springs and stuff in the scales would have more mass and and be harder to push down therefore the reading will not increase?

will there be a contradiction?

could you hopefully explain this in high-school level terms, all we've learned are the mass dilation equations lol

thanks

 

[Bill_K]

In the early days of relativity, even before Einstein came along, people came up with several concepts to help them understand what happens to objects moving at large velocities. These include time dilation, Lorentz contraction and what you refer to as 'mass dilation', or relativistic mass. Fortunately we now understand relativity much better and can do away with these outdated concepts. While the effects associated with them are real, the idea that meter sticks *really* contract, or massive objects *really* get heavier often lead to confusion like you're having.

Relativistic mass is just a way of expressing the fact that it becomes harder and harder to accelerate an object that is moving at high speed. It does not mean you really weigh more. If a person weighs himself by standing on a scale, the reading on the scale is the same in any rest frame.

 

[noone123]

Hey Bill K. Isn't the mass increase seen from an another reference point will only be apparent? The person inside the spacecraft will not notice any mass change.
im so confused lol

 

[jtbell]

Would the stationary observer see the reading on the scales increase due to mass dilation?

No, all observers would see the same reading on the scale. If it has a digital readout that shows 100 kg to the person on the spaceship, everybody else would see it, too. (leaving aside technical issues with being able to read a device that's whizzing past you at 0.9c )

 

[ghwellsjr]

Only problem is that on a spacecraft traveling at any constant speed, everybody is weightless and won't even be able to stand let alone stand on a set of scales to weigh themselves. However, there are ways to measure mass (using acceleration) and if there were such an instrument with some kind of readout, everyone on the moving spacecraft and the stationary observer would all see the same numbers on the readout.

I think what you are really asking about is whether the mass of the spacecraft has increased as viewed by the stationary observer. So if a rocket fires on the spacecraft to accelerate it to a faster speed, it will not have the same affect as viewed by the stationary observer as it had when the spacecraft was first starting out. The speed change will be much lower.

 

[aonin]

well just assuming the spacecraft is traveling very close to the surface of the eart at 0.9c, would there be change in the reading on the scales of the weight of the person in the spacecraft as seen by the stationary observer? obviously the person in the spacecraft would not experience mass dilation in his own frame of reference.

 

[nsh3a94]

Wouldn't the non existence or "outdatedness" of mass dilation refute the mass-energy equivalence?