Can you explain the difference between relativistic mass and static mass?

Question

I asked a question awhile back and was told relativistic mass is not real mass. I had heard that it was impossible for matter to attain light speed because due to relativity, it would have infinite mass at that point. I had therefore assumed that the mass gained by an object was proportional to it's speed as it approached c, and that at 99% c regardless of its initial mass it's weight would be almost unfathomable. Tonight I noticed a response to a question, from a poster whose answers I trust, state that a 3.86 kg object traveling at 99% of the speed of light would weigh just 27.4 kg.


Am I confused about the relationship between weight and mass or relativistic mass and static mass or am I simply hopelessly lost.

Answer 1

In Newtonian mechanics,



F = ma



This is basically the definition of mass in Newtonian mechanics, it's the ratio between force applied to an object and resultant acceleration of the object.



In special relativity, the equation changes, becoming



F = γma



γ is the Lorentz factor. For slowly moving objects it's nearly 1, but for fast-moving objects it rises ever more sharply: 2.3 at 90% light speed, 7.1 at 99%, and 22 at 99.9%. For the protons accelerated in the LHC, γ is 7500.



"Relativistic mass" is γm. The term is used in teaching but many physicists reject it as not really meaningful.

Answer 2

Yes, I can. Relativistic mass is a whore's nightmare. It is an infinite number of different scalar values between a maxima (acceleration in the direction of motion) and a minima (acceleration exactly perpendicular to the line of motion). It arose from considering the energy formula for rest mass ( E = mc^2 ), and thinking that it would be cool to not have to learn the correct formula ( E^2 = (pc)^2 + (mc^2)^2 ). Rest mass is a constant, is so far identical to inertial mass, gravitational mass, and more.



"I asked a question awhile back and was told relativistic mass is not real mass."



Right, it is a f-ing mistake. No current textbook even tries to present the topic. Relativistic momentum you would expect to be different values as you move into "force space", since it is a vector. Mass should not change based on orientations.



"I had heard that it was impossible for matter to attain light speed because due to relativity, it would have infinite mass at that point."



Infinite energy, yes. Infinite mass, no. You will not form a black hole by someone seeing you move too fast.



"Am I confused about the relationship between weight and mass or relativistic mass and static mass or am I simply hopelessly lost."



Just start laughing and pointing when someone starts promulgating "relativistic mass", since they are pretty likely not to know how to use that b*tch the way it has to be used.

Answer 3

was told relativistic mass is not real mass.



I'm not sure what you mean by that. It's as real as your bank account.



What special relativity tells you is that the measurement of the same quantities, done from different frames of reference in motion relative to you, yields different values. But those are REAL values, they're not made up values. When you measure particles here on the surface of the Earth that result from the collision of cosmic rays with the atmosphere, those are REAL particles not "made up" particles. When the atomic clocks aboard GPS satellites is set up before deployment to be faster than clocks that remain at the surface, it is a real effect; the clock rate is as real here as it is from the satellites in orbit, it's just that different frames of reference measure differently.





assumed that the mass gained by an object was proportional to it's speed



It is certainly not proportional.



It looks proportional, and the velocity composition law looks linear, because the at small enough speeds the most important term of the Lorentz factor http://en.wikipedia.org/wiki/Lorentz_factor#Definition is a single linear term from the Maclaurin series for that factor. But the effect becomes noticeable (and quadratic, cubic and other terms of the series become dominant) at high enough velocities. But it is most certainly not proportional.





at 99% c regardless of its initial mass it's weight would be almost unfathomable.



Not quite. It'll be 1/sqrt(1-0.99^2) = 7.08881 i.e. around 7 times more massive than its rest mass; that's quite far from "unfanthomable", unless you consider an adult to be "unfanthomably" more massive than a child.



And by the way you mustn't confuse mass with weight. They're not the same thing.





a 3.86 kg object traveling at 99% of the speed of light would weigh just 27.4 kg.



See the above.





I confused about the relationship between weight and mass or relativistic mass



There is no relation. Mass is a measure of amount of matter, weight is a resulting force in the presence of a gravitational field. You feel weightless if you're freefalling, but you're NOT massless.

Answer 4

There is no distinction between relativistic mass and static mass. We call a body has a static mass if the body is at rest relative to you or the observer. It is a special case of relativistic mass. Mass of the body is known to change by the ,so called, Lorentz transformation for mass. The transformation formula is given by m=m'/√(1-v^2/c^2 ). Where m' is your static mass, m is the relativistic mass, and v is the speed of the body with respect to the observer and c is the speed of light. This equation is a product of the conservation momentum at relativistic speeds, i.e when the speed of the body is comparable to that of light.



This simple equation will explain what you just said above. This equation gives rise to the famous equation E = mc^2. Something interesting happens when you change the equation to

m=m'/√(v^2/c^2-1), you get an equation for Tachyons, they are superluminal or faster-than-light particles. Their speeds can never be lesser than c. They were first hypothesised by the scientist ECG Sudarshan, an Indian physicist. Such particles are known in Indian mythologies. If you want to know more just mail me and ask.

Answer 5

political science or social science relative to the total unknown number, static in numbers are known by listening & watching. General defense is relative and the patriot act static detection.

Answer 6

This book explains it:

http://www.amazon.com/Gravity-Driven-Universe-Roy-Masters/dp/1466200960

It is a unified field theory.

Einstein had a few things wrong, primarily that there is indeed a sort of "ether" and that gravity is a "push" not a "pull".

The reason (very simplified) mass can not achieve light speed is that as you accelerate, you are pushing against this sort of ether.



Ask yourself why light travels at light speed. You can slow it down by shining the light through glass, water, etc, but once it emerges, it speeds up to light speed again. How does it do that? Light has no engine, expends no energy accelerating. Obviously it is being both pushed and resisted by something. Ether, which is not static bu dynamic, lines of force going every which way pushes light but also resists it. You'll have to read the book.



Einstein said there are 2 kinds of gravity. Acceleration is one of them.