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### Author Topic: How does mass increase at higher speeds?  (Read 44418 times)

#### cheryl j

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##### How does mass increase at higher speeds?
« on: 27/11/2012 18:32:17 »
I'm sorry if this is a dumb question but physics is not really my area. I've been listening to the CBC Massey lectures by physicist Neil Turok, which I quite like. Anyway, when he talks about mass increasing at higher speeds, how does that happen? Is there actually an increase in the amount of matter or atoms or particles? Or does it just take more force to accelerate it? I had always thought that mass and matter were the same thing.
« Last Edit: 04/12/2012 22:32:33 by chris »

#### simplified

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##### Re: How does mass increase
« Reply #1 on: 28/11/2012 09:36:38 »
I'm sorry if this is a dumb question but physics is not really my area. I've been listening to the CBC Massey lectures by physicist Neil Turok, which I quite like. Anyway, when he talks about mass increasing at higher speeds, how does that happen? Is there actually an increase in the amount of matter or atoms or particles? Or does it just take more force to accelerate it? I had always thought that mass and matter were the same thing.
If you stop photon then mass increases.

#### Soul Surfer

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##### Re: How does mass increase
« Reply #2 on: 28/11/2012 11:00:51 »
when you try to accelerate a particle or a larger object towards the velocity of light.  As you get close to this velocity it gets much harder to accelerate as if its mass had increased so that however hard you try you cannot actually increase the velocity of light but you are increasing its kinetic energy.  The famous equations of Einstein tell you how this increase works.

The reason for this is that Einstein realised that the laws of physics cannot change when you are moving, because you can only find out if you are moving  (or something else is moving )  by looking at something else.  Also if you only have one other thing to look at to tell you that you are moving you cannot tell which of you (or both of you ) are moving.

This results in the fact that light must travel at the same speed to you whatever speed you are doing because a famous experiment done 125 years ago "The Michelson Morley experiment" was designed to measure the true velocity of the earth through space by measuring the velocity of light in different directions throughout the year failed to measure the change brought about by the velocity of the earth in its orbit round the sun.  This should have easily been detectable and came as a total shock to physicists at the time.

The non variability of the velocity of light with motion had has been proved experimentally to be true to one part in 10**-17 in recent years
« Last Edit: 28/11/2012 11:07:14 by Soul Surfer »

#### yor_on

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##### Re: How does mass increase
« Reply #3 on: 28/11/2012 17:43:54 »
Relativity is always about about two 'frames of reference', measuring one relative the other. So when we say that somethings mass has increased due to a velocity, or speed, we always define it relative some other object, the observer. The fact is, as far as I can see that is :), that all uniform motions is the same, no matter what 'speed' they will seem to have relative you. So the 'mass' you find should then be a representation of the energy a collision (between you and what you measure against) would produce, and also about directions.

Locally, as long as you're uniformly moving, it shouldn't change anything in your local experiments, although you might find starlight outside your solar system to blue shift. Accelerations are another thing in that they are locally (intrinsically?) measurable whereas a uniform motion always will need a referent to measure a speed.

#### Pmb

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##### Re: How does mass increase
« Reply #4 on: 02/12/2012 15:27:42 »
I'm sorry if this is a dumb question ...
Don't worry. It's not a dumb question, so your safe. :)

Note: relativistic mass is often also referred to by the name inertial mass.

Anyway, when he talks about mass increasing at higher speeds, how does that happen? Is there actually an increase in the amount of matter or atoms or particles? Or does it just take more force to accelerate it? I had always thought that mass and matter were the same thing.
[/quote]
Yes. It does require an increased force by an amount which is greater than the
Newtonian expression.

For a list of jouirnal articles on this subject please see
http://home.comcast.net/~peter.m.brown/ref/mass_articles/mass_articles.htm

Meanwhile I can give you the gist of it. The increase in mass is a result of the properties of spacetime. The combination of the relationship between space and time between two different inertial frames, one the rest frame of the observer. m and the other the rest frame of the particle M, shows that M = m/sqrt(1 - v^2/c^2).

The derivation can be found at my website which is at
http://home.comcast.net/~peter.m.brown/sr/inertial_mass.htm

If you're really randy about this subject I studied this aspect of relativity in great deal and summarized it in this (unpublished) paper. Why would you consider reading an unpublished paper? For the same reason you'd consider reading a post I'd post in a thread. With that in mind the article is at http://arxiv.org/abs/0709.0687

#### Phractality

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##### Re: How does mass increase
« Reply #5 on: 02/12/2012 20:08:39 »
I'm gradually seeing the fallacy in my reasoning about planetary orbital periods. If you have a continuous ring of tiny planets in a circular orbit about their barycenter, and you observe that from a frame moving at .866 c relative to the barycenter, the ring of orbiting planets will appear elliptical. It will be half as wide in the direction of relative velocity. However, the individual planets are not moving in an ellipse in that reference frame. Instead, they are following a cardoid path. To determine their acceleration in that reference frame, you have to analyze the cardoid motion, and that probably requires GR.

#### a_dark_knight

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##### Re: How does mass increase at higher speeds?
« Reply #6 on: 05/12/2012 06:14:51 »
I vote that it's actually inertia which increases, not mass. To say mass is incredibly misleading, in my opinion. And the inertia doesn't *really* increase, it's just that there's kind of a gap between two perspectives moving very fast relative to eachother. They disagree about time flow which results in these weird effects, like objects seeming heavier and harder to push than usual. It's because in a sense they're moving faster than they appear, so the rest of that momentum goes into this apparant "weight".

#### Pmb

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##### Re: How does mass increase at higher speeds?
« Reply #7 on: 05/12/2012 06:22:23 »
I vote that it's actually inertia which increases, not mass.
These are not independant things. Mass is the measure of something's inertia.

#### lightarrow

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##### Re: How does mass increase at higher speeds?
« Reply #8 on: 07/12/2012 18:36:29 »
How does mass increase at higher speeds?
It doesn't.

#### Bill S

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##### Re: How does mass increase at higher speeds?
« Reply #9 on: 08/12/2012 17:05:45 »
Hi Cheryl J; having worked through this thread I find myself wondering if your original question was answered.  I think it may have been, but that could be because I had my own pre-conceived idea as to what it should be.

I would be fascinated to know your thoughts.

#### JP

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##### Re: How does mass increase at higher speeds?
« Reply #10 on: 08/12/2012 17:25:19 »
I vote that it's actually inertia which increases, not mass.
These are not independant things. Mass is the measure of something's inertia.

How does mass increase at higher speeds?
It doesn't.

Both are right.  Like many things in modern physics, we've realized that when we go to extremes that are way outside of our daily experience, seemingly simple concepts like mass can have multiple definitions.

In paticular, at high speeds two types of mass can be defined: invariant mass and relativistic (or inertial) mass.  At slow speeds, both are equal and reduce to our everyday idea of mass.

When someone says mass increases at high speeds, they're talking about relativistic mass.  Both Soul Surfer and pmb gave good explanations of why relativistic mass increases: it gets more energy to boost something's speed by the same amount if it's going fast than if it's going slow.

When someone says mass doesn't change at high speeds, they're talking about invariant mass, which by definition stays the same at all speeds.  Both have their uses in physics, and so long as you're clear about which one you're using, you won't have problems.  You can get to one from the other.  However, most physics courses and physicists mean invariant mass when they say mass, since that's become the standard concept taught in class.

#### lightarrow

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##### Re: How does mass increase at higher speeds?
« Reply #11 on: 08/12/2012 20:29:37 »
Does a human being become a massive black hole, if moving fast enough? Then we all should be, since we all are moving fast enough, with respect to some very fast particle or with respect a far galaxy receding from us at relativistic speed.

#### JP

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##### Re: How does mass increase at higher speeds?
« Reply #12 on: 08/12/2012 21:46:15 »
That would make sense if there was a unique definition of mass that was defined in terms of the formation of black holes, but it's not...

I actually tend to agree with you, lightarrow, that invariant mass is the better definition to use for many things, including when teaching students relativity.  It's certainly the only definition I found useful in a bit of work I did in graduate school.  I don't oppose experts in the field using relativistic mass if they tell me it's useful for them.  I don't know enough cosmology to intelligently criticize or support its use there, for example.
« Last Edit: 08/12/2012 21:53:52 by JP »

#### a_dark_knight

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##### Re: How does mass increase at higher speeds?
« Reply #13 on: 11/12/2012 10:09:21 »
These are not independant things. Mass is the measure of something's inertia.

But mass creates a gravitational field. Whereas inertia doesn't, in my opinion. That's the distinction I'm referring to. Mass also implies the amount of "stuff" (or matter) whereas inertia is just resistance to a force. So does that mean that things moving near the speed of light have a larger gravitational field than they would otherwise? Maybe it would normally be negligible but the whole point of science is to be accurate.

#### yor_on

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##### Re: How does mass increase at higher speeds?
« Reply #14 on: 11/12/2012 15:51:22 »
That's a really good point Dark :)
Relativistic mass and 'gravity' are not the same.
But if we use 'energy' as our measure then?
=

Although, you have uniform constant accelerations to consider too?
But if we're talking 'speeds' as something uniformly moving.
« Last Edit: 11/12/2012 15:53:21 by yor_on »

#### JP

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##### Re: How does mass increase at higher speeds?
« Reply #15 on: 11/12/2012 16:17:06 »
That's a really good point Dark :)
Relativistic mass and 'gravity' are not the same.
But if we use 'energy' as our measure then?

You have to use the stress-energy tensor: http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor
This is a reason why arguments that only involve mass break down, e.g. why don't moving masses become black holes since they get heavier?

A simpler argument is that it's really the invariant mass that matters if it's possible to catch a ride on the mass.  Then you'd see the mass at rest with respect to you and its field would be entirely due to its invariant mass.  You could then figure out its gravitational field in any reference frame you chose by using GR to change reference frames.

#### yor_on

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##### Re: How does mass increase at higher speeds?
« Reply #16 on: 11/12/2012 19:41:11 »
Let's take a example that gives us a totally new, and well earned, headache :)

Consider yourself heating up a gram of some, very, temperature resistant metal. You've weighted it before but after it gets heated you weight it again, finding it to weight more. One way to describe it might be to consider the particles making the material accelerating inside the metal as they gain 'energy' from heat, moving agitatedly. Can we then discuss those particles as gaining a relativistic mass, or not?

If they have we also find that this relativistic mass indeed have changed the 'proper' mass, that is if we would confine a proper mass to be whatever constitutes of that piece metal macroscopically..

And is it 'accelerations' that do it, or 'uniform motion' :)

#### JP

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##### Re: How does mass increase at higher speeds?
« Reply #17 on: 11/12/2012 23:12:49 »
Yor_on, here's the same question, but in a slightly more extreme form:  If you have a box made of perfect mirrors and you inject some light into it, the box's energy has now increased.  If it's sitting still next to you, its mass increases (by E=mc2, which holds for stationary objects).  So clearly its mass, measured at rest, went up.  Since invariant mass is supposed to not change with reference frame, and the rest frame is a reference frame, its invariant mass also went up.  Additionally, if you try to push it, you'll find its inertial mass went up.

But photons individually have no mass?  How did it gain mass?

#### cheryl j

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##### Re: How does mass increase at higher speeds?
« Reply #18 on: 12/12/2012 02:47:36 »
Hi Cheryl J; having worked through this thread I find myself wondering if your original question was answered.  I think it may have been, but that could be because I had my own pre-conceived idea as to what it should be.

I would be fascinated to know your thoughts.

I think I'm more confused than ever.

#### cheryl j

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##### Re: How does mass increase at higher speeds?
« Reply #19 on: 12/12/2012 03:02:15 »
okay, what about that weird meter stick thought experiment where different observers pass it going different relative speeds. Does the meter stick really become shorter as the observers approach the speed of light. Is there "less" of the meter stick? Because in this experiment it doesn't sound like the meter stick's mass, matter, or inertia has changed at all, the observers are different.

#### JP

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##### Re: How does mass increase at higher speeds?
« Reply #20 on: 12/12/2012 03:14:16 »
Hi Cheryl J; having worked through this thread I find myself wondering if your original question was answered.  I think it may have been, but that could be because I had my own pre-conceived idea as to what it should be.

I would be fascinated to know your thoughts.

I think I'm more confused than ever.

At the risk of confusing matters more...

If you understand mass as a measure of the "resistance" of something to being pushed faster, then it does increase as the speed increases.  In brief, since the speed of light is a limit, it takes more and more work to push something and speed it up as you get closer to the speed of light.  The number of particles stays the same, so the amount of matter doesn't increase in that sense.

Any time this gets brought up, it'll start an argument over the correct definition of mass.  The problem is there are other definitions which don't agree with the above.  For slowly moving things all definitions DO agree, but at high speeds they differ.  The standard, textbook definition that's taught these days does not increase as speed increases, but I'll leave that to others to debate.

#### JP

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##### Re: How does mass increase at higher speeds?
« Reply #21 on: 12/12/2012 03:15:14 »
okay, what about that weird meter stick thought experiment where different observers pass it going different relative speeds. Does the meter stick really become shorter as the observers approach the speed of light. Is there "less" of the meter stick? Because in this experiment it doesn't sound like the meter stick's mass, matter, or inertia has changed at all, the observers are different.

No more matter is created or destroyed in the meter stick.  The number of particles in it stays the same.  The shape of the particles will change as they'll now be measured to be short.

#### lightarrow

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##### Re: How does mass increase at higher speeds?
« Reply #22 on: 12/12/2012 15:15:54 »
Let's take a example that gives us a totally new, and well earned, headache :)
Not to me
Quote

Consider yourself heating up a gram of some, very, temperature resistant metal. You've weighted it before but after it gets heated you weight it again, finding it to weight more.
Correct.
Quote
One way to describe it might be to consider the particles making the material accelerating inside the metal as they gain 'energy' from heat, moving agitatedly.
Correct.
Quote
Can we then discuss those particles as gaining a relativistic mass, or not?
You can discuss it, but there is no need of relativistic mass to describe that fact.
In physics is Very important to give attention to which is the physical system considered. The system of particles inside the gram of metal *it's not* the simple "sum" of the particles. Do you remember when I showed that a system of 2 photons with opposite velocities has non zero invariant mass?

There is a way of saying that "the whole is more than the sum of its parts". Something similar in physics (or, at least, in this case).

#### yor_on

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##### Re: How does mass increase at higher speeds?
« Reply #23 on: 12/12/2012 22:47:03 »
Heh :)

I can see you and Pete gearing up to a argument Lightarrow :)
But I think you can use the idea to argue a 'relativistic mass', if you want?
You can translate the particles agitations into accelerations, and a added '(mass)energy' confined inside the metal.

It depends on how you define 'gravity' though. Using the original equivalence it must be a constant uniform acceleration, but to me all accelerations should present you with a inertia/gravity. The squid those guys used to create a dynamical Casimir effect should have weighted a 'little' more if I'm thinking right there.
« Last Edit: 12/12/2012 22:49:36 by yor_on »

#### Bill S

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##### Re: How does mass increase at higher speeds?
« Reply #24 on: 12/12/2012 23:33:52 »
[quote = Cheryl J]okay, what about that weird meter stick thought experiment where different observers pass it going different relative speeds. Does the meter stick really become shorter as the observers approach the speed of light. Is there "less" of the meter stick? Because in this experiment it doesn't sound like the meter stick's mass, matter, or inertia has changed at all, the observers are different.[/quote]

I think it all depends on the frame of reference.  In trying to get my head round this I resorted to a thought experiment that can easily be turned into a real one.  All you need is a blank wall, a directional light and a metre (OK, the spell checker doesn't like UK spelling, but I'm too old to change  :P ) stick.  Hold the stick parallel to the wall and stick and shadow are the same length.  Rotate the stick and the shadow becomes shorter.

In its own F of R, the stick is the same length, but in the F of R of the wall (or the observer) it is measurably shorter.

The scientists on the forum will probably throw up their hands in horror, but it helped me.

#### The Naked Scientists Forum

##### Re: How does mass increase at higher speeds?
« Reply #24 on: 12/12/2012 23:33:52 »