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SaganRules
2010-Jan-25, 04:31 AM
Hello all, hope Xmas and New Year wasn't too much of a bore.:lol:
I was listening to an episode of Astronomy Cast a while ago and Dr Gay talked about as you approach the speed of light your mass increases and so you need much more energy to move.
Why is this? I also read that this is why the LHC needs such tremendous energy to push hydrogen particles along as they travel at close to the speed of light.
:confused:
I checked the FAQ for an answer but it is only for admin. (I'm new to the forum) Also you all seem to have such a grasp of physics and are very good at explaining very complicated concepts for non-scientists like me.

WayneFrancis
2010-Jan-25, 05:09 AM
It is because the energy used to speed you up is then stored in that object as kinetic energy. So the next time you try to speed the object up you not only have to speed up the object but all of the kinetic energy it also has.

At very slow speeds the kinetic energy isn't very large compared to the mass of the object so we don't notice a difference in the amount of energy it takes to speed up an object from 0 to say 5mph compared to 5mph to 10mph.

But as the speed starts approaching the speed of light the amount of kinetic energy can actually completely overwhelm the amount of mass the object has at rest.

So think of it this way. You rolling a snow ball across the snow. As you roll it it gets bigger (this represents the total energy of the system). The bigger it gets the harder it gets to roll it at the same speed because it has more total energy that you have to accelerate. Crude analogy but it might help you visualise what is happening a bit.

Jens
2010-Jan-25, 05:29 AM
So think of it this way. You rolling a snow ball across the snow. As you roll it it gets bigger (this represents the total energy of the system). The bigger it gets the harder it gets to roll it at the same speed because it has more total energy that you have to accelerate. Crude analogy but it might help you visualise what is happening a bit.

I think it's actually a difficult analogy, though your post in general was excellent. It's difficult because intuitively, we know that the extra mass is coming from the snow on the ground. I think the question the OP wanted to ask was, where does the extra mass come from in the case of matter? And I think the response, from the energy used to accelerate it, is the real key.

I'm not sure if this is a valid analogy, but wonder if it might be. If we conceive matter as a wave, which it is partly, then a wave being pushed forward by other waves will increase in height. I think that this is one way of visualizing what is happening.

WayneFrancis
2010-Jan-25, 05:38 AM
I think it's actually a difficult analogy, though your post in general was excellent. It's difficult because intuitively, we know that the extra mass is coming from the snow on the ground. I think the question the OP wanted to ask was, where does the extra mass come from in the case of matter? And I think the response, from the energy used to accelerate it, is the real key.

I'm not sure if this is a valid analogy, but wonder if it might be. If we conceive matter as a wave, which it is partly, then a wave being pushed forward by other waves will increase in height. I think that this is one way of visualizing what is happening.

That is why I said my analogy was crude. I like your analogy but again it might make people think that the object is actually getting bigger which it isn't. Such is the problems with analogies they inevitability break down if you try to take their meaning to far. The key is to be able to let go from the analogy when you've surpassed the concepts it is trying to relay.

Jeff Root
2010-Jan-27, 02:56 AM
Wayne,

I also think you made a particularly good start at an explanation, though a
rolling snowball probably shouldn't be part of it. Einstein did at first talk
about increasing mass of matter at high relative speed, but since then it
has been realized that the idea of changing mass is unnecessary and not
generally useful. Instead, just the increase in momentum and energy can
account for what is seen in a body moving at high speed relative to the
observer. The increase in momentum, for example, accounts for the
increasing difficulty in making particles in a particle accelerator go around
in circles, as well as the increasing difficulty in making them accelerate
any further.

-- Jeff, in Minneapolis