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[Evad]

Originally posted by BeefontheBone@Jun 22 2005, 04:13 AM
How do you mean? A formula for what?

your previous post beef, sorry i wasn't clear

[BeefontheBone]

Ok, suppose we have an observer O, and a spaceship is travelling at half the speed of light relative to O. If the spaceship is 10m long when at rest, how long does it appear to be to the observer?

The Lorentz factor gamma is equal to 1/sqrt(1-(v/c)^2), so in this instance where v/c=1/2, gamma=1/sqrt(3/4)=2/sqrt3 which is roughly 1.15. The ship will appear to have length 10m/1.15 = 8.66m

My A-level physics teacher used to set problems like the following: Suppose I can run at any speed up to the speed of light, and I need to get my 10m-long ladder through my garage, which is unfortunately only 7.5m long, and has a door in 2 facing walls. There's a problem with my doors however, so only one can be open at a time (and they open and close instantaneously for the sake of argument) - how fast do I need to run in order to get the ladder through the garage?

The classic example of the time dilation is the so-called Twins Paradox. Suppose 2 identical twins are on Earth, and one (Alan) heads into space on a spaceship which travels at a significant fration of the speed of light on a ten-year mission before returning to Earth, while Brian remains at home. From Brian's point of view Alan is travelling, so time slows down for him - Brian sees Alan ageing less than the 20 years Brian has aged. On the other hand, from Alan's perspective Brian is moving away from him at speed, so on Alan's return he thinks Brian is younger.

The paradox isn't really a paradox - the relative motion is not constant (the ship has to turn around and come back) so neither twin is in an inertial frame - General relativity is needed (and indeed on their return both twins will have aged the same amount).

[Evad]

wow :blink: I'll have to read that about 100 more times...LOL

[BeefontheBone]

If you can answer the problem in the middle then you've definitely got somewhere with it. It's basically like the example I did at the top, but with a different unknown quantity (the speed rather than the length).

[Quintopotere]

Originally posted by BeefontheBone@Jun 22 2005, 08:35 PM
A field has no energy of itself, it just generates potential energy in things affected by it, like metal things in a magnetic field, electrons in an electric field etc etc

Probably i didn't explained so well... but when you touch something your matter really don't touch the matter of the thing, cause you only feel a repulsion of the electromagnetic fields of the atoms... and when you look at something you see only the light reflected from its field...
So the existence of matter is not indispensable! We have not direct prooves of its existence, and probaby energy can come in a "matter state" with a property that we call "mass"

Anyway this is a metaphisycs problem that phisycs can't prove...

[Playbahnosh]

Don't go overboard about "a car can't travel with lightspeed/don't exits" and stuff. I KNOW!!!!!!
Man, it was only a "What if..." theory, I was not serious...
It was only in theoretical meaning, I could say that "a lightsourse travelling at almost lightspeed relative to any observer in the innertial frame..." and like that, but a car and headlights was just simpler imaginable so better to understand.
Jeeez, people, be a little more understanding...

[BeefontheBone]

I was being underatanding, just pointing out that the problem could never arise in reality. This is an area of maths/physics where precision is quite important I'm afraid.

[Playbahnosh]

fine <_<
I was only translating this mambojambo to human language that's all <_< For everyone to understand, not just some science moguls like you and other professors...
Sorry if I was too...um...unscientific

[BeefontheBone]

None of that is mumbo jumbo, it's just a bit of maths (simple algebra) with concepts that are presented in A-level physics courses (granted, they don't mention inertial frames, but you can ignore those as a basic assumption in this instance so long as you're wary of accelerating objects). My last post with the examples in it shouldn't be too hard to understand; it's a bit hard to explain in plain text without diagrams though I suppose.

[Quintopotere]

Uh, yes! In phisycs we all know that a good diagram is better than many words!