Okay, Physicists, speed of light question!

Ricochet J · 14 May 2007 at 17:16

If you throw a ball horizontally forward with speed of 5 m/s whilst you’re in a car constantly travelling at 5 m/s I’ll take the large step and assume the ball accelerates (neglecting apposing forces) and moves 5 m/s^2.

Now, assuming I’m right, if you projected light when travelling at the speed of light, would you get (speed of light)^2 essentially breaking Einstiens law?

(This thread was inspired by the pole communication thread!

)

-|ScottFree|- · 14 May 2007 at 17:18

no

Because nothing goes faster than the speed of light...so Einstein claimed

iCraig · 14 May 2007 at 17:19

-|ScottFree|- said:
no

Because nothing goes faster than the speed of light...so Einstein claimed

Matter cannot go faster than the speed of light. I can't remember if certain waves can be accelerated beyond, or whether it was just hearsay.

cleanbluesky · 14 May 2007 at 17:20

No, the extra energy that the light would get from being projected from a vehicle that is moving would not make it go faster, it would make it increase frequency and therefore change colour

aardvark · 14 May 2007 at 17:21

nothing goes faster than light.

and matter doesn't get close because of its mass.

banja · 14 May 2007 at 17:21

I believe light stays at a constant speed regardless, which is why it's such a head fry.

E+MC2 only works if C, light is a constant. Is that why ilight was labelled C? Perhaps a boffin here knows.

Your initial example reminded me of larks we used to get up to on the tube. If it's empty (or not), take a running jump along a train in the aisle, firstly jumping in the same direction as the train - you'll go about three feet. Then do it in the opposite direction, and you fly about 20

gord · 14 May 2007 at 17:21

This thread is a duplication of the "If my car was travelling at the speed of light and i turned the headlights on, what would happen?" thread.. which im afraid to say was just a better thread.. and also the original.

Ricochet J · 14 May 2007 at 17:22

gord said:
This thread is a duplication of the "If my car was travelling at the speed of light and i turned the headlights on, what would happen?" thread.. which im afraid to say was just a better thread.. and also the original.

I never read that thread

daz · 14 May 2007 at 17:23

Ricochet J said:
Now, assuming I’m right, if you projected light when travelling at the speed of light, would you get (speed of light)^2 essentially breaking Einstiens law?

If you applied galilée transformations at relativistic speeds, you'd get 2 x the speed of light (2c) not c^2

In any case, galilée transformations and newtonian mechanics don't work at relativistic speeds. You have to use the lorentz transformations, and in this, fundamentally the speed of light is the only absolute in each inertial frame of reference. The speed of light is the same for all observers in their inertial frame.

Just to add, special relativity is only applicable in inertial frames of reference (no resultant force == no acceleration) - for other circumstances you need to use general relativity...

gord · 14 May 2007 at 17:25

Ricochet J said:
I never read that thread

IIRC it was on par with the plane on a treadmill, two sandwiches and katana threads.

PinkPig · 14 May 2007 at 17:26

This is essentially the whole point of relativity - light travels at the same speed in all frames of reference. Obviously this doesn't make sense as far as classical physics is concerned, which is where the relativistic equations for additions of speeds and so on come from. For speeds much less than the speed of light, these approximate to the classical equations.

Docaroo · 14 May 2007 at 17:26

firsty surely you don't multiply the two speeds but simply add theM?

secondly, light is a constant so if you are travelling at say, 1/2 the speed of light - light APPEARS to move at the exact same speed as if you were standing still... that is why it's a bit tricky to comprehend....

It gets far more complicated than that though

iCraig · 14 May 2007 at 17:29

When I was reading about the theory of relativity, I soon learnt that traditional thinking had to go out of the window at 12 m/s rather than the usual 8 m/s.

Amleto · 14 May 2007 at 17:32

iCraig said:
When I was reading about the theory of relativity, I soon learnt that traditional thinking had to go out of the window at 12 m/s rather than the usual 8 m/s.

eh?

Psyk · 14 May 2007 at 17:33

banja said:
Your initial example reminded me of larks we used to get up to on the tube. If it's empty (or not), take a running jump along a train in the aisle, firstly jumping in the same direction as the train - you'll go about three feet. Then do it in the opposite direction, and you fly about 20

If the train is going a constant speed, it shouldn't make a difference which way you jump. But a tube train is probably accelerating or decelerating during most of the journey.

cleanbluesky · 14 May 2007 at 17:33

iCraig said:
When I was reading about the theory of relativity, I soon learnt that traditional thinking had to go out of the window at 12 m/s rather than the usual 8 m/s.

With the move to Quantum Theory, traditional theory also assumes a frequency of 7

banja · 14 May 2007 at 17:35

Psyk said:
If the train is going a constant speed, it shouldn't make a difference which way you jump. But a tube train is probably accelerating or decelerating during most of the journey.

Maybe it shouldn't, but it does.

iCraig · 14 May 2007 at 17:35

Amleto said:
eh?

You see, you're already lost. Wait until you get into the intricate details of quantum mechanics and the Sugababes particle.

Psyk · 14 May 2007 at 17:38

banja said:
Maybe it shouldn't, but it does.

lol well that must mean the train is accelerating to a certain extent, even if it's not really perceptible.

Amleto · 14 May 2007 at 17:41

iCraig said:
You see, you're already lost. Wait until you get into the intricate details of quantum mechanics and the Sugababes particle.

since I'm lost, does that mean I know exactly what my momentum is?