Knight Rider Physics II, sorry PhillipY...

Factual Questions
1

After reading this thread and pursuing this link in that thread, I offer the following question using this quote as the basis.
From mrbuddylee;
"another part of my brain however argues this point (which I don’t know the answer to). Lets assume we have a super fast jet sled in the desert going about 500 mph. Lets say it’s 100 ft long. On that sled, we have another model sled that’s 6 in. long. It can go 300 mph (We’re in theory world, not the real one). Now, does the second smaller sled break the sound barrior on the back of the larger sled while the first one doesn’t? I would think so, but I don’t know… ".

Could such a model be built that could feasibly break the speed of light? Build a super long vehicle that gets up to 3/4 light speed. On it would be a very long vacuum tunnel that would house another smaller vehicle that could also approach the 3/4 speed of light mark. That smaller vehicle would break the speed of light, no?
For the sake of this thread let`s assume this experiment is done in the nether reaches of space somewhere (making the vacuum tube probably unnecessary).

2

No, because of that pesky massincrease at relativistic speeds. When you’re vehickle reaches exactly c its mass is infinite and no amount of energy will accelerate it anymore.

3

“Vehickle”? How 19th century is that?

4

Mm, Q.E.D.'s remark suggests that there’s some magical wall at C that you hit, velocity wise, and then stop. This may have just been simplified for the sake of the post, but I’ll nitpick a moment – you never reach C, and your ‘relativistic mass’ (which is evidently an old and somewhat deprecated term) increases as your velocity increases all the way along. It happens to grow very rapidly closer to C, and is asymptotic to the vertical line at C (shoots towards infinity).

You can get as close as you like, naturally, if you’re willing to put the energy into it. You just can’t reach that speed.

Please do a message-board search about the speed of light to see the hundreds of pages of relevant discussion about how you can’t break the speed of light by simply adding velocities like whuckfistle is proposing. (Velocities don’t add linearly near the speed of light, obviously).

5

From what Q.E.D said, it sounds like the speed of light is like the wall of an infinite square well. So, couldn’t there be some sort of quantum tunneling effect that would allow a vehicle to go faster than the speed of light?

6

I didn’t mean to imply that the speed of light was some instantaneous barrier. I was only pointing out why it cannot be exceeded. As William_Ashbless points out, even before c is reached, the mass gets so large that impractically large amounts of energy become necessary for further acceleration, so no massive object can actually even reach c.

7

Why do light photons have such an easy go of it then?

8

Cause they have zero mass.

9

As long as were on the topic,- what is our current speed (here on earth) relative to the speed of light?

There must be a reference of zero somewhere.

10

There’s no absolute reference. This was one of the things that Einstein got so famous for.

My dad’s favorite pesky phrase is, “Relative to what?” You have to pick a reference point, kind of at random.

If you walk on the moving train, are you going 4 mph, or 54 mph? It depends on if you are measuring relative to the train, or the ground.
My question is, are we possibly moving very close to the speed of light relative to another star or planet that’s hurtling in the opposite direction? If not, is that because there wasn’t enough energy in the Big Bang to do that? If we are, what are the implications of that?

11

Nope. The whole point of relativity is that there is no universal reference. Velocities only have meaning when measured relative to something.

12

I understand the relative thing, mostly.

Like Cardinal said,
What if the planet is moving at close to the speed of light already. In reference to nearby stars and such, that is. There could be several (an infinite number really) such instances in the universe where the speed of light is relative to the nearest beings that are observing it.
How do you tie together their observations with our observations if each being observing is taking measurements in realation to their own environment. If the observed measurements are realtive than how can the speed be a constant?

13

Anyone catch the pun here?

Hint: It has to do with QED`s answer.

14

The observers all agree that the speed of any given photon in a vacuum is the same. They will disagree about the exact wavelength of it, though.

This is not intuitive, but this is what will happen. Say there was one observer on a train which was traveling at, say, 0.5c with respect to another observer on the ground.

The observer on the train then pulls a laser pointer from her pocket and shines it in the direction the train is going. Let’s say the laser emits a red beam, say, 700nm.

The observer on the ground, then, will see the beam travel at c, the speed of light, assuming that the train was travelling in a vacuum. However, he would see a beam of a different wavelength.

The formula for the wavelength shift is:

w’ = w(1 - cos(phi)v/c) / sqrt(1 - v[sup]2[/sup]/c[sup]2[/sup]) [sup]Cite[/sup]

…where phi is the angle between the direction of motion and the beam of light, and v < 0 means that the motion is towards the observer, and v > 0 means that the motion is away from the observer.

So, when the train was traveling straight towards the observer on the ground, he would see a beam of wavelength 700nm [sup].[/sup] (1 - .5)/sqrt(1 - 1/4) = 404nm, which would appear blue.

When the train was receding, the observer on the ground wouldn’t be able to see the beam. First, because the apparent wavelength would now be 1212nm, which is in the infrared spectrum. Second, because for the observer to see the beam on the approach as 404nm, he must have been standing on the tracks.

15

Whilst we are on the speed of light - perhaps someone can help me with another problem I’m having concerning reaching the speed of light.

If you were in a vacuum with a really long piece of material (steel for want of an example) what is to stop you cutting a 2km length and spinning it round 25 times a second. If my maths is correct that would mean the end of the rod was travelling round a distance of 12566370m each time. Therefore it would travel 314 million meters per second - faster than the speed of light.

Even if my maths is off, what is wrong with the concept?

16

Exactly the same problem - as the end of the rod got up towards c, its mass would increase, thus requiring more and more force to accelerate it further.

17

See previous threads. All these questions have been answered dozens of times.

18

Muttrox,

19

[must look at screen when typing else likely to hit send button and not realise - sorry about that]
Muttrox,

I’ve tried looking in the archives under speed and light and circle, speed and light and rotate but no joy. Can you provide me a link to the appropriate discussion?

TIA

20

yes, this has all been answered b4, but still

and i think it is in a few more threads, but still

ianlyte, your problem in this case is that it would require an ever increasing amount of energry at the axis of the spin to make it spin faster, and you would never be able to reach a speed of 25 spins per second(Hz?).