If I'm driving a convertible at the speed of light and I throw a stone over the windshield...?

Question

Will the stone go faster then the speed of light?

I mean "than" the speed of light

Answer 1

It's a classic example, but it won't work. When you approach the speed of light, time dilates as a result of special relativity. What this means is, you can't be traveling at the speed of light, but you can get very close. Then, when you throw the stone in the opposite direction, you think it's moving fast enough to exceed the speed of light, because in the reference frame of the you driving nearly lightspeed, the stone is moving faster than the amount by which you are moving slower than light. However, this is a trick of the time dilation. In an external reference frame, you are moving only a tiny fraction of the speed you think you are moving relative to the stone, and thus you are still moving below the speed of light.

In another way:

You cannot move at a speed greater than light. This comes from special theory of relativity. If your speed is u and stone's speed is v then relative speed is

not u+v

but (u+v)/(1+uv/c^2) where c is speed of light.

when u v are small even 100km / sec is small as compared to c
this becomes u+v

when u=c we get
(c+v)/(1+cv/c^2) = (c+v)/(1+v/c) = c
and it means that the stone is still going away from you in the speed of light.

Answer 2

OK, just by virtue of driving at the speed of light, you've already violated the speed of light, so let's try doing something that makes sense in the real world. Let's say you're driving your convertible at .9c and you throw the stone at .2c over the windshield. What will your friend standing on the sidewalk see? You might think that it should look like the stone is moving at 1.1c.

The catch here is that because you're moving so fast, you will look shorter to your friend than to you. So while from your perspective, the rock will appear to be moving at .2c, from your friend's perspective, the rock will be covering less distance and will have an overall speed less than the speed of light.

Here's a really fun one which is related on this front: Suppose you're running with a pole which is 20m long at a speed fast enough that to your stationary friends your pole appears to be 10m long. You will run through a barn with doors on each end which is 10m long and your friends will close the barn doors on both sides of the barn just while you're inside.

EXCEPT, that from your perspective, everything else appears to be going the same speed but in the opposite direction, so the barn will now have its length halved so from where you stand the barn is 5m long. So how can the doors be closed on your 20m pole?

It turns out that your perception of time is also changed so that from your perspective, the time at the ends of the poles will be different than what your friends will see, so from your pov, the doors will close on the front of the pole just before it reaches it, you'll burst through the doors and the back door will close after you're already through the barn.

In short, weird things happen when you're moving at relativistic speeds.

Answer 3

Nothing can go the speed of light and if you just throw it over the side of the car then you would not add the velocity vectors of the car and the stone. Darn I took physics last year but according to _____ law no matter what the two vectors you add up are they cannot equal or pass the speed of light.

Answer 4

If you could go the speed of light- the air resistance (friction) would be so great that the stone would immediatly drop. I don't think there's anyway that you would be strong enough to overcome that friction; assuming you were even strong enough to lift your arm to throw the stone in the first place.

Answer 5

No it won't.

Why?

You can't get your convertable to the speed of light, you can get as close to it as you have energy to use to get there, though. When you through your stone forward you might think that your velocity and the stone's velocity might add to more than the speed of light, but you can't add relativistic velocities like you can add them in our common experience.

The formula for adding relativistic velocities is:

w = (u + v)/(1 + uv/c^2)

You will find you can never add two velocities to greater than c.

Answer 6

Every case of study in this matter needs a "refferential frame" as stated by Albert Einstein, so, you have to settle your point of refference first to measure speeds, in ohter words, you have to reffer the speed of car to a fixed point. Have in mind the following, when you aproach to speed of light, your mass grow following a non linear exponential way (this is demonstrated by Einstein in his theory), so you need more energy to continue your aceleration or speed increment, in such a way that when you are almost reaching the speed of light your mass is almost infinite and you will need inifinte energy to reach the final speed of light. But, if your mather changes its form into a beam of light it is possibe reach that speed, but that is not so easy to acomplish nowadays, something by the like is what happends in a thermonuclear reaction.

I expect that this explains something really yet difficult to explain!
Good luck.

Answer 7

Theoretically, since nothing can travel faster than light, the stone you throw won't go faster either. The stone would momentarily stay in the precise spot it leaves your hand before dropping back down due to it's loss of inertia.

Answer 8

no. theoretically you would not be able to move your arm forwards neither backwards because that would be a violation to the constancy of the speed of light as Maxwell said it. (his equations of electromagnetism).

Answer 9

well you would be dead a human can only withstand so many G-forces before being torn apart i think it's around 100G's

Answer 10

You wouldnt be able to lift your arm back to throw it