Speed relative to light (relativity effects)?

Question

If you have two objects travelling opposite directions and one is going 3/4 the speed of light say north (just for direction) and 3/4 the speed of light south. Wouldn't the objects be going faster than the speed of light for the observers. So what would the relativistic effects be on length time and mass.

Answer 1

This is probably going to be WAY off base, but this is how I understand it, given your example:

The faster the north and south ships go, the more space-time will "stretch", but time will continue as normal as far as the individual pilots are concerned(think of "space" as stretching & holding them back like tar).  This means that even though they will not travel as far as they should with the distance-time equation, when they return to the point of origin, their wristwatches will indicate that much more time has passed than should have for the distance that they thought they travelled.

SO when you say that they should look like they are going 1.5x the speed of light, they will never be going more than the speed of light.  The elasticity of space-time will hold them back and only make them look as though they are going 0.99x the speed of light (or whatever the fancymath resolves to, hehe; sorry, I didn't think to add math to this).

EDIT:  Also, not that I really know anything about that whole E=MC2 thing, but I figure that according to the math, the mass will decrease as more energy is expended to accelerate the object.  Think of a rocket burning fuel:  the rocket fuel is burned (mass decrease) to make the rocket go faster (more energy removed from accelerating the rocket).  Then again, I have probably been watching way too much Star Trek, ha ha.

Answer 2

The best possible answer to this is that never ever mix up Newtonian/Classical Physics with Relativistic Physics.

Obviously you have never applied the speed of light concept to Newton's First,Second and Third Law. Then why did you at all try incorporating Newtonian Physics in the speed of light concept.

First thing, even if 2 objects were moving towards each other at a speed that tends to c, each object would always see the others speed to be at c.

Don't try to bring the concept of relative velocity into SR theory. It's 2nd law clearly states that nothing, that can be stationary and have a rest mass, move faster than c. Only objects like Tachyon that inherently move faster than c can do the feat. Even for them there is a limiting factor - their speed can't come below c.

Answer 3

No, to an observer riding on one of the objects, the other is travelling at

(.75 + .75) / (1 + .75*.75)

= 1.50 / 1.56

= 0.96

To that observer, the track along which the Earth observer was measuring the motion is contracted, so there is less distance covered by the separating objects. That observer also observes Earth's clocks running too slowly, so that one second on that clock is several seconds on his own. So the bodies separate by less distance in more time. In particular, they separate at 0.96c.

Answer 4

No. At near light speed, velocities don't add the same way you are used to adding them, but by the following equation:

w = (u + v) / (1 + uv /c²)

Notice that when u = v = c, the relative speed becomes:

w = (c + c) / (1 + c*c/c²)

w = 2c / 2

w = c

In your case it's:

w = .75c + .75c / (1 + (.75c)²/c²)

w = 1.5c / 1 + 0.5625

w = 1.5c / 1.5625

w = 0.96c

You would each observe the other as going at .96c, and a 3rd observer would see each of you going at .75c.

Answer 5

No... you are entering into Relativistic Velocity addition.

V =  (u+ v)/(1+uv/c^2)

have you learnt this equation???  This will answer your question.

Where u is the speed of earth relative to ship 1, (+0.75c) ** this requires a bit of thinking.....

v is the speed of ship 2 relative to earth  (+0.75c)

and V is the speed of ship 2 relative to ship1.  (unknown)

As for time: both observers will age slower than the observer on earth..  For length, the observers on the ships will see each other's ships to be shorter than it's stationary length.

and Mass... each observer will see that each other's mass is increased.... (if that's possible to observe...)

Answer 6

no.  it's relative.  time slows mass decreases