Hi there,

I just visited a homepage on one of our public service channels regarding a
TV show about relativity. The home page explains the RT, but I find it a
little contradicting in terms of the "speed of light" constant.

I quote and translate:
--------------------------------------
A question about relativity
An objects speed normally depends on how fast the object itself moves. If a
trains runs at 100km/h we suggest that it runs with 100km/h in respect to an
observer standing outside.

If a person on the trains throws a ball forward with 10km/h, the observer
outside would measure that the ball moves at 110km/h, the ball plus the
train speed.

If we point a flashligt in the forward direction the light will now run with
a speed of 1.000.000.000 km/h, so the observer outside should logically
measure 1.000.000.100 km/h.

But it was exactly this change that the physicians at the time of Einstein
were unable to measure.
---------------------------------------

My question:
In other words the speed of ligth is constant, even in different inertial
frames (train / observer). Say that the trains was running at ½ the speed of
ligth. Will the observer still be measuring 1.000.000.000 km/h?

The reason I ask is that in some of the other material the speed of ligth is
referred to as being constant to the "senders inertial frame". In my
thinking this means that the
observer would be measuring 1½ times. Now it we run two trains side by side
at ½ the speed, what will the speed of light measure in between them 1x?
If the trains where running on the same track, one behind the other 1x?

It's a little contradicting to me. Would it be right to express the speed of
ligth to be constant within the universe, and no matter how fast you are
going the light is always at the same speed. Like if light was sound waves
and we had different observers and sound sources with different speeds, the
speed of sound would always be the same to any observer.

If I got all this is wrong I need another place to look up some information
which clearly states the idea's behind RT - links are appreciated.

Regards
K. Ellested

Dear Kenneth Ellested:

"Kenneth Ellested" wrote in message
. ..
Hi there,

I just visited a homepage on one of our public service channels regarding
a TV show about relativity. The home page explains the RT, but I find it
a little contradicting in terms of the "speed of light" constant.

I quote and translate:
--------------------------------------
A question about relativity
An objects speed normally depends on how fast the object itself moves. If
a trains runs at 100km/h we suggest that it runs with 100km/h in respect
to an observer standing outside.

If a person on the trains throws a ball forward with 10km/h, the observer
outside would measure that the ball moves at 110km/h, the ball plus the
train speed.

If we point a flashligt in the forward direction the light will now run
with a speed of 1.000.000.000 km/h, so the observer outside should
logically measure 1.000.000.100 km/h.

299.792.458 m/sec or 1.079.252.848 km/hr

But it was exactly this change that the physicians at the time of
Einstein were unable to measure.

"Physicists". "Physicians" are doctors of medicine.

---------------------------------------

My question:
In other words the speed of ligth is constant, even in different inertial
frames (train / observer). Say that the trains was running at = the speed
of ligth. Will the observer still be measuring 1.000.000.000 km/h?

The train might travel vanishingly close to the speed of light, compared to
any particular reference frame, but never "at the speed of light". But any
detemination of light speed that is made will always return c for a two-way
round trip (the only determination possible).

The reason I ask is that in some of the other material the speed of ligth
is referred to as being constant to the "senders inertial frame".

Maxwell requires the same speed for all devices, the emitter, and the
receiver of the light as well. Relativity only states that all the laws of
physics (including Maxwell's description) are the same for all inertial
observers.

In my thinking this means that the
observer would be measuring 1= times. Now it we run two trains side by
side at = the speed, what will the speed of light measure in between them
1x?

In a vacuum, c.

If the trains where running on the same track, one behind the other 1x?

In a vacuum, c.

It's a little contradicting to me. Would it be right to express the speed
of ligth to be constant within the universe, and no matter how fast you
are going the light is always at the same speed. Like if light was sound
waves and we had different observers and sound sources with different
speeds, the speed of sound would always be the same to any observer.

Right.

If I got all this is wrong I need another place to look up some
information which clearly states the idea's behind RT - links are
appreciated.

URL:http://hermes.physics.adelaide.edu.au/~dkoks/Faq/
.... down to the section "speed of light".

David A. Smith

Kenneth Ellested wrote:

Hi there,

I just visited a homepage on one of our public service channels regarding a
TV show about relativity. The home page explains the RT, but I find it a
little contradicting in terms of the "speed of light" constant.

I quote and translate:
--------------------------------------
A question about relativity
An objects speed normally depends on how fast the object itself moves. If a
trains runs at 100km/h we suggest that it runs with 100km/h in respect to an
observer standing outside.

If a person on the trains throws a ball forward with 10km/h, the observer
outside would measure that the ball moves at 110km/h, the ball plus the
train speed.

If we point a flashligt in the forward direction the light will now run with
a speed of 1.000.000.000 km/h, so the observer outside should logically
measure 1.000.000.100 km/h.

But it was exactly this change that the physicians at the time of Einstein
were unable to measure.
---------------------------------------

My question:
In other words the speed of ligth is constant, even in different inertial
frames (train / observer). Say that the trains was running at ½ the speed of
ligth. Will the observer still be measuring 1.000.000.000 km/h?


Yes. By the way, I'm not going to explain stuff that you found
on some website just because that website purports to explain
relativity. I may not agree with the other stuff that was posted.

John Anderson