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Arcade!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Motor Daddy, 19m/s relative to what? I guess you're not going to try my word problem.

Yes, of course!

The distance, for the traveler, is NOT 5ly; It is significantly less.

Not all reference frames are created equal. An accelerated frame is not an inertial one.

It still won't load PDFs for me; I have to download them and view them outside of FireFox.

At least take a stab at my word problem in the other thread.

In the thread about the train problem, the velocity of the train was defined as "compared to the earth the train is moving at 20m/s". The "compared to the earth" bit is important as there is no absolute reference frame. Please stop mixing threads; it makes following them confusing.

This thread isn't talking about trains. No, he didn't. Read the original problem statement in the correct thread.

It's perfectly valid to change reference frames so long as you do the proper transforms.

There are three balls(one red, one blue, and one yellow). Each ball has a mass of 1kg. The red and blue balls are at rest with respect to each other, but are moving with respect to the yellow ball. From a reference frame in which the yellow ball is at rest, the red ball has the energy from mass, but since the red ball is moving, it also has kinetic energy. Now, let's move our reference frame to one in which the blue ball is at rest. The red ball still has the same energy due to mass, but, since it is at rest relative to the blue ball, has no kinetic energy. The red ball has more energy in the reference frame of the yellow ball than it does in the reference frame of the blue ball. Thus energy is dependent on the reference frame and is not conserved from frame to frame. Mass, however is the same in every frame of reference. If we consider the three balls as a system and use the same reference frames, we get different values for the total energy of the system. In the reference frame in which the yellow ball is at rest, there is a certain amount of energy in the system from the mass of all three balls and the kinetic energy of the red ball and the blue ball. In our other reference frame, we have the energy from the mass of all three balls and the kinetic energy of just the yellow ball. As stated, each ball has a mass of 1kg. In the reference frame where the red and blue balls are at rest, the yellow ball is observed to be moving at 100m/s with respect to the red and blue balls. In the reference frame where the yellow ball is at rest, the red and blue balls are each observed to be traveling at 100m/s with respect to the yellow ball. How much [acr=Kinetic Energy]KE[/acr] does the system have?

[math]\Delta{x}'=\Delta{x}\sqrt{1-\frac{v}{c}}[/math]

No, I get smaller if someone is going really fast(in their frame of reference of course). They, in my frame of reference, are smaller than they are in their frame of reference as well.

In a reference frame at rest to me, 2m. In the reference frame of a space alien zooming across the cosmos, about half a meter.

Reality is different in different frames of reference. How many times do I have to ask? RELATIVE TO WHAT? ATFQ

Ok, Motor Daddy, what defines your absolute reference frame?

You still have to make accurate observations.

No. The size of the moon, in your example, is an illusion. You can make an accurate measurement from the same reference frame that disagrees. Hence the numbers change when we change reference frames.

As swansont once said, asking for a speed without a reference is like asking the difference between a duck.

Motor Daddy read the OP for the problem statement.

Relative to what?

If you're so worried, see a doctor instead of making new threads. Internet forums are not a substitute for medical care.

In one reference frame.