# Velocity?

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does a velocity of zero exits in the universe, or any velocity apart from the speed of light, since everything is relative to something else, how can i say i am moving faster or slower than another object with confidence?

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If my velocity is x and another body's velocity is y, then-

If both are moving in same direction - if xt>yt, I am moving faster. If xt<yt, I am moving slower. (t is a specific time interval)

If moving in opposite direction- take reference point P, and then analyse similarly.

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does a velocity of zero exits in the universe, or any velocity apart from the speed of light, since everything is relative to something else, how can i say i am moving faster or slower than another object with confidence?

It comes down to choosing from which point of view you want to look at a problem from. The observer you choose is typically assumed to be stationary relative to the other inertial frame. If need be, you can then swap observers to get another other point of view.

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does a velocity of zero exits in the universe

All velocity is measured relative to something. If something is not moving relative to you, then its (relative) velocity is zero.

how can i say i am moving faster or slower than another object with confidence?

All velocity is measured relative to something. If something is moving slower than you relative to some (arbitrary) reference, such as the ground, then you are moving faster than it. And vice-versa.

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since light speed is a constant why dont we measure velocity relative to it

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since light speed is a constant why dont we measure velocity relative to it

Because it will always measure at c, regardless of your own velocity. This is a central tenet of SR. If it always measures the same, how can you use it to gauge velocities of things relative to it?

Edited by StringJunky
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Kind of a basic question, but doesnt the fact that it always measures the same make it the perfect datum, please correct my misconception

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Kind of a basic question, but doesnt the fact that it always measures the same make it the perfect datum, please correct my misconception

It's always the same relative to the person measuring it.

Let's say that you and another person are moving at 0.5c with respect to each other. at the moment you pass each other, a flash of light is emitted from your position.

You will measure the light as moving at 299,792,458 m/s away from you in all directions. The other person will also measure the light as moving away from them at 299,792,458 m/s.

If you could use light speed as an absolute reference, only one of you would be able to make that claim and the other would measure the light moving at 149,896,229 m/s in one direction relative to himself, and 449,688,687 m/s relative to himself in the opposite direction.

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