What is difference between velocity and speed of light?

Answer 1

"Velocity" is a word often used by people who think it's just a fancy word for "speed",

and that they'll sound more knowledgeable if they use the bigger word. The truth is

that the two words have different meanings.

"Speed" means just what you think it does ... how fast you're going, or the distance

you covered divided by the time it took to cover it. Here's the thing, though: You might

travel for an hour at 60 mph and wind up in the next town, whereas I might spend an

hour driving around a circular track at 60 mph and wind up where I started. Both of us

have the same speed, and nobody can tell the difference in our results just from our speeds.

"Velocity" tells how fast, and in what direction. Velocity is speed plus a direction.

-- "30 miles per hour" is a speed.

-- "30 miles per hour north" is a velocity.

-- "50 miles per hour north" and "50 miles per hour west" are equal speeds,

but they're different velocities.

The speed of light is roughly 300,000 kilometers per second.

I personally feel that it hardly ever makes sense to talk about the velocity of light.

It spreads out in a wide fan of directions from most sources. We can bend light sharply,

but it never travels in a circle, and we never have to add together two speeds of light

in different directions to calculate their combination. So the "speed" of light almost

always tells everything you need to know about it. I believe light is a perfect example

of a case where the only people who talk about its 'velocity' are those who know not

whereof they speak.