What is the difference between speed and velocity ?

The context is Physics

  • In what context? If I remember correctly, in physics, one is scalar and the other is a vector. But in other expressions, e.g., terminal velocity, velocity just simply means speed. – Damkerng T. Oct 18 '15 at 16:47
  • @DamkerngT. i was restudying some physics material, but this time in English, and I went through velocity, that is why i asked – William Kinaan Oct 18 '15 at 16:48
  • Got it! Please edit your question to add that you found the term in your physics books or study materials. The difference is scalar vs. vector. I'll look for some good reference sources and write an answer for you soon. – Damkerng T. Oct 18 '15 at 16:53

Let's start with dictionary definitions:

speed: the rate at which someone or something moves
velocity [physics]: the speed that something moves at in one direction

So, as you can see, in physics, velocity is "speed" and the direction (of something that moves).

Or in an example used by Wikipedia, "Velocity is equivalent to a specification of its speed and direction of motion, e.g. 60 km/h to the north": "60 km/h" is a speed; "60 km/h to the north" is a velocity.

(Because this is an English site, I will not go much into physics. Things could get tricky if we talk about velocity in one-dimension, average vs. instantaneous velocity, angular velocity, and so on.)

That's pretty much about it. However, note that this difference is probably only meaningful in the context of physics, as note in an article by WIRED (with useful illustrations):

But what is the difference? If you ask any person on the street, they might say there is no difference. In non-physics use, they would be correct. However, in physics we have very specific definitions for these terms. Surprisingly, not all textbooks agree on the definition of speed.
(emphasis mine)

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