# What is difference between Velocity and Speed?

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I want to know more about physics in game programming and wanna ask what is difference between these two things?

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Speed is a scalar value whereas velocity is a vector. By this I mean that velocity is a combination of a speed AND a direction.

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Velocity is a vector telling how fast and in what direction you are moving.
Speed is a scalar just telling how fast you are moving, it will be equal to the magnitude of the velocity.

In physics you normally just use velocity.

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velocity is a vector
speed is a scalar.
basically the velocity is speed with a direction

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In a practical sense, the above posts are correct. In a computational sense, you will treat speed as the magnitude of a velocity vector. However, the more proper interpretation is that velocity is a measure of displacement over time, where speed is the rate of displacement over time.

In other words, a velocity vector may be used to represent that I've moved twelve meters to the left over a period of 50 seconds, even though my path of motion may not have been in a straight line, and my speed has not been constant.

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In Cartesian coordinates:

x_speed = Δ x position/unit time
y_speed = Δ y position/unit time
z_speed = Δ z position/unit time

Velocity:
v_vec = (x_speed,y_speed,z_speed)

Speed:
s = (x_speed2+y_speed2+z_speed2)0.5 = length(v_vec)

G

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Erissian, you are correct. Many have assumed that speed is simply a scalar, but more specifically its an unsigned scalar. This is because speed is a rate of change in distance over time, while velocity is a rate of change in displacement. Note that distance is an unsigned scalar since distance between two points can never be negative, so speed must also be an unsigned scalar.

Also important, it is defititely wrong to assume that speed is a component of the velocity vector like in one of the last posts.

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