# better understanding of velocity

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If velocity is the movement of an object over a period of time in a given direction how does @v correspond to time/distance?

Say I had a ball with a velocity vector of {0,1,0}, how many units in the y axis should I expect the ball to travel per unit of time? I'm assuming it's 1m/s?

(after I posting and seeing the question I realized that this is a pretty easy thing for me to test out)

Edited by shawn_kearney

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@v (or any velocity) is an instant velocity, meaning at this point of time this is the speed at which an object travels, its unit is : meter/second (you can have any unit, but houdini default units are meters and seconds)

if v= {0,1,0} then it means that the object goes up one meter per second (so if it's at (0,0,0) at time = 0 second, then it will be at position (0,1,0) at time = 1) . Note that it's per second, and not per frame, because it depends on your frame rate, you could have 24 Frame Per Second (FPS), which means each frame is 1/24 second, or you can configure houdini to assume 30FPS.

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Yes, a sphere with velocity 0,1,0 will move one houdini unit upwards in one second. And one second is the FPS of the scene, so for example it will move 1/25 of that velocity per frame.

This is without any other forces of course. If you are doing it in a simulation you will have gravity, friction etc. so all that will matter too.

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You can also throw down a time shift and grab the velocity from a future or past frame. Subtract now from then to find the amount of velocity change between the two frames.

Edited by Atom

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if you start playing with @v in wrangles or vops, you should also consider @TimeInc to help normalize your velocities.  @TimeInc is the length of the current step, which is normally 1 frame length (1/\$FPS), but will adjust for subframes.  if you add @v to @P, multiplying @v by @TimeInc will provide a consistent result no matter what frame rate or sub frame stepping you use.

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