# set a velocity from zero to a certain value

Hi All,

I know that we can set a velocity to an object, which is made by facet.
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We all know that there is an acceleration process if we want to start a velocity from zero to a certain value.
I want to know how this process comes true.
Is the acceleration a constant value or a changing value? (for instance, the acceleration changes in a sinusoidal wave format)
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Best,
Yong

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 Revision history for this message Jan Stránský (honzik) said on 2021-01-11: #1

Hello,

> I want to know how this process comes true.

From physical point of view in general?
... ?

> Is the acceleration a constant value or a changing value? (for instance, the acceleration changes in a sinusoidal wave format)

??
If "the acceleration changes in a sinusoidal wave format", then it is not "a constant value", but "a changing value"...

please first improve the question itself, then we can give suggestions.

cheers
Jan

 Revision history for this message Robert Caulk (rcaulk) said on 2021-01-11: #2

If you are referring to how a particle can at one time-step in Yade have a velocity of 0 and at the next time-step have a user assigned velocity of V, then you probably need a quick lesson of how Yade integrates particle movement through time.

Have a look at the description of how Yade explicitly integrates particle motion through time using forces [1], and you will realize that in between steps you could simply add a velocity to a particle and it will be reflected in the next time-step. In [2] you see the new velocity is added to the existing velocity state that you would have set manually between steps. Then [3] occurs for the updated particle position. So if you have no acceleration due to forces or gravity in your scene, then the velocity will simply be your user assigned velocity.

In other words, there is no ramp for user assigned velocities.