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I have a equation i need to find out how they hang together.

angel = (velocity * time) - (acceleration * time * time / 2)

I know circumference of a circle:

2*Pi*radius -> (velocity * time)

radius is:

(velocity * time) / (2 * Pi)

But. What is this mean:

(acceleration * time * time / 2) 

I think It's look like some kind of velocity.

Any idea ?

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It's the angular displacement caused by angular acceleration. – Frenzy Li Nov 26 '12 at 12:45
up vote 2 down vote accepted

From what I could figure, you are in the case of circular motion with constant acceleration see Wikipedia

Be careful with your notation, because in this case there are 2 velocities, angular and linear. Angular is independent of the radius (usually denoted as $\omega$) while linear is actually $\omega\cdot r$.

So, probably in your first equation $\theta=\omega\cdot t - \frac{1}{2}a t^2$ you are mixing linear and angular quantities.

In any case, to answer the last part, $a$ is the acceleration, i.e. second derivative with respect to time of the angle $\theta$, $\frac{d^2\theta}{dt^2}$, and describes how the angular velocity changes with time. The $\frac{1}{2}at^2$ is a straightforward derivation from the equations of motion for constant angular acceleration.

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Thanks, will look into it! – Neru-J Nov 26 '12 at 13:32

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