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# Calculate force for torque by specifying a required velocity

I am able to calculate a force using a required velocity and apply this to a Rigidbody using AddForce. After a lot of investigation, I stumbled across the answer in Unity's forums, here is the working equation:

```
Force = (speed / 2) * mass
```

**I now want to do something similar to rotate a Rigidbody using AddTorque. Nothing I've come across comes close to this method. Please help.**

P.S. It is important that I calculate the force required, which eliminates using ForceMode.Acceleration.

you need a reasonable grasp of junior high physics for this,

nobody on this list can do even arithmetic :)

First arm yourself with an understanding of rotational inertia,

http://en.wikipedia.org/wiki/List_of_moments_of_inertia

then I suggest you ask your specific Torque question on the "math.stackexchange" site

you will instantly get many detailed smart-arse yet useful answers from wannabe undergraduate college kids

eg, http://math.stackexchange.com/questions/168172/torque-calculation-to-achieve-clean-spintumble

http://www.angelfire.com/nc3/pweb/lessons/torrotin.htm

conceivably somewhere like gamedev you could get an answer also

Hope it helps in some way!

Again you can't ask the question until you know or decide on the moment of your object.

Thanks for taking the time to answer. Having looked into this there seems to be hidden key element which AddTorque() uses. That is the radius from which the force is applied. Given that, I think I need to find a Physics guru who uses Unity...

**Answer** by centaurianmudpig
·
Feb 24, 2013 at 12:25 AM

The solution to my problem seems too simple but it works...

**Force = Speed / Time.fixedDeltaTime**

i.e. A rotation speed of 1.5 required a force of 75.

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