Thread: Torque?
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Unread 08-12-2011, 20:05
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Re: Torque?

Quote:
Originally Posted by CalTran View Post
So, in Physics, we just started learning about Torque, and I was wondering if there was a simpler explanation than the one given by my teachers about inertia being equal to weight and what not. Would anyone be able to explain it in simpler terms?
The way I understand it is a force applied at a distance from the axis of rotation in such a way that the object rotates. That's the nice and easy Fxr version. (I think about the cross product in terms of finding the component of force that is perpendicular to the moment arm, which requires the sine function hidden in the cross product. The direction of torque is something like the side from which the rotation would look counterclockwise, but that's a little less important than the magnitude) The easiest example to understand is a door. You apply a given force at any point on the door, and your ability to move the door - i.e. the torque - is dependent on the angle of the force (parallel to the door would obviously not move it) and the position of the force (near the hinge is harder than near the knob).

Now, force equals mass times acceleration, and acceleration equals angular acceleration times radius. So substitute and now you have Amr^2 (just pretend that A is alpha), but that really only applies to a point mass. What you actually have is the sum of all the little bits of torque. That's equal to the sum of all the little bits of mr^2 (or the integral of r^2 dm if you have an understanding of calculus), which is I, multiplied by A which is the same for all the particles.

So torque is moment of inertia times angular acceleration. That doesn't really explain the F=ma and tau=IA analogy, but I hate that, too.
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Last edited by Ninja_Bait : 08-12-2011 at 20:10. Reason: I wanted to make more sense.