angular momentum / torque

[mrbill]

What's the difference between T = r X F and T = I(alpha)? My book really sucks it up with the explanations. Both make sense to me. The answer is right in front of me im sure, but im just not catching it. One is merely an expression of Newton's second law? Bah, it cant be that simple!

MrBill.

[Doc Al]

Originally posted by mrbill
Bah, it cant be that simple!

That's pretty much it. T = r X F is the definition of torque; T = I*α is Newton's 2nd law for rotational motion.

[ShawnD]

There is no difference, they're just 2 formulas relating to the same; that's why the two formulas can be set equal to each other in order to solve for a certain variable.