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## Main Question or Discussion Point

hi!

i've been pondering about rotational motion (of a rigid body). i've been doing some internet research on it, but i have some trouble putting things together...

i want to apply forces on the particle parts of a body. one website told me that when you know the axis of rotation, you compute

can i just set

i've been pondering about rotational motion (of a rigid body). i've been doing some internet research on it, but i have some trouble putting things together...

i want to apply forces on the particle parts of a body. one website told me that when you know the axis of rotation, you compute

**r**(the shortest distance between the particle and the axis), then the torque is**t**=**r**X**F**(F being the force). i also learned that motion of a rigid body can be expressed as linear motion + rotation about the center of mass (CM), so i assume that any rotational axis will go through CM.(correct me if i'm wrong so far...)can i just set

**r**=CMP (vector from CM to the particle)? if this is not correct, i wonder how i could know the axis of rotation *before* i know the torque...