# Force and Torque Question on an isolated system

If there's a rigid rod in space, and you give some external force perpendicular to the rod at one of the ends for a short time, what happens?

Specifically: What dependence does the moment of inertia have? If it rotates, what is the center of rotation? Does it matter that the rod is rigid? What happens if it's "springy", say a rubber rod instead. Is there a difference between exerting a force for a short period of time, and having an inelastic collision (say a ball hits the end of the rod instead of you pressing).

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The second answer here is helpful: physics.stackexchange.com/q/43232 –  chase lambert Jan 15 at 11:21
What is the center of rotation though? –  chase lambert Jan 15 at 14:15
The moment of inertia of a rod with a perpendicular axis of rotation through the center of mass is $$I=\frac{1}{12}ml^2$$ where m is the mass and l the length.
If you apply a torque $$\tau=r\times F$$ (all vectors), then $$\tau=I\alpha$$ lets you calculate the angular acceleration alpha.