A similar, simpler problem: Suppose the bat is a

stick, and we hold it at the end $($point P$).$

Where should we hit the stick with a ball so

that it will $($momentarily$)$ rotate about point P

after the collision, without any external force

applied at P$?$ CM

P

FDt

d

The ball applies a brief impulse F$$t $=$ pball

to the stick.

$26$

Example: