Will the book tip more readily if hit by the ball or by the gum?

The chewing gum imparts less momentum to the book: The momentum change of the chewing gum is less because it merely comes to a halt (because it sticks to the book), whereas the super ball changes its momentum a lot since it rebounds. In each case, the momentum change given the projectile is supplied by the book, and the oppositely directed momentum the book obtains determines whether it tips or not. I first saw this demonstrated by Prof. Rory Coker, who fired two darts at a piece of plastic on edge. One dart was tipped with a suction cup; it stuck, and the plastic didn't fall. The second dart was tipped with a superball; it bounced off, and the plastic tipped over. I tried the demonstration myself, and of course it worked.
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