Why do baseball bats break??

Well to make things easier, we are going to use a spring for an example. When you push down on a spring, the force form your push makes it oscillate (move back and forth), and if you don't have any other forces like, gravity or air resistance, it could oscillate forever. If there is enough force being put on a bat, it will oscillate, and oscillation is what cause it to break. Even though objects might be considered inelastic material, like concrete, wood, metal. They still have elastcity, kind of like rubber. What makes them move is their natural frequencey. A natural frequency is a frequency applied through an external force that will generate the maximum amplitude (the size of a wave).
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Bats, they have a natural frequency, and yes they are a hard object, but that doesnt make them "stiff". When a ball hits the the bat, it vibrates, and there will be times where we dont feel it. The vibration depends all on the oscillation. Now bats are not totally symmetric, and there are places where the ball hits that can determine the frequenies and the amplitude. if the ball hits the bat at the antinode will break, if not sting. where the nodes are is where the sweet spot is, and and the antinodes are the head or the mid-point. In conclusion, when the ball hits the bat at the antinode, it is most likely to break.