I dropped a glass yesterday, from waist height on to a tiled floor. It bounced and then when it hit the floor again it smashed. Why didn’t it smash the first time it hit the floor?
In: 17
Impact one causes the glass to start vibrating, which causes lots of acceleration forces in the material. Impact two happens and doesn’t match the phase of the existing oscillations and results in high instantaneous accelerations, which result in higher stresses and the glass breaks.
That, and often it depends on orientation. First impact might be on the bottom of the glass which is heavier. It bounces and rotates a little. Second impact is out towards the rim of the glass where it’s thinner/weaker, and it’s rotating into the ground. Angular acceleration can be deceptively strong (i.e. difference between stepping offer a 10ft falling ladder versus staying on and hitting the ground at a higher speed because of the rotation.)
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