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
I might be wrong so please correct me.
Glass actually bounces better than rubber assuming it doesn’t break. When glass hits the ground most of the energy of the impact returns to it so it bounces back up. The glass fell down and got a few cracks. When it came down again the few cracks made the glass fragile so it broke.
It probably landed the first bounce on the much thicker bottom. Then turned and landed on the side or upper rim the second time, which is a much more fragile area.
Glasses are much thicker on the bottom so we don’t actually break them just setting them down on hard surfaces during normal usage.
If I remember correctly, it’s related to the material properties of glass. The first impact causes a change in how the atoms are aligned/ bonded (think of a blacksmith hammering metal), resulting in a more brittle material. The second bounce then is able to break it. However, it’s been years from when this discussion occurred, so it might not be 100% correct.
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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