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Name: Robert A Kinson
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Question:
I could use information on why silly putty bounces and why Jello jiggles in relation to polymers. Thanks.



Replies:
Silly putty is made of long flexible molecules all tangled up. If you just let the putty sit or smoosh it with your fingers, the molecules slide over each other and the material flows. When you drop it, the impact tries to make the molecules move past each other very fast. They can't do this, they're too tangled, so instead the molecules deform, like stretched and compressed slinkies. Then after the ball stops, they rebound to where they were, and this generates the force that causes the ball to bounce up. Jello is also made of long flexible molecules tangled up (with a lot of water in between), but in this case they're also attached to one another, so they can't move past each other at all. So Jello won't flow no matter how slowly you moosh it. All that happens eventually is that the molecules or the junctions break, or more complicatedly, the network slips along a fault, and the Jello rips or crumbles.

Christopher Grayce



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