Question

A) Is there a point where an increasing spring constant no longer affects the bounce height? Why might this be so?

B) How do you think increasing cross-linking in a polymer will ultimately impact the elasticity of the polymer?

Answer 1

AnswerA)Spring constant depends on the surface area(A) and others factors of the substance.

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Lets we take an example here to understand bouncing concept of two different size of balls.

◆If you are comparing a big ball and a little ball that have the same mass, air resistance will slow the big one down more than the small one because the big ball has more surface area for the air to be rubbing against. This makes it seem like the small ball should bounce higher.

To examine the maximum height a bouncing ball attains, ignore external factors such as air resistance,spring constant variation. A ball bounced in place recovers a certain percentage of its original height. {the ball continues to rebound to a height that is 70 percent of the highest point of the previous bounce.}

Answer-B)That crosslinking results in bond formingbetween chains which decreases chain mobility.The decrease in chain mobility means that chains can't flow past one another upon deformation of the bulk. The chain reaches its mobility limit in smaller deformations, causing the external load to strain the chemical bonds (trying to "bend" them). In an un-crosslinked material (especially elastomers), the modulus is driven by the difficulty of chains to flow past one another due to entanglements (think noodles) and also, a thermodynamic drive which we can go into detail if you want (you wanted simple). Crosslinks form a more rigid, non-flowing bulk compared to entanglements.