# Perfectly elastic and perfectly inelastic rope behavior

I understand the meaning of transverse and longitudinal waves, but I'm still confused with the edges of elasticity, like perfectly elastic, and perfectly inelastic. Elasticity (to me) has to fulfill 2 conditions as described here, the body must resist a distorting influence and must return to its original size and shape when that influence or force is removed.

So a perfectly elastic object will have a super resistance that it won't bend at all? And in this case the second condition won't have a chance to be applied - thus even if the force is removed?

While a perfectly inelastic object will absolutely deform with no resistance at all, and when the force is removed, will get directly back to its original shape.

Recalling the experiment of a rope, fixed in one end, and in the other end moved up and down fast vertically (back to the original horizontal level). Let's discuss the 2 extreme cases and whether a wave will happen or not in simple terms please without introducing formulae.

The motivation behind my interest in the "elasticity" topic is one sentence I read in my student's book which says that elastic waves can be transverse and longitudinal. I can imagine a longitudinal wave (the horizontal spring example), but was interested in the case of transversal elastic wave, thus started to ask whether the transverse wave can be elastic; which it can. So I thought that understanding the extreme cases of elasticity can help. But we can leave that to another question.

• Re, "A perfectly elastic object will have a super resistance that it won't bend at all?" No. That's not what "elastic" means. A perfectly elastic object does not have to be perfectly stiff, but it does have to give back all of the energy that was used to deform it. A perfectly inelastic object, on the other hand, can resist deformation, but when you do deform it, it gives no energy back. Jan 14, 2020 at 15:25
• Yeah, I felt so, the "must resist" part doesn't have to be infinite. Jan 14, 2020 at 15:28
• I think there is some confusion in that that's not 2 conditions, it's one, and it should be inferred that when they say distorting, they mean permanent.
– user234190
Jan 14, 2020 at 16:06