steel is more elastic than rubber.why?

Question

farcher · Answer

A perfectly elastic material is one which returns to its original shape and size after deforming forces are removed.  Also all the energy which is used to deformed the material is recovered when the material returns to its original shape and size.

anonymous · Answer

^^ you didn't help him answer his question :P

what Farcher said is true.. 
but how do you decide which is MORE elastic?
well the one which returns to original shape and size FASTER is said to be more elastic..

that depends on the MODULUS of elasticity yea?
so now can you think why steel more elastic than rubber?

farcher · Answer

In pure energy terms then from what I have written above the steel is more elastic for the following reason.
Whilst both materials return back to their original shape and size after the deforming force is removed the rubber does not give back all of the energy which was stored in it after it was stretched.
It suffers what is called a hysteresis loss.  One cycle of compression and then release results in some of the stored energy becoming heat.  This is loss that all car tyres suffer and so some of the fuel used to make a car move is used to heat the tyres.  If you watch Formula One racing you know this to be true as tyre temperature is vital to the performance of the cars.  In the main the tyres do not get hot due to the tyre slipping relative to the road rather it gets hot due to hysteresis.

On the other hand you compress a piece of steel and then release it.  You get all the energy back and the steel stays at the same temperature.

anonymous · Answer

Farcher.. thats not necessarily true.. 
every material will undergo deformation once you start deviating from the hooke's law region, then you won't get all the energy back, some of it is used in being permanently deformed..

anonymous · Answer

This question usually arises because, we have a misconception about the word elasticity, 

we tend to think that if we can deform something easily , (and it returns back), then it is more elastic.. 

but in reality, its opposite.. more difficult something to deform , more elastic it is, cause.. we define elasticity as the ration of stress/ strain

that means, for highly elastic material, we need more stress per unit strain (difficult to strain a material)..

farcher · Answer

@Mashy 
I agree with you assessment when the deforming forces become such that the elastic limit is exceeded.  However even for small deformations rubber suffers a hysteresis loss.

Elastic in collisions means kinetic energy conservation it  has nothing to do with any modulus of elasticity.

anonymous · Answer

Yes.. that is because rubber bands do not obey hookes law AT ALL 

And elastic collisions also have something to do with modulus of elasticity.. 
Kinetic energy can only be recovered as long  as it can be stored as potential energy (during a collision), this potential energy is nothing but elastic potential energy, which is purely dependent on the elastic properties!

farcher · Answer

Steel obeys Hooke's law up to the limit of proportionality.
Beyond that it still behaves elastically until the elastic limit is reached.

Another way of looking at the question is to compare a modulus of elasticity and then perhaps a material is more elastic if it deforms more for a given applied stress.
On this definition rubber would win.

anonymous · Answer

"Another way of looking at the question is to compare a modulus of elasticity and then perhaps a material is more elastic if it deforms more for a given applied stress.
On this definition rubber would win."

But that is not how we define it at all :P.. its not how much strain you get per unit stress.. 
that definition of elasticity wouldn't make much sense, if you think about it!

farcher · Answer

I am pointing out that the original question cannot be answered unless the definition of elastic if agreed.

anonymous · Answer

well.. there is only one international definition of elasticity Buddy.. and that is Stress per unit strain!

farcher · Answer

I don,t deny there is a defininition of elasticity but the point I am making is that the question used the word elastic which has a very different definition.

anonymous · Answer

Why do you think so?
According to that definition itself, Steel is more elastic than rubber..