Why does the snapped wire create heat?

[Abhishekdas]

Properties of matter...

Homework Statement

A 5m long cylindrical steel wire with radius 2*10^-3 m is suspended vertically from a rigid support and carries a bob of mass 100 kg at the other end...If the bob gets snapped calculate the change in temperature of the wire ignoring radiation losses...
ANd after that some info about density of wire and specific heat and stuff are given...

Homework Equations

The Attempt at a Solution

They have basically equated the potential energy of the stretched wire to heat energy...
But after it snaps why should the potential energy of wire get converted to heat...?
I was thinking it will be an shm...but its having no mass to support so maybe shm is not possible...but still i don't know...why heat?

 

[Abhishekdas]

Any help here??

 

[gneill]

Heat is the last refuge of all energy with nowhere else to go.

 

[Abhishekdas]

ya...i know...but why exactly is not the mechnical energy conserved? before it snapped there was some potential energy...So why doesn't it get converted to kinetic energy of the wire...and then back again...

 

[gneill]

ya...i know...but why exactly is not the mechnical energy conserved? before it snapped there was some potential energy...So why doesn't it get converted to kinetic energy of the wire...and then back again...

Once the wire has thrashed about for a moment, made a whipping sound and vibrated a bit, where is the rest of the energy going to go? Much of the potential energy that was stored in the wire was already associated with the bonds between the atoms in its structure. When the tension disappeared, all those atoms were given a good kick as their bonds all headed back towards their unstrained states, and subsequently the atoms were set to vibrating and otherwise knocking each other about. In other words, heat.

 

[Abhishekdas]

Ok...i did not think of the bonds being broken...and stuff...Ya...your explanation more or less clears my doubt...makes sense...I was thinking i would be kind of and shm...

You know what ...i did a sum where two blocks are initially held my a spring together in equillibrium and then one of the blocks were suddenly removed...Now the spring performs shm...with the other block...that got me into thinking that this was a case of shm...but here i guess its different becase bonds are broken...

But one small thing...in this case had the string not snapped ...lets say the bob somehow slipped out of knot or something...then it would have been shm right?

 

[gneill]

If in stead of a stiff wire where you can't really see the effects of tension on the structure of the material you were to imagine a thick rubber band, would it make much difference to the final state of the rubber how the tension was relieved (either quickly cutting through at one point or dropping the weight)?

 

[Abhishekdas]

i did a sum where two blocks are initially held my a spring together in equillibrium and then one of the blocks were suddenly removed...Now the spring performs shm...with the other block...that got me into thinking that this was a case of shm...

What do you say about this sum...What is the difference between this sum and snapping of a string...When two masses are attached then the mass of the string is negligible...But if the string is snapped then wouldn't the string perform shm with its own mass...Though i exactly don't know what the equations will look like...

 

[gneill]

What is the difference between a string and a wire? In this case nothing if they are both performing the same function, have negligible mass, and snap with the same tension.

 

[Abhishekdas]

Ya...so if masses are not neglible(of the string or wire)...then can it perform shm with its own mass?

 

[gneill]

Ya...so if masses are not neglible(of the string or wire)...then can it perform shm with its own mass?

Sure. But it won't last long because the internal friction eats up the energy very quickly and converts it to heat. It's a highly damped system.

 

[Abhishekdas]

Ok...i guess the picture is getting clearer now...
Learnt a lot from this conversation...thanks man...