Noise - really geeky question

[Bri w]

Why do different things make different noises when you hit them?

Happened to bash a really solid peice if metal today, and it made the sort of noises you'd expect but why?? Why do the sound waves from a block of metal make a different noise from something equally solid like a block of perspex.

I know, I need to get out more...

[kaivalagi]

Not being a material scientist or anything I would assume it has everything to do with the molecular structure i.e. the type of atoms, the materials density, the bonds between atoms etc and how this has an effect on the air around it and therefore the sound made

May be totally wrong.....but being equally sad I am now going to look for evidence if there is such a thing

molecular vibration.
Similar principal as to why a steel ball will bounce higher off a steel block than a rubber one off a rubber block...
discuss

sound waves refect off and pass throught the differnt molecular structures in different ways , eg, tighter spacing of molicules more risistance, thefore changing the frequincy of the resulting sound

[kaivalagi]

Originally Posted by Kilted Ginger

molecular vibration.
Similar principal as to why a steel ball will bounce higher off a steel block than a rubber one off a rubber block...
discuss

The rubber block absorbs and disperses more equivalent kinetic energy of the rubber ball as it has more flexible/loose bonds than the steel block and ball?

I'm finding some great youtube vids

edit: quantum physics around molecular vibration

Originally Posted by Kilted Ginger

molecular vibration.
Similar principal as to why a steel ball will bounce higher off a steel block than a rubber one off a rubber block...
discuss

also with this , item compression on the molecular level is taken into account, nothing is completely solid and when 2 things touch the actually join together and move (compression) but due to the packing of the molecules and the attempt to rejoin there orginal shape at different speeds and force, add in elastication (transfer of forces from forward movement to rearward) and that for every action there is an equal and oppisite reaction, the forces change depending on hundreds of variables

Its pretty cool how many sounds can be achieved through different things.
Me being a drummer (did you guess?) im always tapping on things, i cant help it, i spend all day drumming and tapping on my knees, tables, handlebars, doors, you name it, i do it without even realising sometimes, not with drumsticks, but just with my bare hands like the world is a giant bongo drum. But i love how so many things produce different sounds.

Interesting to know the science behind it. Ive always got different sounds out of different things. Such as on an actual drum there are so many sounds on just one drum, depends where you hit it, how hard and what with. Same for cymbals, so many possibilities on what is basically just a piece of metal thats been hammered by a bloke in a factory until it makes a certain sound.

[yorkie_chris]

Originally Posted by Bri w

Why do different things make different noises when you hit them?

Happened to bash a really solid peice if metal today, and it made the sort of noises you'd expect but why?? Why do the sound waves from a block of metal make a different noise from something equally solid like a block of perspex.

I know, I need to get out more...

You get a stress wave that travels through the metal, when it gets to the end the final bit can't pass it's energy to anything else (except the air a bit) so the molecules on that side push out a little bit and then twang back, sending the wave back through the material.

That happens hundreds or thousands of times a second depending on the structures resonant frequency.