another 5 year old question

[thekraut]

Please help me with this one:

Why does the hole in a metal ring gets bigger if you heat up the material, even though the metal expands? I know that it does but can not explain it to my 5 year old niece. so simple explanations would be helpful.

[Hammer]

The easiest way to demonstrate would be with a piece of play-dough. Make a ring and then pull it outwards to make the whole thing bigger. Hey presto, a bigger hole!

[PunkDaddy]

when things heat up they get bigger (expand) when they coold down they get smaller (contract) . They just do.

[Cloned]

except water, weird huh.

[Peter Pedant]

Erm, five inch piece of string - and make it into a ring. Say that the 'metal' is heated and expands and so is now a six inch piece of string (which you have previously cut and secreted in your pocket) and in making a ring, the six inch string makes a ring with a bigger hole.

(The hole has to get bigger to accommodate the expansion)

[stevie21]

I think the original question meant "why doesn't the inside of the ring expand inwards and make the hole smaller?"
If the ring was a balloon & was inflated, then it would expand outwards at the outer edge (making the circumference larger) and also inwards at the inner edge (making the hole smaller).

[Hamish]

I must have a five year olds view of the world, I've beet trying to think of an explanation for this all week! Here goes...

If the metal gets bigger then, for the hole to get smaller the metal would have to squash itself. The result is that the metal 'pushes' against itself and makes the hole larger. (note 5 yearolds version)

[incitatus]

it isnt hard.  think of the ring as a rod of length 3cm and width 0.1 cm.  say that at 50 degrees the rod material expands by 10%.  the increase in length will be 0.3 cm and the increase in width will be 0.01 cm.  so the circumference will have increased by 0.3 cm, equating to a radial increase of around 0.05 cm (0.3/2xPi)

The sideways expansion will make the ring hole smaller by 0.005cm but the lengthways expansion will make it expand by 0.05 cm giving a total increase in hole radius of 0.045cm.

[incitatus]

cloned, liquid water does expand when you heat it.  its only the transition from ice to water where it contracts.

[Bert]

Imagine the ring is not a ring, but a disc, with an (imaginary) dotted line showing your niece where the ring is.  You should have no trouble in imagining that the whole of the disc expands radially from the centre as it is heated.  So the dotted line goes further away from the centre.  Since the metal cannot "know" that it is a ring or a disc, its behaviour is the same in either case, so the internal diameter of the ring increases.

Alternatively, when a metal (or anything else) expands, the atoms move further apart in ALL directions.  If the inner diameter of the ring were to get smaller, the atoms on that surface would be getting closer together, so that cannot happen.

[Bert]

Actually, incitatus, water starts to expand as it cools down from about 4 degrees Celsius (the temperature of maximum density for water.  At the actual freezing point of water there is quite a sudden increase in volume.  This is because the crystal stucture of ice is quite open (lots of space between the water molecules, which are held in the crystal form by fairly weak hydrogen bonds).  Clearly, from about 4 degrees downwards, the water molecules start to arrange themselves pretty much as ice, though they are still mobile, so the space between the molecules starts to increase.