[thedoc (OP)]

Stick two glasses together using the power of hot air.

Read more about this kitchen science experiment.

Listen to the Experiment [chapter podcast=1253 track=08.11.02/Naked_Scientists_Show_08.11.02_2778.mp3","]_{Part 1}[/chapter] [chapter podcast=1253 track=08.11.02/Naked_Scientists_Show_08.11.02_2790.mp3","]_{Part 2}[/chapter] [chapter podcast=1253 track=08.11.02/Naked_Scientists_Show_08.11.02_2778.mp3][/chapter]
...or download as MP3 [1] [2]

[daveshorts]

A question from a listener...
What will happen if i replace the hot water with cold water?
What are the explanations for the result (eg, the pressure and air etc) ?

[daveshorts]

The hot water is causing the air to heat up increase in pressure and then expand, as air escapes because the glasses can be pushed apart easily and air can leak out.

 It then cools down and tries to shrink, it can't suck air in as the reduction in pressure means that the glasses are pushed together by the larger pressure outside them.

If you used cold water it would cool the air to start with causing it to shrink, then as it warms up over time it will just be able to expand and escape through the gap.

If you sealed the two glasses together when at room temperature and then cooled them, the pressure inside shoule be reduced and they may well stick until they warm up again.