Can you get a milk bottle to suck an egg in without you touching it? Kids never cease to be amazed by this little trick, no matter how many times you show it to them.
What you'll need: one hard boiled egg, peeled; boiling water; a heat-proof glass bottle with a neck slightly smaller than the egg (e.g. milk bottle).
- Set the egg on the neck of the bottle to demonstrate that the egg simply won't fit in the bottle. Tell the child that you know a trick to make that egg go down into the bottle without touching or breaking it.
- Remove the egg from the bottle and pour the boiling water into the bottle. Carefully roll the water around in the bottle and then pour it out.
- Quickly put the egg back on the neck of the bottle and wait for it to get sucked down into the bottle.
When you put the hot water into the bottle and then pour it out, the hot water leaves steam behind in the bottle. The steam forces out some of the air that was already in the bottle.
As the steam in the bottle cools down, it converts into tiny droplets of water. The drops of water require less space and this reduces the amount of air pressure in the bottle. The pressure on the outside of the bottle is greater than the pressure on the inside, and that is what forces the egg into the bottle.