For School we have been talking about the Moon, which lead to questions about Gravity and the earth and so we have taken a quick detour from the planed expansion to learning about the solar system to studying the earth's make up a bit more.
Two of the ways we did this was with the classic Sodium Bicarbonate and vinegar volcano and to make pie.
I was leery of the volcano because other than being fun I did not see how it would really teach much about actual volcano or geyser explosions. But we did ours in an old drink bottle, this allowed me to talk about and demonstrate how pressers from heat and reactions below the earth crust would build up and the magma or hot water would move upward to try to escape in the same way that the pressure from the chemical reaction in the bottom of the bottle made it move up the bottle and over flow from even a small amount of the two chemicals. So it was a great way to show the energies role in the explosions and not simply a matter of volume overflow.