Why make it so you have to slow down to a couple miles an hour to go over them when the speed limit is 20 or 30? Why not just make them lumpy enough so it's uncomfortable to be speeding?
It uses the well known reaction Acid + carbonate salt + water + carbon dioxide. The carbon dioxide will not support combustion and is heavier than air, so puts the fire out. Often a detergent type chemical is present so the CO2 forms a foam, making it more effective.
Well you don't have to heat the sand yourself! You could show a video of glassblowing if you have a projector screen - there are plenty available on YouTube! If you want to go into glass a bit more, you could research a bit about how different transition metals are used to change the colour of the glass. Sticking to your original theme, this can happen in nature too - the mineral obsidian is a natural glass and can be found in black, green, grey, red or yellow forms. I don't know how much time you have or how good it has to be, but if time allows you could maybe bring in a glass bottle/jar and show on your particular bottle how it would have been blown - it makes things more interesting for your audience if they can see it in front of them, and you could hand it round the class too. If you have any obsidian it might be really cool to show that round too and tell everyone it's a semi-precious gem - they might be interested!! If you don't have any you can often buy little pieces of obsidian from museums. I'm not sure about obsidian being created by lightning; I think it's usually by volcanoes but I presume that lightning does pretty much the same thing because it's a natural glass. It always keeps people interested if you have stuff to hand round. :) good luck xx
