Adiabatic expansion - the Lynx Effect??

Why do aerosol body sprays feel cold? It's to do with the First Law of Thermodynamics. Temperature and heat are not the same thing. Temperature is a measure of the internal energy of the molecules - oh go on - let's call it how much they wobble. There are two ways to make them wobble more - hit them or heat them. So heat is energy that goes in to make them wobble more. We can hammer them to make them wobble more - that's called doing mechanical work. Now when the aerosol spray comes out of the nozzle it expands and thus does work on the air around it. The energy for that expansion and work has to come from somewhere. It happens so fast that there is no time for thermal energy to flow into the spray. We use the word ADIABATIC for that case when there is no time to get the thermal energy in and all the changes are wrought by mechanical work. So the molecules steal internal energy from the molecules in the spray to give the energy for the expansion. This means that there is less internal energy and the temperature has gone down. The spray feels colder.