I have done this project before and all you do is use about one tablespoon of salt in the water. This project will only take about two to three days. It's easy and almost guaranteed to get a good grade on. Put the salt in one cup of water and the other cup has just water in it. Put them in a freezer of a 60 degree temperature for 18 hours. When you take them out, one will be colder than the other. Which one will it be? You'll have to wait and see! Good luck!