One of our last 3rd grade experiments is the Penny Water Drop Experiment. Each student receives one penny and each group of 3 get an eye dropper and a cup of water. Before they start, each student predicts how many drops will fit on the heads side of the penny. Most of the estimates are between 2-10. Then, after a quick review of how to use an eye dropper, the students are off to experience how strong water molecules are attached to one another (water cohesion). This experiment shows water's surface tension. We have discussed the molecules of solids, liquids, and gases and this experiment really shows the students how strong those molecules are!