The students worked together with their mentors from Black & Veatch to find the difference between salt water and fresh water as drops were placed on a penny. Challenged to discover how many drops of water would fit, the students got a lesson focused on cohesion and surface tension. Cohesion is the attraction of like molecules to one another. In this case, the like molecules were the H20 molecules in the water drops. Surface tension is a special term the mentors used to describe the cohesion between water molecules. Testing both salt and fresh water, the students raced to see which group could get the most drops of water on a penny without the water overflowing.