Teach Engineering: Let's Get Dirty

In a very hands-on activity, students observe and feel the differences between two cleaning methods, with and without hand soap, using coffee grounds to represent "dirt."Most of the dirt and bacteria on our hands is encased in a thin layer of oil, so because of the properties of oil and water, cleaning your hands with water alone has little effect when trying to remove the dirt. This activity demonstrates the importance of using a surfactant, such as hand soap, when washing your hands.