Floating Fish

This experiment looks at solubility and density.

1. Draw the outline of a fish on the bottom of a glass plate or tray in whiteboard pen/dry-erase marker. Retrace your drawing to make sure all the lines are connected. Let dry for a minute or two.
2. Fill a measuring cup with tap water. Place the pour spout just inside the corner of the dish and add water very slowly until it just covers the bottom. Be careful not to pour water directly onto your drawing or make splashes near it. The water will move toward your drawing, eventually surrounding it. Observe what happens. If the water splashes or it doesn’t work on your first try, empty the dish, erase the drawing with a paper towel, dry off the dish, and try again.
3. Tilt the dish slightly from side to side. What happens? 

The ink in whiteboard pens/dry erase markers is designed to be slippery. It’s made with a chemical that causes it to easily release from surfaces. (Permanent markers are made with a chemical that makes the ink stick to surfaces, so be sure not to use these in your experiment!)

The ink lets go from a surface, but why does it float? There are two reasons. First, the ink isn’t soluble, which means it won’t dissolve in water. Second, the ink is less dense (less heavy) than the water, so it becomes buoyant, meaning it can float. When you tilt the dish, the fish moves around on the water’s surface.