Materials You’ll Need Water colored with food coloring Two plastic cups, one smaller and a little shorter than the other (One should fit into the other, with a space between the walls.) Exploration Fill the larger cup about 1/3 full with the colored water. Set the smaller cup into the larger one, pushing it down to the bottom. Describe the change in the liquid level in the larger cup. Now, with the smaller cup still in the larger one, fill the outer cup so that the space between the two is filled almost to the top of the inner cup. As you tip the cups as though to pour the water out, tip the inner cup forward just enough so that it touches the outer one, and you’ll see that the water flows only into the inner cup.