For this simple experiment you need a coin, water and a glass.
Place the coin under the empty glass. It is easy to see the coin. Now add water to the glass and the coin disappears! This is due to light refraction. Light rays travel through air with very little refraction so it’s easy to see the coin. But when light rays have to travel through water, there is much more refraction (due to molecules being much closer together in water than in air). The kids were totally amazed! Isn’t science cool?
ages 3 – 8