How much money will go into a glass of water? That’s the question on this moment of science.

Carefully fill a glass of water, until the surface of the water is exactly level with the brim of the glass. Now, gently drop a quarter into the glass. The water surface will bulge upwards slightly, but water won’t run over the rim of the glass. Water molecules attract each other. That attraction makes a film under tension at the surface of the water. Even though the water is bulging upwards, surface tension keeps it from spilling. Now the game is this: how much change can you drop in the water before water spills over the rim of the glass?

Every coin displaces an amount of water equal to its own volume. In other words, the bulge at the top of the water has the same volume as the coins added to the glass. The film at the surface of the bulging water, caused by an attraction of water molecules, holds the water like a bag. How much water can that bag hold before it breaks?

For fun, you could agree that the next to last person to add a coin before the water spills wins all the change in the glass. To make the game last longer, use paper clips instead of coins. As before, carefully fill the glass of water until the water surface is exactly level with the rim. How many paper clips can you drop in before the surface tension breaks and water spills over the edge? Some people may guess that about 10 paper clips will do it, but remember, a paper clip is just a piece of bent wire which displaces only a tiny volume of water. You may be able to get over 100 paper clips into the glass before the water spills.

This moment of science comes from Indiana University, with production support from the office of the provost. I’m Yael Ksander.