Flash Science: Surface Tension and Pressure
Can a mesh fabric trap water in a glass? Sometimes! Brenna and Brian explain it all in this simple experiment!
What’s Going On?
There’s two important pieces of physics, surface tension and pressure. Water molecules have a lot of cohesion: they like to stick together. The surface of the water is attracted to the rest of the water (the bulk); this is a phenomenon known as surface tension. In order for the surface of the water to go through the mesh, it has to pull away from the rest of the water and overcome this surface tension. There is also a bubble of air trapped at the top of the inverted glass. As the water moves downward, this gas bubble expands and its pressure drops. The air pressure outside the glass holds the water up. This is similar to how by sucking on a drinking straw, you decreasing the pressure on the top of and water can move up into your mouth. Between surface tension and pressure, the mesh forms an impenetrable barrier for the water. However, if you tip the glass enough, air can start coming inside the glass which increases the pressure in the gas bubble and allows the water to flow out.