Surface tension
Tip the container backwards and forwards – what happens? You are experimenting with the surface tension of the water, one of several properties that make water a really cool liquid.
The water container is divided by a sheet full of little holes. If you flip the container quickly, you can get the water to stay in the top part of the container despite all the holes. The surface tension of the water and the air pressure means that the water stays put without leaking. When all the holes are covered by water, no air can get into the upper part and the water is kept in place by the negative pressure.
The surface tension in water is created by the forces acting between the water molecules and the air molecules. Water is positively charged, which makes the water molecules stick together. The charge means that the water molecules do not want to get in contact with the air molecules. This creates an inward force which leads to a slightly curved surface. If you want another example of surface tension, you can pour water into a glass to the point where it almost spills over and the surface will look convex.
Other experiments that show you surface tension in a cool way are the Bell Fountain and the Colliding Water Jets.
You can also keep experimenting at home:
This is what you need:
- A glass
- Paper
- Water
How it’s done:
- Fill the glass with water.
- Cover the top of the glass with the paper.
- Hold the paper in place and turn the glass upside down.
- Carefully remove the hand holding the paper in place.
Tips:
- You can use a regular drinking glass and writing paper.
- Try making a hole in the paper and see if the experiment still works!
