One Way Surface Tension
Do you think you can stop water from falling from a glass held upside down with only a porous net used to hold potatoes in a grocery store? Yes friends, it is possible to stop water from falling from a glass just by using a plastic screen -if you’re utilizing the property of surface tension.
Surface tension is a property of the surface of a liquid that causes it to behave like an elastic sheet. This is what allows insects, such as the water strider, to walk on water. It allows small objects, even metal ones such as needles, razor blades, or foil fragments, to float on the surface of water, and it is the cause of capillary action. An everyday observation of surface tension is the formation of water droplets on various surfaces.
So let us do try something to see how surface tension prevents the water from falling from that net!
Here’s what materials are required:
A glass bottle with a wide mouth
Water (of course)
Aplastic mesh bag used for produce at the grocery store
A rubber band
An index card
A bowl or a bucket to catch the falling water (just in case)
First cut the mesh bag to an appropriate size, which covers the mouth of the bottle completely. Now, stretch the rubber band to seal the mesh on the mouth of the jar. Fill the bottle with water by pouring the water through the screen. This proves that the water easily flows through the screen. Fill the bottle almost to the very top.
Cover the bottle mouth slowly with an index card, so that the entire mouth is covered. Hold the card right in its place and gradually turn the bottle upside down. Bring the bottle over a bucket, just in case the water spills. Slowly remove the card from the opening, and the water mysteriously stays in the bottle!
If you have a very steady hand, try this: while the bottle is turned upside down and the water is defying gravity, gently feed a toothpick through one of the screen holes without breaking the water seal and watch it float to the surface.
The water drops do not fall from the bottle because of the intermolecular attractive force called cohesion, which is the cause of surface tension. The surface tension membrane is always trying to contract, which explains why falling droplets of water are spherical, or ball-shaped. The water stays in the bottle even though the card is removed because the molecules of water are joined together to form a thin membrane between each opening in the screen.
Pretty cool!
