Sometimes, we fail to notice small occurrences in our daily life that explain some basic scientific facts. For instance, have you ever noticed that you can actually hold a glass filled with water upside down, without spilling a drop of it? Yes, there will be a cover over the water, but not a tightly held cap. Let us do this upside down water experiment, and explain more.
Materials Required
Drinking glass – 1
Water – enough to fill the glass
Hard paper or cup coaster – 1
Large container or sink
Steps to follow
- Pour water in the glass to its brim.
- Rest the paper or coaster over the glass, so as to cover it.
- Lift the glass, and hold it over the large container. (This is just a precaution so that you don’t end up mopping the floor instead of learning science, just in case something goes wrong)
- Holding the paper with one hand, flip the glass over the container.
- Slowly free your hand which is holding the paper.
- Did the water fall into the container? No. It is still inside the glass, with the paper sheet magically clinging to the glass.
What we learn
What we saw was the practical application of the principle of air pressure. Air pressure refers to the pressure exerted by air over everything on earth. Air that surrounds us, in fact, is exerting pressure on us from all directions. We just don’t feel the pressure, as we are used to it right from our birth.
In our experiment, it was the upward pressure exerted by the air below the paper that prevented the water from flowing out. Though we filled the glass to the brim, a few drops of it escaped as we tilted it. If you notice the tilted glass, you can see a minute air column just over the water surface. This air column at the top (which was previously the bottom) contains very few air molecules.
The downward pressure exerted by these air molecules is lesser than the pressure exerted by the air molecules pushing from below the paper. The airtight seal between the rim of the glass and the paper prevents further air from entering the glass. If we break this seal by shaking the paper even minutely, more air enters the glass. Then air pressure inside and outside will be equalized, and water flows out due to the force of gravity.
Watch this video to see a demonstration of the experiment along with an interesting animated explanation.
Was it not an easy way to learn about air pressure? For more such fun-to-do experiments, visit our Experiments section.
