Atmospheric pressure is the air all around us. It weighs on us all the time, but we can’t feel it. First the atmospheric pressure (or the tiny air molecules all around us) presses against the bottom of the cardboard same way it presses against us. This pressure holds the card up. But the weight of the water should still be heavy enough to push it off right? That’s what most people would think, but if you look at the top of your upside down glass, you can see a small pocket of air. Now, the air outside the glass is at one pressure and the air inside the glass is at another. There isn’t much of an opportunity for the outside air to get into that space and equalise the pressure so what we’ve created is a small pocket of low pressure (a vacuum) inside the glass. There’s more air pushing up against the bottom of the card which creates a higher pressure area compared with the lower pressure air inside the glass. The force from the atmospheric pressure (outside the glass) holds the card up and the vacuum (in the glass) keeps the water’s weight from pushing the card down.
Well done everyone! Next this week’s experiment won’t be as challenging to understand 🤪
