So today i noticed a little hole in the cap of my coffee mug.
If you cover that hole, the coffee does not flow, although there is nothing holding it back.
That is, because there is something invisible called air that is pressing it back into the cup, if it can not get other air through that little hole from outside?
Which is something that constantly confuses me (or my brain), because there is nothing there.
What would be a good illustration or an imagination, how all those pressure from around us works?
In: Physics
Ever go swimming and dive underwater? What happens as you go deeper and deeper? Do you feel the pressure? Thats because as you go deeper there’s more water above you, pushing down on you, creating more pressure. Now, on land, you have a bunch of air above you. Air is a lot lighter than water, but there is literally miles of air above you, pushing down on you. Thats air pressure, and its about 14.7 lbs of force per square inch, unless your really high up like on a mountain, then its less. Once you get up and over the air, the pressure goes to essentially 0 and thats space.
That little hole in the coffee mug allows air in which is required when you pour coffee out of the mug. Without letting air in, you’re creating a vacuum which locks in the coffee and prevents it from free flowing out.
The same thing happens when you block the top of a straw that is half submerged in a cup of water and lift the straw. The vacuum created at the top of the straw by your lip or finger prevents the water from dripping out of the straw.
The air around us is pushing on pretty much everything. It’s this perpetual squeezing force that’s pushing with about 14.696 pounds on every square inch of everything. For a demo, take a syringe. Push the plunger all of the way in, and plug the end with your finger. Now, the inside of the syringe contains enough air to apply 14.696 pounds per square inch (psi). If you pull the plunger out some while keeping the end of the syringe plugged, you’re allowing the air inside to expand and lose some of its pressure. Now, the air on the outside is still pushing in at 14.696 psi, but the air on the inside may be pushing out at closer to 4 psi. If your syringe has a bore (the footprint of the plunger, you could say) of half of a square inch, then that’s two pounds being pushed by the inside air, and 7.4 pounds by the outside air. Clearly, the outside air is pushing harder. You can feel it pushing the plunger back in, in this case with a force of 3.4 pounds.
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