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
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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