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Monday, November 28, 2011

Making a shower- air pressure

Today we are going to see something we see every day but we are not trained to think about it. In fact is very simple and very easy to understand.

When we uncap a bottle and we turn i upside down, the liquid inside is spilled. But it will go slowly if you maintain the botlle at the 90 degrees angle, if you reduce the angle to 45 or even 30 degrees the flow of liquid increases . 

If it's your job to refill the cruet you know exactly what we are talking about.

What we need 

  • plastic bottle,
  • water,
  • hammer.
  • nail,
  • big bowl.
How to:
  1. Fill the bowl with water;
  2. With the hammer and the nail open 3 small holes on the bottom of the bottle, don't make them to large;
  3. Place the bottle inside de bowl;
  4. Fill the bottle with water;
  5. Close it tight;
  6. Grab the bottle by its neck and lift it, don't squeeze;
What happen? 
Nothing, water remains inside.
Slightly uncap the bottle, and now?
Close it again, and now?
We easily observe that even with a punched bottle the water stays inside, however, if we uncap the bottle the water flows.

The bottle is filled with water, but in order to make the water come out the bottle it is necessary that something "takes its place" inside the bottle.

Since the bottle is closed and the bottleneck is the only place where "something" can go in the bottle, the water stays in.
This something is the air. When we slight uncap the bottle the air goes in and push the water down, through the holes, taking its space inside the bottle.

In other words:
Atmospheric pressure.

When the cap is tight, the atmospheric pressure, which acts in all directions, apply force through the holes and secure the water inside the bottle.
If the bottle is closed, that pressure doesn’t act directly on the surface of water, the water remains inside.
If you uncap the bottle, atmospheric pressure acts in water surface and the water falls through the holes.

Et voilá!
Tricky uh?


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