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# Tag Archives: Liquid

## Air and Liquid Pressure

Does air pressure in a capped bottle is different as that of open bottle??

If not and the atmospheric pressure in a closed container is same as that of the surroundings let 1bar at sea level, if i consider a
tube both end open and dip one end in water (like pipette in chemistry lab) and close the other by thumb, water remain
hanged in the tube..  if we say it is because the atmosphere that pushes up on the water in the tube is same as that of remaining air in tube pushing down on the water..won’t the water fall out due to its own weight as the upward and downward pressure is balanced…

Please explain the whole process and compare weight of water with up and down pressure by atmosphere..

Again would liquid ‘ll flow out of a container through a hole in vacuum??

The Air Pressure in an open bottle is equal to the atmospheric pressure. The pressure inside a closed bottle can be different.

In the experiment described, when the tube is partially filled and the upper end is closed, the water tries to fall down creating a lower pressure above it inside the tube. This creates a pressure difference, the outside pressure greater than the pressure inside and the water can fall only upto the level where the weight of water column is balanced by the force due to difference in pressure created.
See one live demonstrations here

• A guide into hydraulics – Part 1

## How is the surface tension direction found out?

Can you, sir, explain point 44 of the attached image on surface tension.

Here’s the link in case attachment doesn’t work:
http://www.sakshieducation.com/EAMCET/QR/Physics/Jr%20Phy/12Surface%20tension%20_198-208_.pdf

How is the surface tension direction found out?
{i know it tangential but in which direction along the tangent?}
Also why is surface tension for Solid-Air Surface considered when balancing forces on liquid?

Answer: Surface tension acts tangential to the surface of a liquid. If we imagine a line on the free surface of a liquid, the force of surface tension acts perpendicular to this line and tangential to the surface.

At a solid liquid interface the forces of cohesion and adhesion come to play.

In the diagram, T does not necessarily represent Surface Tension. Please remember that surface tension is the property of a liquid at surface.

Here T2 and T3 stand for the force at the point of contact along the solid surface. Further discussions are welcomed.

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