CH 6: Pressure

• Pressure, symbolized as p, is the force acting per unit area, and the formula for pressure is p equals f over a.
• Pressure is a scalar quantity, and the unit of pressure is Newton per meter square or Pascal symbolized as Pa.
• To increase the pressure, one can increase the force or reduce the area.
• Common units of pressure often include Pascal (Pa), mmHg, and Atm.
• Atmospheric pressure at sea level is represented as 1.013 times 10^5 Pascal (Pa).
• For pressure 1, it is equal to the pressure of the gas.
• The SI unit for pressure is Pascal (Pa).
• An example of increasing the pressure is a nail and a hammer, where a hammer, which is heavy, gives a great force, while a nail, with a small area, is easy to press to the bottom.
• An example of reducing the area is wearing narrow high heel shoes versus broad and low heels, which is more tiring.
• An elephant with a mass of four thousand kilograms standing on the ground with both legs exerts a total pressure of 318 thousand Pascals.
• The formula for pressure in liquid is p equals rho g h, where rho is the density of the liquid, g is the acceleration due to gravity, and h is the depth of the liquid.
• The pressure of liquid increases with the depth.
• Pascal's principle states that the change in pressure applied to an enclosed fluid is transmitted unchanged to every part of the fluid and the walls of the container.
• The pressure at piston 2 (p2) is equal to the pressure at piston 1 (p1), as they are at the same level.
• Pressure is transmitted equally to every part of the liquid, including the piston.
• Atmospheric pressure is used in drinking water using a straw when sucking the water, as the low pressure in mouth and the atmospheric pressure is higher pressure which will push the water through the straw.
• The earth is surrounded by a layer of air called atmosphere, which exerts a pressure on the surface of earth known as atmospheric pressure.
• A suction cup utilizes atmospheric pressure to hold it tightly against the wall, hence it will not drop.
• A barometer utilizes a liquid column to measure atmospheric pressure, usually mercury is used as liquid column because it has high density hence it does not create a column that is too high to measure.
• A manometer is used to measure the pressure difference between the atmospheric pressure and a gas or liquid in a container.
• If the tube of a manometer is open ended at one end, it is exposed to atmospheric pressure.
• Atmospheric pressure decreases as altitude increases as the density of the air decreases at greater heights.
• The average atmospheric pressure at sea level is 1.013 times 10^3 Pascal or 1 atmosphere (1 atm).
• The basic structure of a barometer consists of a glass tube and mercury.
• The perpendicular height that is measured in a barometer is the height of mercury.
• The area of piston 1 (a1) is greater than the area of piston 2 (a2), hence the force (f2) on piston 2 is greater than the force (f1) on piston 1.
• A syringe works in a similar way, as when the plunger is too up, there is a low pressure in the barrel so the atmospheric pressure which is higher pressure will push the liquid into the barrel.