value of standard atmospheric pressure
N/m2
what is used to measure compressed air?
pressure gauge
SI unit of pressure
pascal
what is used to measure atmospheric pressure?
barometer
what is used to measure liquid pressure?
Manometer
unit of compressed air
key performance indicator
what is pressure?
the force applied per unit area
define standard atmospheric pressure
the pressure exerted by the atmosphere of about 760 mm of Hg at the sea level
factors of liquid pressure
- the density of the liquid
- the depth of the liquid column
- the value of acceleration due to gravity at the place
what is the formula of liquid pressure?
dhg
what is the formula of pressure?
p=F/A
factors of pressure
the amount of force applied
surface are of a body
characteristics of liquid
1.Pressure in a liquid increases with the depth of liquid
2. a liquid finds its own level.
3. liquid transmits pressure equally in all the directions.
4. the pressure at any point in a liquid depends on its density.
relation of liquid pressure
p=w/a
w=mass x gravity
density = mass/ velocity so mass= density x velocity
velocity= area x height
a and a crosses out
left with p= dhg
applications of liquid pressure
- use din waterslides and tunnels in waterpark.
- used in hydropower plants to generate electricity.
- used to wash away dirt and sewage at dirty places.
- used in irrigation systems.
- used in submarines.
- used to measure the density of the liquid.
importance of compressed air
- for transferring energy.
- plays a fundamental role in powering our modern world.
- used for power tools such as hammers, drills, and wrenches.
- used to operate air cylinders for automation and to propel vehicles.
- used as a breathing gas by underwater divers.
What is atmosphere?
The region of air which surrounds the earth
What is a barometer?
An instrument for measuring atmospheric pressure
Who invented a barometer?
An Italian scientist, Torricelli invented a barometer at about the middle of seventh century
What is Torricellian vaccum?
The empty space above the surface of Hg in the tube
Why can’t water be used instead of mercury in a barometer?
- The density of water is less than the density of mercury.
- Water is sticky to the walls of barometer which makes it difficult to note the exact reading.
- Water vaporizes easily which gives some errors in the reading of barometer.
- Water is transparent so it is not seen clearly in the column.
Importance of atmospheric air
- Balances out the pressure in and out of our body.
- Air pumps can fill air in the tubes of vehicles, balls etc due to atmospheric pressure.
- Water pumps can pull or lift water.
- A syringe can work and ink can be filled in pens.
5: change in atmospheric pressure causes the wind to blow and it also helps to rain. - We can suck juices, cold drinks etc form their containers.
Prove the presence of atmospheric pressure.
Materials required: a glass tumbler, water and a postcard
Procedure:
1. Take a glass filled with water and cover it with a postcard.
2. Invert the glass tumbler supporting the postcard against the glass with the palm.
3. Holding the glass, remove the supporting palm slowing from the postcard.
Observation:
We find that the postcard remains attached with the tumbler and water does not fall down.
Conclusion:
It is due to pressure of the atmosphere exerted on the postcard which holds it on the place. This activity confirms that the atmosphere exerts pressure on the body from all of its sides.
Events occurred in our daily life which are directly related with pressure
- There is more pressure exerted by a girl’s pencil heel shoes than an elephant’s foot.
- Every nail has a wider head and a pointed end that makes it easily to pass it in the wall when hammered on the head.
- Buses and trucks have their rear wheels in pairs which increases the surface area that reduces pressure.
- An axe has a sharp edge that helps to cut wood by exerting more pressure due to the less area of its edge.
