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Pressure for Class 8 CBSE

Let’s start with the topic Pressure for Class 8 CBSE. In my previous post I discussed on Force for Class 8 CBSE. If you miss out please read that first. It will helped you to understand this topic. So without wasting the time start to clear some basic questions.

What is pressure?

As per definition of Pressure for Class 8 CBSE syllabus,It is defined as the force per unit area.

The SI unit of pressure is pascal (Pa), which is Newton per square metre.

Pressure (in Pa) = Force (in Newton) / Area (in meter2 )  [P = F/a]

Is it clear to us? Let’s do some simple mathematics to clear the definition of pressure.

If a force of 2 N is applied over an area of 2 cm2, calculate the pressure produced.

Sol.

To get the pressure in Pa, we have to make sure that the force is in Newton and the area in m2.
Here, the area is in cm2. To convert this to m2, we have to divide the given area by 10,000
Thus, area = 2 / 10000 = 0.0002 m2
Now, Pressure = Force / Area = 2N / 0.0002 m2 = 10,000 Pa
Now we have to look some important property of pressure.

VARIATION OF PRESSURE WITH AREA

The same force, increasing the area over which it acts decreases the pressure applied. The inverse is also true that decreasing the area of application increases the pressure produced for the same force.

  • Look at some example the area under the edge of a knife’s blade is extremely small. Beneath it the pressure is high enough for the blade to push easily through the material that needs to be cut.
  • Wall foundations have a large horizontal area. This reduces the pressure underneath so that the walls do not sink further into the ground under the weight of the building

FLUID PRESSURE

Pressure for Class 8 CBSELiquids and gases are together called fluids because they can easily flow from one place to another. Fluids exert pressure on all bodies immersed in them and on the walls of the container that holds them. The air inside the balloon exerts a pressure on the inner walls of the balloon.

 

ATMOSPHERIC PRESSURE

From the syllabus of pressure for class 8 CBSE, A layer of air called the atmosphere surrounds the earth. As we know, air is also matter and has weight. The weight of the atmosphere exerts a pressure on the surface of earth. This pressure is called atmospheric pressure. Its magnitude is around 100 kilo pascals (100 kPa) at sea level. However, as we go upward, the magnitude of atmospheric pressure decreases gradually. The following activity will show the magnitude of atmospheric pressure on the earth’s surface.

THE MAGNITUDE OF ATMOSPHERIC PRESSURE

Take a glass tumbler and fill it with water to the brim. Cover it with a thick sheet of paper (or cardboard). Press your palm over the sheet and quickly invert the tumbler. Slowly remove your palm supporting the piece of paper. What do you observe? Surprised?

Pressure for Class 8 CBSE
Pressure for Class 8 CBSE

You have seen that the paper did not fall (as one expected it to.) This is because the atmospheric pressure provides enough force to push the piece of paper upward.

LIQUID PRESSURE

As per Pressure for Class 8 CBSE syllabus, a liquid exerts pressure on the wall of the container.

Take some discarded plastic bottle and fix a glass tube near its bottom. It can be done by slightly heating one end of the glass tube and then inserting it near the bottom of the bottle. In case there is some leakage, you must seal it with molten wax. Now cover the free end of the glass tube with a thin rubber sheet. On filling the plastic bottle up to half with water, the rubber sheet fixed to the glass tube bulges. When more water is added in the plastic bottle, there is change in the bulge of the rubber sheet. Since the rubber sheet is fixed on the side of the container, it shows that water exerts pressure on the side of the container. In other words, liquids exert pressure on the walls of the container.

APPLICATIONS OF PRESSURE

(a) Drinking straw

Pressure for Class 8 CBSEDrinking straw is used to suck up aerated water, when air is sucked in, it causes a decrease in air pressure inside the straw. The outside atmospheric pressure forces the liquid inside the straw. The dropper also works on the same principle. This type of mechanism mainly known as suction mechanism.

(b) Syringe

In Syringe the pressure of the liquid (blood) force the liquid to move into the syringe when its plunger is withdrawn.

(c) Vacuum cleaner

A Vacuum cleaner is an electrical appliance that cleans by suction. A fan inside the vacuum cleaner lower the air pressure and creates a low pressure the device. As a result, the air and dirt particles on and near the surface sucked into the device.

 

Let see how you learn Pressure for Class 8 CBSE ?

Pressure for Class 8 CBSE

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