Affect of Atmospheric Pressure


To demonstrate the effect of atmospheric pressure by making a partial vacuum by condensing steam 




Figure 1(a): A force applies to the body using a finger (b): The same force applies to the body when using needle 

In Figure 1, you are applying the same force to the body. In Figure 1(a), the force is applied by a finger, and in Figure 1(b), it is done using a needle. But the skin breaks when we use the needle. What is the reason? 

Pressure is the reason for the lasting effect of force using a needle.  


Where F is the applied force, and A is the area  

SI unit of the pressure is Pascal (Pa). 

When we apply force using a needle, the force is applied over a small area. But it is enough to break the skin. When we apply force using a finger, force is applied over a larger area than a needle. It is not enough to break the skin. In figure 1(a), the area is larger, so the pressure is low. In Figure 1(b), the area is smaller, so pressure is high. 

Figure 2: Pressure inside the tyre  

Pressure is exerted perpendicular to the surface. In Figure (2), the pressure inside the tyre exerts forces perpendicular to all surfaces it contacts. 

Atmospheric pressure 

A mixture of gases surrounds the earth due to gravity. The layers of air that surround the earth are called the atmosphere.  The earth pulls the layers of gas downward. It creates pressure on air particles. Atmospheric pressure is the force exerted by the weight of the earth's atmosphere on any given area.  

The absence of pressure is known as a vacuum. 

Air always flows from high-pressure regions to lower-pressure regions. Winds result from the pressure difference or the movement of air from areas of higher pressure to areas of lower pressure. The greater the pressure difference, the stronger the winds will be. 


A barometer is a device used to measure atmospheric pressure. It consists of a glass tube that is closed at one end and contains a non-volatile liquid. The tube is then inverted and immersed in a container of the same liquid. 

Figure (3): Barometer 

Working of the Barometer 

  • Air exerts pressure on the liquid outside of the glass tube.  
  • The pressure inside the glass tube is negligible.  
  • This pressure difference causes the liquid to rise in the glass tube.  
  • How much the liquid rises depends on the atmospheric pressure. 

In this experiment, we are creating a partial vacuum, which is an area of extremely low pressure, by heating and releasing air from the flask. 

We are observing how water rushes from sea-level atmospheric pressure to the partial vacuum. 


Learning Outcomes 

Students understand  

  • The affect of atmospheric pressure. 
  •  How fluid flows from high-pressure regions to lower-pressure regions. 
  • The working of the barometer.