Gravitation

06 Pressure and Thrust

PRESSURE

  • Pressure is the force acting on a unit area of the object.
  • The weight of a body is also a force.
  • It always acts in the downward direction.
  • Pressure is the force acting perpendicularly on a unit area of the object.
Pressure = ForceArea
  • The SI unit of measuring pressure is ‘newtons per square metre’ (N/m2 or N m-2) which is also called Pascal (Pa).

                                       

 1 Pa = 1 N/m2

 

  • A balloon becomes harder to blow as it becomes bigger and bigger.
  • This is because the air pressure inside the balloon increases.
  • In fluids, pressure always acts perpendicular to the surface of an object and forms the thrust force on an object submerged in water.
  • Pressure applied by the fluid is:
Pressure = ThrustArea

THRUST

  • An object submerged in water appears to weigh less.
  • Similarly when a person swims, he feels as if his weight has reduced.
  • This is because the fluid applies an upward force on the submerged body.
  • This force is known as thrust and acts opposite to gravity.
  • So, total weight of the body reduces.
  • The force acting on a body perpendicular to its surface is called thrust.
  • Thrust per unit area is called pressure. Thrust is represented as:
Pressure = ThrustArea
  • The same force produces less pressure if it acts on a large area but it can produce high pressure if it acts on a small area.

Everyday Scenarios On The Basis Of Pressure:

The same force produces less pressure if it acts on a large area but it can produce high pressure if it acts on a small area.

 

 

Scenario 1: Sharp Knife Cuts Better than a Blunt Knife

Due to the thin edge of the sharp knife, the force of our hand falls over a very small area of the object producing a large pressure. And this large pressure cuts the object easily.

 

 

Scenario 2: School Bags have Wide Straps.

A school bag has wide strap made of thick cloth (canvas) so that the weight of bag may fall over a large area of the shoulder of the child producing less pressure on the shoulder. And due to less pressure, it is more comfortable to carry the heavy school bag.

 

 

Scenario 3: The tractors have broad tyres

The tractors have broader tyres so that there is less pressure on the ground and the tyres do not sink into comparatively soft ground in the fields.

 

 

Scenario 4: Wooden sleepers (or concrete sleepers) below railway lines

Wooden sleepers are kept below the railway line so that there is less pressure of the train on the ground and railway line may not sink into the ground.

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