Class 8 Force And Pressure Notes

Class 8 Force And Pressure Notes

Force :

A push or pull on an object is called force.

  • S.I Unit = Newton

Effects of Force :-

Change in state of motion :-

  • Change in the speed of an object.
  • Change in its direction of motion.

Change in shape and size of an object :-

  • We can change shape and size of an object by compressing, stretching and bending the object.

Types of Force :-

Contact Force :-

The type of force that came into action when two bodies or object are in physically contact with each other.

(1) Muscular Force :-

The force resulting due to the action of muscles is known as the muscular force.
Ex :-  Lifting a heavy box, pulling a bucket of water, pedalling a cycle.

(2) Friction :-

The force that opposes the relative motion between two surfaces is known as Frictional force.

  • Acts between the surface of the two bodies in contact.

Non-Contact Force :-

The type of force that do not need contact for action is known as Non-contact force.

(1) Magnetic Force :-

A magnet exert force on another magnet or magnetic material without being in contact with it. the force, exerted in this case, is known as magnetic force.
Ex :- Force between Magnet and iron.

(2) Gravitational Force :-

The attractive force that pulls objects towards the center of earth is called gravitation force.

  • Property of the universe, every object attracts or exerts a force on every other object.

(3) Electrostatic Force :-

The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.

Pressure :-

The force acting on a unit area of a surface is called pressure.

  • Pressure = Force / Area
  • S.I Unit = Pascal

Pressure Exerted by Liquids and Gases :-

  • It is the force exerted by liquids or gases per unit area.
  • Liquids and gases exert pressure in all directions. The pressure inside a them increase with depth.
  • Liquid pressure, on the bottom of the container (due to weight of liquid column), does not depend on the area of the bottom.
  • Liquid pressure at any point inside the liquid, depends upon the density of the liquid and the height of liquid column above the point.

Atmospheric Pressure :-

The air present in atmosphere exerts a pressure on the earth which is called atmospheric pressure.

  • The value of atmospheric pressure at the sea level is 101325 Pascal.
  • The atmospheric pressure keeps on increasing as we move towards the Earth’s surface.
  • Atmospheric pressure exists in all directions. The instrument used for the measurement of atmospheric pressure is known as a barometer.


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