Force and pressure Class 8 Notes For CBSE Board - Textbook simplified in Videos

Force: Push or pull on an object
Magnitude and direction of force:
- If forces have same direction then magnitude of resultant force will be higher
- If the forces have opposite direction the magnitude of resultant force is lower
- Equal and opposite forces cancel out and so the resultant force becomes zero
Force results in change in state of motion and / or change in shape of object
Speed: Distance covered divided by time
Contact forces: A force that can act with being in contact with object. E.g muscular force, friction force, etc.
Non contact forces: Forces that act without in contact of the object. E.g. magnetic force, electrostatic force, gravitational force, etc.

Force	Definition	Type (Contact / Non contact)	Examples
Muscular force	It is the force due to the action of muscles	Contact force	Hitting the iron nail, kicking the football, etc
Magnetic force	Force due to attraction or repulsion of the poles of magnet.	Non contact force	Attraction of iron filings towards a magnet.
Force of friction	Acts in a direction opposite to the applied force.	Contact force	Ball rolling on the ground stops after a while
Electrostatic force	Force of attraction or repulsion due to non moving charges present in the body.	Non contact force	Bits of paper gets attracted towards the comb when comb is rubbed on cats fur.
Gravitational force	Force of attraction between any two objects in the universe	Non contact force	Stone when thrown up in the air falls back on the ground surface

Pressure: Force per unit area applied on the body.
Formula: P (Pressure) = F (Force) / A (Area)
Pressure is exerted by solid, liquids as well as gases. For example
- Iron nail with sharp end can be easily pinned into the wall.
- Water from the bottom hole of a bottle falls farther than water from the upper hole of the bottle.
- Tyre of cycle burst due to pressure exerted by air.
Atmospheric pressure: Pressure exerted by air in the earth’s atmosphere.

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