Page 1 - LN-Introduction to force

SAI INTERNTIONAL SCHOOL
Class 8
Lesson Notes
Subject- Physics
Ch- Force and Pressure
Subtopic- Introduction to Force

DEFINITION OF FORCE:
Push or pull acting on an object is defined as force.
SI unit of Force: N (newton)
Other unit: KgWt (kilogram weight)
1 KgWt = 9.8 N

Newton (N):
1 Newton = Force required to accelerate a mass of 1 kg by 1 m/s².
1 N = 1 kg × 1 m/s²

Force = mass x acceleration = m x a
Gravitational force (weight) = mass x acceleration due to gravity = m x g

Object moves when force is applied to it.
• Eg : Pushing a table to move, closing the door, opening a drawer, lifting
a book.
Object at rest will not move unless force is applied to it.
Interaction between bodies is necessary for the force to come into
action. Interaction can be by direct or indirect contact (pushing a door)
between bodies or from a distance (magnet pulling in iron nail towards itself).
Force is a vector quantity:
Force is a vector quantity because it is described by both direction and
magnitude.
The strength of force is given by magnitude of force.

Eg. Force applied on the rock is 15 N towards east.
The strength of force is 15 N. The direction of force is towards east direction.

{Note: the one who applies force is agent and the one on which force is
applied is object}

Agent: Man
Object: Box