Force and Laws of Motion - Class 9 PDF Download

Force

• A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. 
• When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
• Force is a quantity that is measured using the standard metric unit known as the Newton. A Newton is abbreviated by an "N." To say "10.0 N" means 10.0 Newton of force.

»Types of forces

  For simplicity sake, all forces (interactions) between objects can be placed into    two broad categories:

1. contact forces
2. forces resulting from action-at-a-distance

Contact forces are those types of forces that result when the two interacting objects are perceived to be physically contacting each other. 

Examples: Frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.

Action-at-a-distance forces are those types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. 

Examples: Gravitational forces, Magnetic forces, etc.

»Balanced and Unbalanced Forces

When balanced forces are applied to an object, there will be no net effective force acting on the object. Balanced forces do not cause a change in motion.

Unbalanced forces acting on an object change its speed and/or direction of motion. It moves in the direction of the force with the highest magnitude.Balanced and Unbalanced Forces