(i) Any external imbalance that changes or tends to change the state of rest or uniform motion in a straight line or the direction of motion is called as Force.
Force always produces acceleration in the body.
(ii) Inertia is the ability of the body to change the state of rest or uniform motion, unless acted upon by an external force.
Inertia is categorized into three types:
i) Inertia of rest,
ii) Inertia of motion, and
iii) Inertia of direction.
Inertia of rest: It is the property of body by virtue of which it cannot change the state of rest by itself.
Inertia of motion: It is the tendency of the body to remain in the state of uniform motion in a straight line.
Inertia of direction: It is the property of body by virtue of which it cannot change the direction of motion by itself.
(iii) Momentum is a measure of the quantity of motion contained in the body and is equal to the product of mass and velocity.
Momentum is a vector quantity and it's direction is same as that of velocity.
Mathematically, momentum is given by,