Laws of Motion

Types of Inertia:

• Inertia of rest

• Inertia of motion

• Inertia of direction of motion

The

resistance of a body to

change its state of rest is

called inertia of rest.

Inertia of Rest:

The

resistance of a body to

change its state of motion is

called inertia of motion.

Inertia of Motion:

The resistance of a body to

change its state of direction of motion is

called inertia of direction.

Inertia of direction of motion:

Every body continues to be in its
state of rest or the state of uniform motion
along a straight line
unless,
it is acted upon by some external force.

​Newton's First Law:

Like parallel forces:
Two or more forces of

equal or unequal magnitude acting along the same direction, parallel to each other called like parallel forces.

​Types of forces:

Unlike parallel forces:
Two or more forces of

equal or unequal magnitude acting along opposite direction, parallel to each other called unlike parallel forces.

​Types of forces:

The combined effect of the multiple forces is termed as ‘resultant force’

Parallel forces are acting in the same direction:

Fnet = F1 + F2

Parallel unequal forces are acting in opposite directions:

Fnet = F1 – F2 (if F1 > F2)

Fnet = F2 – F1 (if F2 > F1)

Fnet is directed along the greater force.

Parallel equal forces are acting in opposite directions in the same line of action (F1 = F2)

Fnet = 0 since (F1 = F2)

​Resultant Force:

The rotating or turning effect of a force about a fixed point or fixed axis is called moment of the force or torque (τ).

It is measured by the product

of the force (F) and the perpendicular distance (d) between the fixed point or the fixed axis and the line of action of the force.

τ = F × d
Unit: Nm

Moment of the force: