Laws of Motion

​Inertia:
The inherent property of a body
to resist any change
in its state o f rest or the state of uniform motion,
unless it is influenced upon

by an external unbalanced force, is known as ‘inertia’.

Inertia depends on mass of the object.

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:

Multiple Choice

When a moving bus comes to a stop, passengers feel a jerk.

This is the consequence of ____

• Inertia of motion

• Inertia of rest

• Inertia of direction

Multiple Choice

Inertia depends on ______

• Velocity

• Speed

• Distance

• Mass

Multiple Choice

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by a(n) ____________________.

• unbalanced force

• inertia

• mass

• balanced force

Multiple Choice

Seat belt is needed for safety purpose in a vehicle. What is the use of the seat belt?

• To increase the effect of inertia

• To reduce the effect of inertia

• To increase the effect of momentum

• To decrease the effect of momentum

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:

Multiple Choice

In a tug of war the left team pulls with a force of 200N. The right team pulls with a force of 150N.What is the resultant force?

• 50N to the left.
• 350N to the left.
• 350N to the right.
• 50N to the right.

Multiple Choice

What is the resultant force?

• 40 N, Left

• 0 N, Balanced

• 400 N, Right

• 40 N, Right

Multiple Choice

What is the resultant force?

• 400 N, Up

• 400 N, Down

• 800 N, Up

• 800 N, Down

Multiple Choice

How will this object move? 

• It won't move. 
• It will move to the right. 
• It will move to the left. 
• It will move in both directions. 

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:

Multiple Choice

What is the Unit for Torque

• Nm

• N

• W

• J

Multiple Choice

The easiest way to open a heavy door  is by applying the force

• Near the hinges
• In the middle of the door
• At the edge of the door far from the hinges
• At the top of the door

Multiple Choice

Find the magnitude of the torque produced by a 5.0 N force applied to a door at a perpendicular distance of 65 cm from the hinge.

• 75 Nm
• 3.25 Nm
• 6.3 Nm
• 8.75 Nm