INERTIA

OBJECTIVES

• To analyse the relationship between inertia and mass.

• To understand the effects of inertia in daily life experience.

• The inertia of an object is the tendency of the object to remain at rest or, if moving, to continue its motion

What is Inertia?

INERTIA makes the moving object continue to move at a constant speed in the same direction unless some external force changes the object’s motion

If the object is moving….

It tends to stay in that position unless some force puts that object into motion

If an object is at rest…

Inertia is not physical quantity and thus it does not have units

The property of inertia is found from the Newton’s first law of motion

Newton’s First Law of Motionstate that:

"Every object continues in its state of rest or of uniform motion unless it is acted upon by an external force"

RELATIONSHIP BETWEEN INERTIA

AND MASS

• Constant wherever it is measured

• Base quantity• Scalar quantity• The SI unit of mass is

kilogram (kg)

Mass can influence the

inertia

MASS INCREASES

INERTIA INCREASES

An object with a larger mass has a

larger inertia.

SITUATIONS INVOLVING INERTIA

• When the cardboard is pulled away quickly, the coin drops straight into the glass.

• The inertia of the coin maintains its state at rest. The coin falls into the glass due to gravity.

Chilli sauce in the bottle can be easily poured out if the bottle is moved down fast with a sudden stop. The sauce inside the bottle moves together with the bottle. When the bottle stops suddenly, the sauce continue in its state of motion due to the effect of its inertia.

• Body moves forward when the car stops suddenly

• The passengers were in a state of motion when the car was moving. When the car stopped suddenly, the inertia in the passengers made them maintain their state of motion. Thus when the car stop, the passengers moved forward.

Ways to reduce the negative

effects of inertia

Safety in a car: •(a) Safety belt secure the driver to their seats. When the car stops suddenly, the seat belt provides the external force that prevents the driver from being thrown forward. •(b) Headrest to prevent injuries to the neck during rear-end collisions. The inertia of the head tends to keep in its state of rest when the body is moved suddenly. •(c) An air bag is fitted inside the steering wheel. It provides a cushion to prevent the driver from hitting the steering wheel or dashboard during a collision.

• Furniture carried by a lorry normally are tied up together by string. When the lorry starts to move suddenly, the furniture are more difficult to fall off due to their inertia because their combined mass has increased.