Chapter 2 Forces and Motion

2.3 Understanding Inertia

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2.3 Understanding Inertia

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2.3 Understanding Inertia

The situations show that our body has an inbuilt resistance to any change in its state of rest or motion. This reluctance to change is called inertia.

If an object is at rest, it tends to stay in that position unless some force puts that object into motion. If an object is moving, 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.

2.3 Understanding Inertia

The inertia of an object is the tendency of the object to remain at rest or, if moving, to continue its uniform motion in a straight line. The concept of inertia was explained by Sir Isaac Newton in the first law of motion.

2.3 Understanding Inertia

Newton’s first law of motion states that every object will continue in its state if uniform velocity or at rest unless it is acted by an external force.

2.3 Understanding Inertia

2.3 Understanding Inertia

2.3 Understanding InertiaRelationship between mass and inertia

2.3 Understanding InertiaRelationship between mass and inertia

If they are given a push, which one of them will be more difficult to be moved?

When both swings are set in motion, which one of them will be more difficult to stop?

2.3 Understanding InertiaRelationship between mass and inertia

The larger the mass, the larger its inertia.

2.3 Understanding InertiaEffects of inertia (Positive)

In order to pour out the chili source, 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 sauces continue in its state of motion due to the effect of its inertia.

2.3 Understanding InertiaEffects of inertia (Positive)

Droplets of water on a wet umbrella are spun off when the umbrella is rotated and stopped suddenly. The droplets of water initially move with the rotating umbrella. The inertia of the droplets of water causes them to continue moving even when the umbrella has stopped spinning.

2.3 Understanding InertiaEffects of inertia (Negative)

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

2.3 Understanding InertiaEffects of inertia (Negative)

If the car crashes while travelling, the inertia of the passengers causes them to continue in motion. This is a dangerous situation. Upon impact the passengers will crash into parts of the car immediately in front of them and suffer injuries.

2.3 Understanding InertiaEffects of inertia (Negative)

Ways to reduce the negative effects of inertia. (a)Wearing safety belts when driving. (b)An air begs is fitted inside the steering

wheel. It provides a cushion to prevent the driver from hitting the steering wheel or dashboard during a collision.

(c)The oil tank of an oil tanker lorry is usually divided into a few smaller compartments so that the effects of inertia can be reduced.

2.3 Understanding InertiaTry this!

A train in motion is more difficult to stop compare with a car because

(a)the friction of the rail way is lower than the tar road.

(b) the inertia of the train is very big compare with the car.

(c) a train normally moves with a higher speed compare with a car.

2.3 Understanding Inertia

Go home and try this!On a table are two eggs, one raw and one

hard-boiled. How can the two eggs be distinguished?