CBSE Class 9 Answered

give examples of newtons first law of motion second law of motiom and third law of motion

Asked by disha2.bhardwaj | 29 Jun, 2015, 01:08: PM

Expert Answer

Newtons first law of motion:

A body remains at rest or in motion in a straight line with uniform speed, unless it is acted upon by an external force. Thus, all objects resist the change in their state of motion. This resistance is known as the inertia of the body.

Examples of inertia:

1. If the driver applies brakes suddenly when we are seated in a car, then we get a push in the forward direction. This is because we were in motion and inertia tends to oppose the change in our state of motion.

2. When we get off a moving bus or train, we continue to move for a certain distance.

Newtons second law of motion:

The rate of change of momentum of a body is directly proportional to the applied force and occurs in the direction in which the force acts.

begin mathsize 12px style Force proportional to fraction numerator Change space of space momentum over denominator Time space taken end fraction end style

Examples:

1. Catching a cricket ball: When a fielder catches a cricket ball, he drags his hands backwards in order to increase the time taken by the ball to reduce its momentum to zero. This reduces the rate of change of momentum, thereby decreasing the force exerted on the hands by the ball.

2. Seat belts in a car: When brakes are suddenly applied or a car crashes with an object, the seat belts increase the time taken to move forward, thereby decreasing the rate of change of momentum. Thus, the force of impact is reduced and fatal accidents can be prevented.

3. Athletes lands on sand: When an athlete lands from a height on a hard floor, he may hurt his feet because his feet comes to rest instantenously. So, a very large force is exerted by the floor on his feet. On the other hand, when he lands on sand, his feet pushes the sand for some distance, therefore the time duration in which his feet comes to rest increases. Thus, the force exerted on his feet decreases and he is saved from getting hurt.

Newtons third law of motion:

To every action, there is an equal and opposite reaction.

Examples:

1. Recoil of a pistol: When a person fires a gun, he gets a push in the backward direction.

2. Swimming: While swimming, a person pushes against the water. The water exerts an equal and opposite force on the person enabling forward movement.

3. Motion of a boat in water: To move a boat ahead in water, the boatman pushes (action) the water backwards with his oar. In response, water exerts an equal and opposite force (reaction) in the forward direction on the boat due to which the boat moves ahead.

Answered by Faiza Lambe | 29 Jun, 2015, 01:59: PM