What is Newton's First Law of Motion- [Definition,Examples, Formula]

Many a times question arises that what is Newton's first law of motion- Definition, Examples and what is its formula. Our Today discussion about the newtons first law of motion.

Let's start. Newton's laws of motion. Sir Isaac Newton (1642-1727) made a systematic study of motion and extended the ideas of Galileo. He arrived at three laws of motion which are called Newton's laws of motion. 

What is Newtons First Law of Motion?

This law consists of three parts:

1. First part says that a body at rest continues in its state of rest. An external force has to be applied on it to make it move. A chair lying on the floor will continue to remain there unless we displace it.
2. Second part says that a body in motion continues moving in a straight path with a uniform speed. This part seems to be contrary to our everyday experience. A rolling ball comes to rest on a rough ground. This is because of the force of friction. The ball moves through a larger distance on a smooth floor. If the friction were zero, the ball would continue its motion forever. This part also indicates that to increase or decrease the speed of a body moving in a straight line, a force has to be applied on it in the direction of motion or opposite to the direction of motion.
3. Third part says that a body moving with a uniform speed in a straight line cannot change itself its direction of motion. To change its direction of motion, a force has to be applied normal to this direction of motion. Consider the motion of the moon around the earth. The direction of motion of the moon continuously changes. The force needed to change the direction is provided by the gravitational attraction of the earth on the moon.

Newtons First Law Definition

Newton's 1st law of motion. This law states that everybody continues in its state of rest or of uniform motion in a straight line unless it is compelled by some external force to change that state.

Newton's First Law Defines Force - (Let's See How)

According to Newton's 1st law, a body at rest or in uniform motion will remain at rest or in uniform motion unless an external force acts upon it. This shows that Force is an agency which changes the state of rest or uniform motion. But sometimes a force applied on a body is not able to change its state of rest or of uniform motion.

So, it is better to define force as an external agency which changes or tends to the state of rest or of uniform motion in a straight line. Hence, the 1st law gives a qualitative definition of force.

Newton's First law Defines Inertia

First Read: What is  Law of Inertia?

According to Newton's 1st law, everybody continues in its state of rest or uniform motion unless an external force acts upon it. This shows that a body, by itself cannot change its state of rest or uniform motion. This inability of a body to change its state of rest or of uniform motion along a straight line is called inertia of the body. Thus, the first law defines inertia and hence it is rightly called the law of inertia.

Newton's First Law Formula

Mass of the body is the measure of the inertia. Since Newton first law is based on the concept of inertia.So, we can have the formula.

More Mass ∝ Difficult to change the state of rest or of uniform motion.

• If we kick the football.it flies a long way. If we kick a stone of sam the size, it hardly moves.
• When a moving bus stops all of a sudden. Then a passenger standing in it tends to fall in the forward direction. This is because the lower part of his body which is in contact with the bus comes to rest but the upper part of his body due to inertia of motion continues to move.

So, the material has the inherited property by virtue of which it cannot the change, by itself, its state of rest or motion in a straight line.

Newtons First Law of Motion Examples

Based on inertia of rest

• Dust is removed from a hanging carpet by beating it with a stick. As the carpet is beaten it suddenly moves forward while the dust particles tend to remain at rest due to the inertia of rest and so fall off.
• When we shake the branch of a tree, its fruits and dry leaves fall down. On shaking the branch comes into motion while the dry fruits and leaves tend to remain at rest (inertia of rest) and so get separated.

Based on inertia of motion

• A person getting out of a moving bus or train falls in the forward direction. As the man jumps out of a moving bus, his feet suddenly come to rest on touching the ground while the upper part of his body continues to move forward. That is why he falls with his head forward. In order to save himself from falling down, he should run in the forward direction through some distance.
• An athlete runs a certain distance before taking a long jump. The inertia of motion gained by him at the time of jumping adds to his muscular effort and helps him in taking a long jump.

Based on the inertia of direction

• When a dog chases a hare, the hare runs along a zig-zag path. It becomes difficult for the dog to catch the hare. This is because the dog has more mass and hence has more inertia of direction than that of the hare.
• During the sharpening of a knife, the sparks coming from the grindstone fly off tangentially to the rim of the rotating stone. This is due to the inertia of direction.

This is all about the basics of what is Newton's first law of motion, definition, Examples and what is its formula.