Newton First law of Motion: Inertia, Concept of force...

INTRODUCTION OF FIRST LAW OF MOTION

In the seventeenth century, Sir Isaac Newton published three laws. An introduction to an object’s motion and the forces acting on it can be found in Newton’s first law of motion. Put differently, it addresses how an object moves and how force affects it. Let’s study in-depth about Newton’s first law of motion in this post.

FIRST LAW OF MOTION

Newton’s First Law of Motion states that, If no external force is applied, a stationary object will remain stationary forever and a moving object will forever move along a straight line with constant momentum, i.e. the object will not experience any acceleration.

We learn two things from Newton’s First Law of Motion – 1. Inertia of Matter & 2. Concept of Force

INERTIA OF MATTER

From the discussion of the first law, we see that the natural property of a stationary and moving object is to maintain its motion. A stationary object cannot move on its own and a moving object cannot stop on its own. In both cases matter is incapable of changing its state by itself. This inability of matter is inertia. This is why Newton’s first law of motion is called the law of inertia. The inertia of a substance is related to its mass—the more mass a substance has, the greater its inertia.

Definition: The property of matter by which an object in a fixed or moving state tries to maintain its fixed or moving state is called Inertia.

Inertia of matter is of two types – 1. Inertia of rest & 2. Inertia of motion

INERTIA OF REST

Definition: The tendency of a stationary object to remain stationary forever is called Inertia of Rest.

EXAMPLES OF INERTIA OF REST

When a car starts moving suddenly, the passengers lean backwards. When the car is stationary, the body of the passenger is also stationary. As soon as the car starts to move, his lower body moves so that it is adjacent to the car; The upper part then tries to remain stationary. As a result, the passenger leans backwards i.e. in the opposite direction of the vehicle.
If a book is quickly pulled from the middle of a stack of books arranged from the bottom up, the upper books fall, but do not break. Due to inertia of rest the upper books cannot move sideways.

INERTIA OF MOTION

Definition: The tendency of an object in motion to maintain its state of motion along a straight line is called Inertia of Motion.

2. EXAMPLES OF INERTIA OF MOTION

When a moving car suddenly stops, the passengers lean forward. When the car is moving, the entire body of the rider is in motion with the car. As soon as the vehicle stops, the rider’s lower body comes to rest but due to inertia of motion, the upper body wants to move forward. As a result, the rider leans forward.

When a passenger throws a ball straight up under the grip of a moving train, the ball returns to his hand after a while, even though the passenger moves forward a little. Due to inertia of motion the ball maintains forward motion. As a result, the ball and the passenger travel the same distance forward at the same time. So, the ball falls into the hand of the passenger. If there was no inertia of motion, the ball would fall back.
Even when an electric fan is switched off, the fan does not stop immediately. The inertia of motion allows the fan to spin a little longer—until the friction of the parts and the resistance of the outside air bring the fan to a complete stop. If there was no friction, the fan would spin forever.

If a rock is tied to the end of a string and rotated, circular motion is created in the rock. In this condition, if the string is suddenly broken, the stone will be thrown out along the tangent to the circle. The reason for this is that the rock wants to move in a straight line with the same momentum, i.e. at the same speed, due to inertia of motion when the string is broken. But the rock will run along a straight line? Now, since the velocity at every point of circular motion is tangential to the circle, the rock is thrown tangentially.
The lowest position A of the pendulum of an oscillator is when the oscillator is stationary or in equilibrium. When the mass is brought to position B and released, it moves towards A due to the attraction of the earth, but due to inertia of motion, it cannot stop at point A, it moves beyond point A to point C. Then again, the mass falls towards A due to the attraction of the earth. Thus, the pendulum oscillates in both directions until the air barrier stops the oscillation.

CONCEPT OF FORCE

Definition: An external force that changes or attempts to change the velocity of an object is called a force.

A force is a vector quantity. It has both value and direction. For example, sphere R is placed on a flat floor. In this case, let us assume that force F1 along BC or force F2 along OA is acting on the sphere R. The result of the action of these two balls will be different. Because, obviously the force F2 will only cause the sphere to move, while the force F1 will cause a rotation in the sphere.

INERTIAL AND NON-INERTIAL FRAMES OF REFERENCE

In discussing the motion of an object on or near the surface, the surface is assumed to be a fixed reference frame. A rock lying on the ground remains at rest unless an external force is applied. Again, even if a sphere is at rest on the floor of a train in uniform motion, the sphere is not moving unless an external force is applied.

Thus, it is seen that Newton’s first law of motion is applicable to a stationary or uniform motion system. Any such stationary or moving coordinate system is called an Inertial Frames of Reference. Not only the first law of motion, but all three of Newton’s laws of motion apply in any inertial frame.

On the other hand, suppose a sphere is stationary on the floor of a train. If the train is suddenly moving with forward acceleration, it is seen moving with spherical backward acceleration. In this case, even though no external force is applied on the sphere, the sphere does not remain stationary. So, it turns out that Newton’s first law of motion does not apply to a train moving with acceleration. Any system in motion with such acceleration is called an Non-inertial Frames of Reference. In fact, none of Newton’s laws of motion apply in inertial frames.

Newton First law of Motion: Inertia, Concept of force

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