Law of Inertia is another name for the First Law of Motion given by Sir Isaac Newton. As Law of Inertia has been studied by various scholars, throughout the centuries, and it helped humanity to understand the various concepts of motion in a wide range of fields from aerospace to automobile design.
The origins of the Law of Inertia can be traced back to the ancient Greek philosophers such as Aristotle and Galileo, who first posited the idea of “natural motion.” But until Sir Isaac Newton redefined the Law of Inertia as the “first law of motion” in the 17th century, it was not widely used by science scholars. Their Law of Inertia is also called Newton’s First Law of Motion. In this article, we will dive deeper into the concept of the Law of Inertia and other related topics in good detail.
Inertia is the basic concept of physics that is explained using the concept of Mass. The inertial concept was first explained by Sir Isaac Newton and the Law of Inertia is explained as any object in a state of rest or in a state of motion always staying in its state of rest or motion until an external force is applied. We can define Inertia in physics as the property of the matter that is linked to the mass of the object.
In this article, we will learn about, What is Inertia, What is Law of Inertia, Examples of the Law of Inertia, and others in detail.
What is Inertia?
Inertia meaning is the property of any material by the virtue of which any object tends to be in the state of rest or motion and does not change its state of rest or motion until an external force is applied to it. We define the inertia of any object as,
“The property of any object by the virtue of which the object cannot change its state of either in rest or in motion is known as Inertia.”
The mass of a body is responsible for creating inertia, the greater the mass of a body, the greater will be the inertia of the body. For instance, It is easy to stop by simply applying braking to a bicycle as the mass of the bicycle is less but it is a lot tougher to stop a bus or a truck, since the mass of a bus or a truck is more. The same is the case when these vehicles are to be started, more effort in bus/truck (since more mass) and less effort on a bicycle (since less mass).
Inertia Definition
Initially, when the concept of inertia was not introduced, Aristotle came up with a hypothesis regarding the objects in motion, which later proved to be false. Therefore, the concept of objects in motion given by Galileo is known as Aristotle’s fallacy.
Aristotle’s fallacy was based on the everyday observation of objects in motion. Imagine a ball in motion which was thrown some time ago, after some time, the ball has to come to rest. Aristotle presumed this to be a natural phenomenon and not an act of friction and hence claimed that an object in motion always has some external force applied to it, to else it shall come to rest. This concept contradicts the concept of inertia. So we define Inertia in Physics as the property of the material based on its mass.
What Is Law of Inertia?
The law of inertia also called the first law of motion is the fundamental law of physics that was proposed by famous English Scientist Sir Issac Newton, the law of inertia states that,
“An object in the state of rest or motion always remains in its initial state until and unless external force is applied to it.”
Law of Inertia Examples
Various example explaining law of inertia are,
A ball rolling on a frctionless table in a vacuum rolls for infinity until an external force is applied to it.
A person standing on a moving bus titls forward when the brakes of the bus are applied.
Shaking the branches of the tree with fruits makes the fruits to fall on the ground because they are in the state of rest, etc.
Types of Inertia
There are three types of Inertia that are,
Inertia At Rest
Inertia In Motion
Inertia Of Direction
Now let’s learn about them in detail
Inertia At Rest
A body remains at rest due to the inertia (opposing force) present inside the object until and unless an external force more than the inertial force is applied to it.
Inertia In Motion
A body in motion remains in motion until and unless an external force (maybe brakes, friction, etc) is applied to the body.
Inertia Of Direction
A body moving in one direction remains in the same direction until and unless some force is applied in order to change the direction of the body.
Galileo’s Free Fall Experiment
The concept of inertia was established by Galileo. It states that if an object is free-falling or rolling down an inclined plane, the distance traveled by the object is directly proportional to the time. Let s be the distance and t be the time traveled then
s ∝ t2
Similarly, when the slope of the plane is completely removed, the ball shall reach infinity but due to the presence of friction, it stops after a certain point. Therefore, Aristotle’s concept was turned out to be false, since if any friction is not present (assuming), an object in motion shall always remain in motion.
Inertia Exlpain by Galileo
In the conclusion of his free falling experiment Galileo conclude that, Inertia is the internal property of the material and its is responsible for its state of rest or motion and changing the state of inertia requires an external force. This is later confined by Issac Netwon in his Newton’s Laws of Motion.
Inertia and Mass
Inertia is a quality of all objects made of matter that possess mass. They keep doing what they are doing until a force changes their speed or direction. A ball sitting still on a table won’t start rolling around unless something pushes on it, be it your hand, a gust of air, or vibrations from the surface of the table. If you tossed a ball in the frictionless vacuum of space, it would travel on at the same speed and direction forever unless acted on by gravity or another force such as a collision.
Mass is a measure of inertia. Objects of higher mass resist changes in motion more than objects of lower mass. A more massive ball, such as one made of lead, will take more of a push to start it rolling. A styrofoam ball of the same size but low mass may be set in motion by a puff of air.
Theories of Motion From Aristotle to Galileo
In everyday life, we see rolling balls come to rest. But they do so because they are acted on by force of gravity and from the effects of friction and air resistance. Because that is what we observe, for many centuries Western thought followed the theory of Aristotle, who said that moving objects would eventually come to rest and needed continued force to keep them in motion.
In the seventeenth century, Galileo experimented with rolling balls on inclined planes. He discovered that as friction was reduced, balls rolled down an inclined plane attained almost the same height rolling back up an opposing plane. He reasoned that if there were no friction, they would roll down an incline and then keep rolling on a horizontal surface forever. It wasn’t something innate in the ball that caused it to stop rolling; it was contact with the surface.
Newton’s First Law of Motion and Inertia
Isaac Newton developed the principles shown in Galileo’s observations into his first law of motion. It takes a force to stop the ball from continuing to roll once it is set in motion. It takes a force to change its speed and direction. It doesn’t need a force to continue moving at the same speed in the same direction. The first law of motion is often referred to as the law of inertia. This law applies to an inertial reference frame. Corollary 5 of Newton’s Principia says:
The motions of bodies included in a given space are the same among themselves, whether that space is at rest or moves uniformly forwards in a straight line without circular motion.
In this way, if you drop a ball on a moving train that is not accelerating, you will see the ball fall straight downward, as you would on a train that was not moving.
