A Detailed Discussion of the Law of Inertia
Newton's first law of motion is also cited as the law of inertia.
This law states that a body continues to be in the state of rest or uniform motion along a straight line unless it is acted upon by an external force to change its state.
In our daily life, we find that a ball rolling on the ground stops after some time. This is because the frictional force of the ground is acting upon the ball to make changes in its state of motion.
The inertia of a body is measured by the mass of the body.
Heavier is the mass, greater is the force required hence, greater is its inertia and vice-versa.
Hence, Newton’s first law defines inertia, and it is justly called the law of inertia.
What is Inertia?
The inherent attribute of all the bodies, by virtue of which they oppose the change in the state of rest or of uniform motion along the straight line on their own, is called inertia.
Some real-life applications to describe the inertia are as follows:
Tables and chairs are kept inside the classroom and remain in a state of rest until someone moves them.
The reverse can also be true.
Suppose I am driving a car at a high speed. Suddenly, I encountered a big rock. I need to apply force to stop the car to bring it to a state of rest.
Inertia Examples
A few examples to describe the law of inertia in our everyday life are as follows:
When a bus starts suddenly, we fall backward. This is because our lower part of the body starts moving with the bus while the upper part tries to remain at rest.
Athletes run a certain distance before taking a long jump.
When a horse at full gallop stops suddenly, a man falls forward.
On shaking the mango tree, mango falls off the tree.
When a car rounds a curve suddenly, a driver is thrown outside.
Types of Inertia
Inertia is the resistance of a body to any change in its velocity.
It is of three types:
The inertia of rest: Tendency of a body to remain in the state of rest.
The inertia of direction: Tendency of a body to remain in a particular direction.
The inertia of motion: Tendency of a body to remain in a state of uniform motion.
Inertia of Rest
A body tends to remain at rest until an external force is applied to make it move. Therefore, the inertia of rest is an inability of a body to move and remain in the state of rest.
Example of Inertia of Rest
When we beat the carpet, it comes in motion, and dust particles are in a state of rest. This is because the dust particles tend to remain at rest, and hence get separated.
Inertia of Direction
The body tends to remain in the same direction until an external force acts upon it to make a change in its direction of motion.
The Inertia of Direction Examples
A few Real-life Examples are discussed below:
A bike tends to move in a straight line unless we turn the handle on the bike.
You use umbrellas to prevent yourself from getting wet. The direction of the raindrops is vertically downwards.
They cannot change their direction to make you wet.
When you spin the one end of a string tied to the stone. Suddenly the string breaks and stoneflies off along the tangent to the circle. This is because the pull in the string was forcing the stone to make a circular motion.
As soon as the string breaks, the pull vanishes, and the stoneflies off tangentially.
Inertia of Motion
The body continues to move in a uniform motion and the property under which it opposes the change in its present state is called the inertia of motion.
Examples of Inertia of Motion
Few real-life examples to describe inertia of motion are as follows:
When a train stops suddenly, we fall forward. By inertia of motion, the upper part of the body is in contact with the seat and starts moving with the train, while the lower part tries to remain at rest.
A person jumps out from a train and falls forward. This is because his feet are in contact with the ground and remain at rest while the remaining body continues to move because of inertia of motion.
Do you know?
Before Newton explained the three laws of motion, the great Greek thinker Aristotle put forward the concept that an external force is required to keep a body in motion. But he failed to realize that an opposite frictional force acts on the body to counter the external force so that the net force on the body is zero.
Sir Isaac Newton is regarded as the father of classical physics, owing to his laws of motion. The Law of Inertia is the name given to the first of these laws. The most significant and well-known is the law of inertia. Let's take a closer look at the first law of inertia in this essay.
Let's look at the definition of inertia before we go into the law of inertia. Unless acted upon by an external force, the matter has the property of inertia, which permits it to remain at rest or in uniform motion along a straight line.
What is the Inertia Law?
Newton's first law of motion, usually known as the law of inertia, asserts that unless an external force acts on an object, it will remain in either a condition of rest or motion. We have all heard of the Aristotle fallacy, which states that a body must always be propelled by an external force. When the concept of inertia was introduced, this was shown to be incorrect. Galileo discovered the notion of inertia with the following two tests.
Galileo and the Inertia Concept
The concept of inertia was created by Galileo, a leading scientist in the seventeenth century. According to Galileo, moving objects eventually come to a standstill due to a force known as friction. Galileo found that a ball would roll down one plane and up the opposite plane to roughly the same height in tests utilising a pair of inclined planes facing each other. The ball would roll up the opposite plane even closer to the original height if smoother planes were utilised. Any difference between the initial and final heights, Galileo reasoned, was attributable to friction. Galileo claimed that if friction were fully removed, the ball would soar to the exact same height.
Examples of the Law of Inertia
The lift began abruptly.
When a stationary bus begins to move, it has a tendency to move backwards.
When the lift suddenly operates, it causes a jerk.
When an abrupt break is applied, you can go forward.
Experiment
(Image Will be Updated Soon)
Visit Vedantu to learn more about the definition of inertia and the law of inertia. Get the best help from the subject matter experts online by logging into this site to clarify your doubts.
FAQs on Law of Inertia - Kinematics
1. What is the law of inertia in simple terms?
The law of inertia, also known as Newton's First Law of Motion, states that an object will stay at rest or continue moving at a constant velocity unless an external force acts on it. In simpler words, objects tend to resist changes in their state of motion.
2. Can you give some real-life examples of the law of inertia?
Yes, inertia is at play all around us. Here are a few common examples:
- Feeling a jerk on a bus: When a bus suddenly starts, you feel pushed back because your body's inertia tries to keep you in a state of rest.
- Shaking a rug: When you shake a dusty rug, the dust particles fly off because their inertia keeps them in place while the rug is moved away from them.
- Space travel: A spacecraft travelling in space continues to move at a constant speed without using fuel because there is no significant external force like air resistance to stop it.
3. How is an object's mass related to its inertia?
An object's mass is a direct measure of its inertia. The more mass an object has, the more inertia it has. This means a heavier object, like a large boulder, has a greater resistance to changing its state of motion compared to a lighter object, like a small pebble.
4. Is inertia a type of force?
No, this is a common misconception. Inertia is not a force. It is a fundamental property of matter that describes an object's natural resistance to any change in its motion. A force is a push or pull that can *cause* a change in motion, while inertia is the tendency to *resist* that change.
5. Does the law of inertia have its own formula?
The law of inertia itself is a qualitative principle and does not have a specific mathematical formula. It describes a concept. However, it is fundamentally linked to Newton's Second Law, which has the formula F = ma (Force = mass × acceleration). This equation shows how a force (F) is required to overcome an object's inertia (represented by its mass, m) to cause acceleration (a).
6. How does the law of inertia relate to the field of kinematics?
Kinematics describes the motion of objects (position, velocity, acceleration) without asking what causes the motion. The law of inertia provides the baseline condition for kinematics. It states that an object's velocity will remain constant unless a force is applied. This principle of constant velocity is a foundational scenario studied in kinematics.
7. What is the main difference between inertia and moment of inertia?
The key difference is the type of motion they relate to.
- Inertia describes an object's resistance to changes in its linear motion (moving in a straight line).
- Moment of inertia describes an object's resistance to changes in its rotational motion (spinning or turning). It depends on both mass and how that mass is distributed around the axis of rotation.
8. Why do we lurch forward when a moving car stops suddenly?
This happens because of your body's inertia. While the car is moving, you are also moving forward at the same speed. When the brakes are applied, they exert a stopping force on the car, but not directly on you. Your body's inertia makes it continue moving forward at the original speed until something, like a seatbelt, applies a force to stop you.
