Define Inertia of motion with 10 visual examples, formula and Application

Define Inertia of motion with 10 visual examples, formula and Application

Aditya Raj Anand

Thursday, 2 January 2025

Physics

After a long discussion on Inertia of rest. The time has come to talk about inertia of motion. Not only the definition but also 10 examples of inertia of motion that we have all experienced in our day to day life.

But before we go further, let's make a table of contents for this post.

Topic covered in this lecture

• What is an Inertia of motion?
• Formula of inertia of motion.

Q. What is inertia give an example of inertia of motion also explain which of the following has more inertia an empty box or a box full of books?

• Daily life examples of inertia of motion with visual picture.
• Application of inertia of motion.
• Where is Inertia of motion came from?
• Why inertia of motion related to Newton's first law of motion?

All the above topic are well explained in the following notes. So let's start.

What is inertia of motion?

If we talk about only inertia, neither rest nor motion. Then it is a tendency of a body to keep their original state.

So, Inertia of motion is defined as the tendency of a body to keep their original state of motion forever. Untill or unless an external force is applied to it.

Please note that :- In inertia of motion, the direction of the moving object also constant. Means will be moving in only one direction forever.

Let's take an example to understand the inertia of motion more clearly.

Case 1:- 

Suppose a car is running on a straight road at a speed of 40 km/h. After 5 hours of constant moving, a curve turning has come. Now, if we didn't apply the external force (or brake) the car will be accident.

But if we apply the brake to the car, suddenly we feel a forward jerk. This jerk is because of inertia of motion.

This explains as follows : When we apply the brake the car has stopped but our body has a tendency to keep their original state of motion. Due to this we feel jerk in the forward direction.

Case 2:- 

Suppose the same car is running on a straight road at a speed of 40 km/h. After 3 hours of constant moving a road breaker has come. 

Now, when the car cross the breaker, the wheel of the car leave the ground for some minor second and after that it again touches the ground.  But due to this we felt a jump inside the car. 

This jump is because of inertia of motion. This explains as follows:

While the constant moving of the car. Our body is in state of rest with respect to other person inside the car. But in motion with respect to the people who has seen from outside the car.

Please note that :- This case is also a good example of rest and motion are relative terms.

So, after crossing the road breaker our body gain some motion but after some micro second it again touches the ground. So we felt jump in upward direction.

Case 3:- 

Suppose, we are sitting in the same car. After some time, if we change the direction of the car. We felt down in the right side because of the inertia of direction.

Rest and motion are relative terms.

Suppose a person is standing on the moon. We can say that person is in state of rest with respect to another person stand beside them. But in motion with respect to that person who seen both of them from earth.

Let's take another example to illustrate our above example.

Suppose we are sitting on a running train. Here we can say that we are in state of rest with respect to other passages sitting besides us. But we are still in motion with respect to the passages standing on the platform.

formula of inertia of motion

Please note that there is no definite formula to calculate the inertia of motion, rest or direction.

Inertia is a phenomenon in science. It is not a mathematical concepts or equations.

The inertia of momentum has a formula. But not inertia of motion.

Inertia of motion is used to understand the concept of the questions. Inertia can be used to clean the concept of Newton's first law of motion.

Q. What is inertia give an example of inertia of motion also explain which of the following has more inertia an empty box or a box full of books?

In most simple words, Inertia is the tendency or behaviour of a body that helps them to keep their original state unless or until an external force is applied to it.

Please not that the body may be in state of rest or motion.

Example of inertia of motion.

Applying brake suddenly when the car is in motion. This explains as follows:

When the car is moving in a straight line at constant speed. And if we apply the brake, it goes slow down and Stop after some time. Due to the inertia of motion. Because the moving car always wants to remains in motion as according to Newton's first law. But when we apply brake, Newton's law break. That's the reason we feel forward force after applying brake.

Now, the question is which has more inertia.

1. An empty box.

2. A box with full of books.

Hence, to answer this question. Let's first understand that the object which has more masses has more inertia than the lighter one.

So, here the box full of books has more inertia than the empty box.

Daily life examples of inertia of motion with visual picture

1. Feel backward force when car suddenly start.
2. Feel forward force when car suddenly stops.
3. Collision of moving objects in space.
4. Moving of satellite in space.
5. Moving of planets in space.
6. Jump from moving train.
7. Objects come to you when throw inside the moving train.
8. Athletes not stop running even after reach to the final position.
9. The moving of bike for some time, even we off the engine.
10. Continuous moving of stone attached with thread in circular path.

These are the 10 most common and familiar examples of inertia of motion that we have expressed in our life.

1. Feel backward force when car suddenly start.

When a car suddenly starts, you feel a backward force because of inertia, which is a property of matter described by Newton's First Law of Motion. Here's an explanation of why this happens:

Inertia is the tendency of an object to resist changes in its state of motion. According to Newton's First Law, an object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by an external force.

When you are sitting in the car at rest and the car suddenly accelerates forward:

The car starts moving forward, but your body, which was initially at rest, tends to stay in the same position because of inertia.

To compensate for the sudden acceleration, your body resists the forward motion, which causes you to feel as if you're being pushed backward relative to the car.

2.Feel forward force when car suddenly stops.

When a car suddenly stops, you feel a forward force due to inertia, which is a consequence of Newton's First Law of Motion. Here's why this happens:

Inertia and Newton’s First Law of Motion

Inertia is the tendency of an object to resist changes in its state of motion. According to Newton's First Law, an object will remain in its current state of motion (whether at rest or moving) unless acted upon by an external force.

When the car suddenly stops:

The car decelerates (slows down) quickly, but your body, which was moving forward with the car, wants to keep moving at the same speed because of its inertia.

Since your body tends to keep moving forward while the car is now decelerating, you feel as if you are being pushed forward.

Understanding the Force

As the car comes to a sudden stop, it exerts a backward force on you (via the seat and seatbelt).

Your body resists the sudden deceleration and wants to continue moving forward.

The forward force you feel is your body’s resistance to this change in motion. Essentially, you're trying to maintain the forward velocity that you had before the car stopped, and this results in the sensation of being pushed forward.

This is why you feel like you're being pushed forward when the car suddenly stops. The seatbelt or any other restraint system in the car works to counteract this forward motion by applying a backward force to bring your body to a stop along with the car.

3. Collision of moving objects in space.

Collisions between moving objects in space can occur in a variety of scenarios, such as the collision of asteroids, comets, spacecraft, or even smaller particles like space debris. These collisions are governed by the basic principles of physics, including momentum conservation, energy conservation, and the laws of motion.

Key Concepts in Collisions of Moving Objects in Space:

1. Conservation of Momentum: In an isolated system, where no external forces are acting, the total momentum before the collision is equal to the total momentum after the collision. This is a fundamental principle known as conservation of momentum. Momentum ($p$) is the product of an object's mass and its velocity ($p = mv$).

   • If two objects collide in space, their combined momentum before and after the collision remains the same, assuming no external forces (like gravity or friction) are involved during the brief time of the collision.

2. Conservation of Energy: In the case of elastic collisions, both kinetic energy and momentum are conserved. However, in inelastic collisions, while momentum is conserved, some of the kinetic energy is transformed into other forms of energy, such as heat, sound, or deformation (like crumpling in the case of spacecraft).

   • In space, the lack of air resistance means that energy lost as heat or sound might not dissipate in the same way as on Earth, but energy still gets converted into other forms (e.g., deformation of objects or the production of heat).

3. Types of Collisions:

   • Elastic Collision: Both momentum and kinetic energy are conserved. After the collision, the objects bounce off each other without any permanent deformation. This is a rare occurrence in space since most space objects are not perfectly rigid.

   • Inelastic Collision: Momentum is conserved, but kinetic energy is not. Some energy is lost, and the objects may deform or break apart. For example, when two asteroids collide, they might break into fragments, and the fragments might continue to move with the combined momentum of the original objects.

   • Perfectly Inelastic Collision: This is the extreme case where the colliding objects stick together after the collision, moving as one mass with the combined momentum. This type of collision is also common when large objects like asteroids collide, often resulting in the formation of a new, single object.

4. Force of Impact: The force experienced during a collision depends on the change in momentum and the duration of the collision. In space, objects like asteroids or comets have extremely high velocities, so even a seemingly small change in velocity can result in a significant release of energy.

5. Relativistic Effects: In high-speed collisions (i.e., when objects approach significant fractions of the speed of light), relativistic effects become important. In such cases, both momentum and energy must be considered in the relativistic form, which takes into account the increase in mass as an object approaches the speed of light.

Example: Collision of Asteroids in Space

• Suppose two asteroids are on a collision course, moving at velocities $v_1$ and $v_2$, and have masses $m_1$ and $m_2$, respectively. The total momentum before the collision would be:

  $$p_{\text{total}} = m_1 v_1 + m_2 v_2$$

  After the collision, if the asteroids collide elastically, the velocities change, but the total momentum remains the same. However, if the collision is inelastic, the kinetic energy will be partially converted into other forms of energy, such as heat or deformation.

Outcome of Collisions in Space

• Creation of Craters: The collision of large objects (like asteroids) can create craters on planets or moons, as seen in Earth's history with the impact that contributed to the extinction of the dinosaurs.

• Fragments and Debris: If objects collide with high velocity, they may break into smaller fragments. These fragments could continue to move through space, potentially causing further collisions.

• Spacecraft Collisions: In the case of spacecraft, a collision could be catastrophic. Spacecraft and satellites often take precautions to avoid collisions with space debris, which can cause significant damage at high speeds, despite the lack of atmosphere in space.

Conclusion

Collisions in space, although occurring in the vacuum of space where there is no air resistance, still obey fundamental physical laws, particularly the conservation of momentum and energy. The outcomes of these collisions depend on the types of objects involved, their velocities, and the nature of the collision. The lack of atmospheric drag means that objects continue moving with high velocities post-collision, which could lead to lasting effects like fragmentation or the creation of new objects.

4. Moving of satellite in space.

Satellites in space move according to the principles of orbital mechanics, primarily governed by the gravitational force and centripetal force. Here’s an explanation of how satellites move in space:

1. Orbital Motion and Gravitational Force

A satellite in orbit around a planet or other celestial body is essentially in free fall, constantly being pulled toward the planet by gravity. However, its tangential velocity (speed in a direction perpendicular to the force of gravity) keeps it from falling directly to the surface.

The gravitational force between the planet and the satellite provides the centripetal force that keeps the satellite in orbit.

Inertia causes the satellite to move in a straight line unless acted upon by an external force, while gravity continually pulls the satellite toward the planet, creating a curved path. This balance of forces results in the satellite continuously "falling" around the planet, maintaining its orbit.

5. Moving of planets in space.

Inertia: According to Newton’s First Law of Motion, an object in motion tends to remain in motion at a constant velocity unless acted upon by an external force. In the case of a planet, its inertia wants it to move in a straight line, but the Sun’s gravitational pull prevents it from flying off into space.

Thus, planets move in orbits, constantly falling towards the Sun due to gravity, but their inertia causes them to keep moving forward, creating an elliptical orbit.

6. Jump from moving train.

Jumping from a moving train is extremely dangerous and should be avoided at all costs. However, understanding the physics behind it helps explain why it’s so risky. Here’s what happens:

When you're inside a moving train, you are moving at the same speed as the train, relative to the ground outside. If the train is moving at 50 km/h, you, along with everything inside, are also moving at 50 km/h in the same direction as the train.

Relative to the train: You are stationary in the train.

Relative to the ground: You are moving at the same speed as the train.

When you jump off the train, your body still retains the horizontal speed of the train (50 km/h, for example) at the moment you leave it, since there is no external force to stop that horizontal motion immediately.

What Happens When You Jump Off : At the moment you jump, you maintain the horizontal velocity of the train. This means that even after leaving the train, you will still be moving forward at the same speed as the train (unless air resistance or friction acts on you).

7. Objects come to you when throw inside the moving train.

In a moving train, if you throw an object backward, it might appear to come toward you relative to your position inside the train, because you and the object are both moving forward at the same speed as the train. However, relative to the ground outside, the object retains the train's speed (forward or backward), and its motion is adjusted accordingly.

When you throw an object inside a moving train, the behavior of the object depends on the relative motion between you, the train, and the object.

8. Athletes not stop running even after reach to the final position.

Athletes continue running even after reaching the finish line due to their inertia, momentum, and the need for gradual deceleration to avoid injury. The combination of physiological and psychological factors means that it takes a moment for them to stop, even after they've crossed the final position in a race.

When athletes run in a race and continue running even after reaching the final position, it’s due to several factors related to inertia, momentum, and reaction to the environment. Here's an explanation of why this happens:

Inertia and Momentum :-

Inertia is the tendency of an object to resist changes in its motion. According to Newton's First Law of Motion, an object in motion will stay in motion unless acted upon by an external force.

When an athlete is running at high speed, they have momentum — the product of their mass and velocity. Even if they reach the finish line, their body will want to continue moving due to inertia, which means they will keep running for a brief moment after crossing the finish line.

9. The moving of bike for some time, even we off the engine.

When a bike continues to move for some time even after the engine is turned off, it is due to the concept of inertia and the momentum of the bike. Here's an explanation of what happens:

Inertia and Momentum :- Inertia: According to Newton’s First Law of Motion, an object in motion will remain in motion unless acted upon by an external force. In the case of the bike, the inertia of the bike's motion makes it continue moving even after the engine is turned off.

Momentum: The bike has momentum — the product of its mass and velocity. When the engine is running, the bike gains momentum as it moves forward. Even after you turn off the engine, the bike retains this momentum and will continue moving forward for a while until external forces (like friction, air resistance, and the brakes) slow it down.

10. Continuous moving of stone attached with thread in circular path.

Inertia of the Stone :- The stone has inertia, which is its tendency to resist changes in motion. If there were no force acting on it, the stone would move in a straight line tangent to the circular path at any point.

However, because the thread pulls the stone toward the center, it prevents the stone from flying off in a straight line. The result is that the stone moves in a circular path instead.

Application of inertia of motion.

• Application of car brakes, train brakes etc works on the inertia of motion.

• The runner athelete also uses the application of inertia of motion for long jumping.

• The scientist also uses the application of inertia of motion in space satellite.

• The study of the motion of earth and other planets can be understood by the application inertia of motion.

• Aeroplane take off and landing is also use application of inertia of motion.

Why inertia of motion related to Newton's first law

According to Newton's first law of motion, a rest body always remains in state of rest and a moving object always in state of motion.

Hence, inertia of motion said that, a body which is moving with some velocity. It always moving forever until or unless an external force is applied to it.

So, the definition of both the term are inter relative. Not only the definition but also the concept of both the terms are co-related.