Inertia: A Look At Newton's First Law of Motion

Newton's First Law is one of my favourite laws in physics, proposed by no other than the 17th-century scientists Issac Newton. He made other two laws to explain what happens to objects in motion or why they do not move. These three laws were popularly referred to as Newton's Three Laws of Motion.

^{[Image from Pixabay]Source: Rubber handhold in an empty commuter train to stabilise passengers from action of inertia}

The Newton's First Law of Motion, or as some people would call it, the law of inertia states as follows.

An object at rest stays at rest and an object in motion remains in motion with the same speed and the same direction unless acted upon by an unbalanced force.

In other words, terms:

An object at rest will stay at rest, forever, as long as nothing pushes or pulls on it. An object in motion will remain in motion, travelling in a straight line, forever, until something pushes or pulls on it.

In this law, there are conditions attached to have a balanced force.

1. The object is at rest, where the velocity V= 0 meters per second (object at rest); or
2. The object is in motion and V is not equal to zero. There is no change in direction or speed.

If the two conditions are correct, the object would forever continue on its way without any problem.

The forever part may be a bit hard to assimilate. Using a perfectly round ball bearing on a perfectly smooth inclined plane that stretches forever. A ball bearing kept on such a ramp and pushed downwards would roll down the inclined plane forever with no outside force interaction.

Or imagine a cart on a flat surface with at a speed of 3m/s, there is no friction between the tires and the ground, no air resistance, and no outside force of any kind. This cart would continue doing what it is doing (moving at a constant speed of 3m/s) forever unless an outside force causes a change in its motion.

On the other hand, if the cart is stationary, it would remain stationary (at rest) if there is no outside force acting on it.

The idea is that objects would forever do what "they are doing" until an outside force interacts with them.

Inertia is the tendency of an object to continue in its state of motion or rest. In other words, an object's tendency to resists a change of its state of motion.

Inertia and Mass

Inertia is has a direct relationship with a mass of an object. For instance, a 200kg sumo wrestler and a small 80kg sumo wrestler are at rest. Which of this two wrestler do you think can move easily?

It is a no-brainer question as you already know the smaller wrestler is the one that would find it easier to move.

The smaller sumo wrestler has less mass so that his body would offer less resistance when an outside force ( a push from the big wrestler) acts on it. The big sumo wrestler provides more resistance to change of its position due to the more significant mass.

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Some Application of Inertia in Everyday Life

The seatbelts play a big role in safety due to its effects to counteract the inertia experienced when a car travelling at a certain speed is abruptly brought to a halt. The car will flip the passenger off as shown by this gif.

But with a seat belt in place, the tendency of the body to continue with the velocity of the acceleration of the car before it hits the wall gets countered by an opposing force; which the seat belt provides.

If you have suddenly experienced sitting in a powerful car that did a 0 to 60-mile acceleration in less than 3 seconds, or just about any car that did a sudden acceleration, it would feel as if someone is pressing you into the car seat. But after some seconds, the "pressing force" stops as the car enters into a constant speed.

That phenomenon is just your inertia wanting to keep you at rest as the car surges forward, but the car seat would oppose this from happening. But when a constant speed is attained, due to no acceleration, that is the acceleration at this point is equal to zero, the force is balanced, and the occupants do not feel any opposing force.

Also, the raised headrest prevents injuries to occupant's neck when the vehicle is hit from behind.

When a car gets struck from behind, the vehicle experiences a sudden acceleration, and the head and neck are suddenly thrust back, but the car headrest counteracts this movement and suppresses this shock that may cause a neck injury.

^{Gifs: Inertia in real life}

The man that stepped off the train (shown in the gif above) and fell was as a result of inertia. The train was in motion when he stepped out. The inertia wanted him to continue in its present state of motion. He could have counteracted it by running as soon as he stepped on the ground and slowly stop. The paramedics should have secured the victim on the back of the car before accelerating off.

The pulling of tablecloth off a table with objects on it may look like magic of some sorts, but that is merely inertia. The tendency of the objects to remain at rest was all there is to this trick. Even though the speeding tablecloth underneath the object as its yanked off, the object remains at rest.

The trick is to have as little friction as you can between the object and the table. This trick you could do by having a smooth table surface and a cloth with less friction so that the object does not get pulled by the friction generated between it and the cloth.

^References

• ^{Newton First Law of Motion}

• ^{Law of inertia vs Seatbelts}

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^{Image/Gif Reference}

^{Sumo wrestlers}

^{Gif Showing car suddenly brought to rest by a wall}

^{Gifs: Fall from train|Fall from moving car}

^{Gif:Pulling a cloth off table with objects trick}

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