INERTIA

 

The Great Physicist and inspiration of all the physicists, Albert Einstein once said that “Nothing happens until something moves”. In other words, for something to happen in our life, we must make something happen. So many fail because they don’t get started and they don’t overcome Inertia. Inertia refers to inaction, lack of desire to change or move. If you want to experience something, you must take action.

Sometimes, you make up your mind about something without knowing, Why? When a person is inexorable then, he can’t be convinced to change his mind, no matter what. His decisions persist by inertia and it gets harder to change with time. Cognitive inertia is the reason that changing our habits can be difficult. 

Sometimes inertia help us. After all, questioning everything would be exhausting. But, in many cases, it is worthwhile to overcome inertia. To improve, to progress, for transition and for the development of our society and nation, we need to change for a novel approach. Many times, a trigger is required for things to happen for a change. 

The German Astronomer Johannes Kepler coined the word "INERTIA" in his Epitome Astronomiae Copernicanae, which he derived from the Latin word for "idleness" or "laziness" was not quite the same as its modern interpretation.

Kepler defined inertia based on the presumption that rest was a natural state which did not need explanation.

Inertia refers to resistance to change — resistance to changes in the state of motion or in the minds of people. 

In the Physics language, Inertia refers to the inability of a body by virtue of which it can’t move by itself. A body at rest remains at rest and can’t start moving on its own. It is the tendency of a body to oppose any change in its state of rest or of uniform motion.

Types of Inertia:

Inertia of rest: The tendency of a body to oppose any change in its state of rest. For example, When a bus starts suddenly in forward direction, the passengers in the bus fall backward due to inertia of rest.

Inertia of motion: The tendency of a body to oppose any change in its state of uniform motion. For example, the passengers fall forward when a fast-moving bus stops suddenly due to inertia of motion.

Inertia of direction: The tendency of a body to oppose any change in its direction of motion. For example, When a fast-moving bus negotiates a curve on the road, passengers fall towards the center of the curved road.

When a horse starts running suddenly, the rider falls backwards due to the inertia of rest. Similarly, when a running horse stops suddenly, the rider falls off because the rider's body continues to move due to inertia of motion.

Consider an index card placed on the top of a glass with a penny on the top of it. If the index card is removed quickly, penny falls straight into the glass due to inertia of rest.

When we stir coffee or tea and stop, the swirling motion continues due to inertia of motion.

Inertia enables ice skaters to glide on the ice in a straight line.

When we shake the branches of a fruit tree, branch comes to motion. But fruits remain at rest due to the inertia of rest and fall down.

When a carpet is beaten with a stick, dust particles come out due to the inertia of rest.

When a bullet is fired against a glass window pane, it makes a hole, without making any crack in it. Initially, the entire glass is in the state of rest. When a bullet strikes the glass pane, the part of the glass pane which comes in contact with the bullet immediately shares the large velocity of the bullet and flies away making a hole. The remaining part of the glass remains at rest and is not cracked.

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René Descartes was known amongst the learned in his days as a creative Mathematician and Natural Philosopher. He said that to understand the motion of objects, it is necessary to understand its cause, its universal and particular cause. Universal and primary cause, which is the general cause of all motions in the world, is nothing other than God Himself who in the beginning created matter together with motion and rest and now conserves just as much motion and rest as a whole as He then posited. And then its particular cause, by which it happens that individual parts of matter acquire motions that they did not have before, when impelled to do so by some cause. 

In a letter, he concluded:

“I do not recognize any inertia or natural sluggishness in bodies…; and I think that by simply walking, a man makes the entire mass of the earth move ever so slightly, since he is putting his weight now on one spot, now on another. All the same, I agree …that when the largest bodies (such as the largest ships) are pushed by a given force (such as a wind), they always move more slowly than others.”

Descartes found the existence of “forces of resistance” (or “natural sluggishness”). Bodies are “indifferent to motion”, so even the slightest weight should move the entire earth. On the other hand, he was willing to acknowledge the commonly observed fact that larger objects are much harder to set in motion than smaller objects.

Inertia and mass: It’s more difficult to move a heavier object as compared to a lighter object. Therefore, heavier or massive object offer large inertia. Similarly, if you want to stop a lighter and a heavy body moving with equal velocities, you may stop a lighter body with your hand(depending on its velocity), while the heavier one may slow down only a little(depending on its velocity). Larger the mass, larger is the inertia, we may say mass is a measure of its inertia.

Galileo Galilei was an Italian Astronomer and Physicist. He was born in the city of Pisa. Galileo has been called the "Father of Modern Physics”.

Galileo demonstrated two experiments to explain the concept of inertia.

An objects moving down an inclined plane accelerate (i), while those moving up retard (ii) and Motion on a horizontal plane is an intermediate situation (iii).

Galileo concluded that an object moving on a frictionless horizontal plane must neither have acceleration nor retardation, i.e. it should move with constant velocity.

A ball released from rest on one of the planes rolls down and climbs up the other and the final height of the ball is nearly the same as the initial height (a).

If the slope of the second plane is decreased and the experiment repeated, the ball will still reach the same height, but in doing so, it will travel a longer distance (b). In the limiting case, when the second plane is i.e. is a horizontal the ball travels an infinite distance(c).

In practical situations, the ball will stop after travelling some distance because of the presence of frictional force acting opposite to the direction of motion.

Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the classical mechanics developed by Sir Isaac Newton. 

Newton presented three fundamental laws that govern the motion of objects. These three laws are known as Newton’s laws of motion. Newton’s first law is also called as law of inertia which states that "Everybody continuous in its state of rest or of uniform motion in a straight line unless compelled by some external unbalanced force (cause) to change that state".