What Is Inertia

Newton’s first law of motion is based on a property which is present in every inanimate object. The law deals with our everyday experience where we see objects that are unable to change their physical state of rest or uniform motion. These non-living objects remain in a particular state until or unless an external factor such a force is applied on it. This property is known as inertia.

Historical facts about inertia
Aristotle was the first one to note this physical property of inanimate objects as he clearly stated that, “ an object in rest remains in rest and object in motion remains in the absence of any power. In 16th century, Nicolaus Copernicus stated that every object on earth is always in motion and not in rest as earth is in constant motion, revolving around the sun. Galileo enhanced Copernicus conclusions that every object on earth will resist a change until it is disturbed. Yet, it was Newton who summed up everything in his Laws of motion and gave it a new direction by defining a physical property known as force.

Understanding Newton’s First law of motion   
In his first law, Newton describes two properties, inertia and force. He said, a material object remains in one state (or retains its inertia) unless a force is applied on it. A material object can either have inertia of motion or inertia of rest at a particular moment in time. Lets take some real life examples to understand inertia of motion and inertia of rest.

  • Whenever a bus suddenly starts all standing passengers are pushed backwards. The reason is inertia of rest of the upper body. When a person is standing in a bus his or her upper body is in rest and when the bus suddenly starts, he or she experiences a sudden force in the form of push.
  • Similarly if the bus suddenly stops then all standing passengers falls in front because their upper body is in inertia of motion. They experience the pull because their upper body  remains in motion even though their lower body has come to rest.
  • Why a bullet cuts a hole in window pane? The answer is inertia. A bullet hit brings the portion of window in inertia of motion whereas its neighboring portion remains in inertia of rest.
  • You must have seen the card and coin magic. Its not magic it is inertia. A coin is placed over a card and the card is placed over a glass.

When the card is quickly pulled then the coin falls in the glass. The reason is inertia of rest of the coin and the sudden force pulls its down.

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