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Susan MacIntosh, age 15, of Vancouver, D.C., Canada, for her question:

WHAT EXACTLY IS INERTIA?

Inertia has a part of the general area of gravitation. Sir Isaac Newton, who came up with the principle of gravitation and set forth a number of laws of motion, made it possible for us to understand a subject that is most complex.

Newton's Law of Inertia was also called the Law of Doing Nothing. Two parts of this law can be pointed out:

1  When a thing is moving, it does nothing of itself to change its motion.

An object will go on moving forever, in the same direction and at the same rate of speed, unless something else  another force  comes along to stop it, or turn it, or make it go faster or slower. FQr example, a bullet shot out of a gun would never drop to the ground if it were not for gravity's pull downward. Also, a person receiving a push or. a swing would go up and around the branch if it were not for friction that slows the swing, and gravity coming along to pull him back toward the earth.

A ball rolling on the ground stops because resistance of the air and the friction. of the ground stops it  or else it would go on rolling.

2  When a thing is at rest, it remains at rest, doing nothing, until something moves it.

A boulder on the around will not move unless someone picks it up or unless the earth next to it breaks away and the boulder falls into the hole. Big boulders moved under ice glaciers, but when the glaciers melted and the movement stopped, the boulders stopped.

It adds up to this: A thing in motion will go on moving and a thing at rest will go on resting.

The Law of Inertia gives proof to the Law of Conservation of Matter and Energy: Matter and energy cannot be made out of nothing; matter and energy cannot be destroyed. If . hings at rest could start moving of themselves, then the energy of motion would be created from nothing. If moving things could be stopped without something stopping .them, the energy of motion would be completely destroyed.

While the Law of Inertia was Newton's first law to explain motion, No. 2 states: The force required to set a body in motion or to stop a body already in motion is greater the greater the mass. Also, the force required is greater the quicker the motion. Law 3 states: Action and reaction are equal and opposite.

Think about that.

 

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