Newton’s Laws of Motion

This is interesting because Sir Isaac Newton formulated these Laws from simple observations, exactly akin to the observations on this blog.

No, the apple did not fall on his head.

Here are the Laws:

Newton’s First Law: (N1) “A body at rest will stay at rest, and if being translated at a constant velocity, will keep on being translated at a constant velocity, unless acted upon by an external force”

Newton’s Second Law: (N2) “The resultant force on a body is equal to the rate of change of momentum of that body”

Newton’s Third Law: (N3) “To every action there is an equal and opposite reaction”

The qualifying terms are: “Body”, “Force”, “Translated”, “Velocity”, “Momentum”, “Action”, “Reaction”. However, definitions will follow more easily if the “common sense” Laws are given first.

N1: “If you push a stopped thing it goes, and if you don’t, it won’t.” and

“ If you push something already going, it will either slow down or speed up, depending on which way you push.”

N2: “F = ma” or “Force equals mass times acceleration”

N3: “Push something and it will push back”.

Before the definition of the qualifying terms, some examples will clarify.

N1: Every thrown ball slows down and stops, because of air resistance.

N2: If you keep your foot down on the gas pedal in a car, it will get more and more fast.

N3: In empty space, if an astronaut pushes another astronaut, both will move away from each other at the same rate.

Definitions:

“Body” = anything that can move.

“Force” = a constant pushing.

“Translated” = moved in a straight line.

“Velocity” = speed in one direction only.

“Momentum” = mass x velocity

“Action” = a particular push.

“Reaction” = a particular push back.

Well, these are they. Apply these in the right way, and a lot of problems can be solved about things that move.

The trouble is, knowing which one to use in each situation.

There are more ways of formulating the Laws, but as given, the first set are the “official” versions, whereas the second set are the “normal “ versions that everyone has heard at least once.

The most used is the second. It crops up everywhere. Especially interesting is the case of applying it to a space rocket being launched, but that involves a real knowledge of calculus to solve (clue – you actually need the “official” version of N2, the “normal” N2 is insufficient!).

As a nuclear scientist, I use N1 quite a bit.