Newton's Life and Laws

Library of Congress

Early Work on Optics

Observation of Halley's Comet

Work at Cambridge

"I never saw him take any Recreation or Pastime, either in

Riding out to take the Air, Walking, Bowling, or any other Exercise whatever, Thinking all Hours lost that was not spent in his Studies, to which he kept so close that he seldom left his

Chamber."

Newton was interested in solving mathematical problems that

had gripped people. This was a guy who adored computation of every kind. Among the things

that you can see if you open his manuscripts, for instance, is there are places where you'll

find he's calculated logarithms out to 50 places and things like that. Not because he needed it, but because he liked doing it. I mean, it was a pleasure to him to do that sort of thing. He was an unusual sort, obsessive, but gripped by the power and the beauty of sheer computation. I think that was a driving force

behind what he did.

Buchwald 2006

'How to draw tangents to mechanical lines'

The Three LawsAccording to Newton

Law I: Every body perseveres in its state of being at rest or of moving uniformly straight forward, except

insofar as it is compelled to change its state by force impressed.

Your book: An object at rest will remain at rest, and an object in

motion will continue to move in a straight line with constant speed, if and only if the net force acting on

that object is zero.

Law 2: The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on

which that impulse is impressed.

Your book: The acceleration of an object is equal to the sum of the forces acting on the object,

divided by the mass of the object.

F=ma

How can you change your acceleration without a force?

Mass can change! So, in absence of friction, a car will accelerate slightly as it runs out of gas.

Some animals can change their shape in clever ways that make them accelerate without forces. One example is a cat, which can turn in mid air. Another example is a bacterium, which twists its tail to give an apparent acceleration without a force.

Gravity! According to relativity, objects move in perfectly straight lines—it's space that's curved.

Score one for Newton.

Forces and Accelerations are VECTORS

Law 3: For a force there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in

opposite directions.

Your Book: The force of A on B is equal in magnitude and opposite in direction of the force

of B on A

-> try it!