Topic 4

Who is this guy Newton?

Isaac Newton

Aristotle BC 384-322

The heavenly realmaether

Galileo Galilei (1564-1642)

Galileo’s Principle of Inertia

The natural state of a moving body is to continue moving in a

straight line.

Why ?

Why?

Law I

• Every body perseveres in its state of being at rest or of moving uniformly straightforward, except insofar as it is compelled to change its state by forces impressed.

p. 117- text

( Law of Inertia)

Law II

• A change in motion is proportional to the motive force impressed and takes place along the straight line in which that force is impressed.

p. 117- text

What’s Momentum?

• Momentum is mass times velocity of an object.

p = mv

Law III

• To any action there is always an opposite and equal reaction; in other words, the actions of two bodies upon each other are always equal and opposite in direction.

p. 117- text

So mass is not weight?

• You need the mass of an object to get it’s weight. Mass is the amount of matter in an object, while weight is the force acting on that object’s mass… as if it were accelerating to the center of the earth.

• Yes!

Recall Newton’s 2nd Law

Descartes’ Book on motion:

Principles of Philosophy

Newton’s Book on motion:

Mathematical Principles of Natural Philosophy