The History of Scientific Thought about Forces &

Motion

Aristotle 384 B.C. – 322 B.C.

¨ Greek scientist & philosopher

¨ Made scientific discoveries through careful observations and logical reasoning.

Aristotle believed all motion is linear on the planet Earth: meaning everything moves in a straight line. If I throw this rock, it will travel in a straight line, and also fall in a straight line….

                                  

The way Aristotle thoughtprojectiles moved

The way projectiles "really" move

When a feather and rock are dropped at the same time, the rock will fall to the ground first. Aristotle believed that the Earth pulls on objects according to their weight.This means that a large heavy object will fall to the ground faster than a large light object

                   

        Aristotle Reality      

                   

Galileo Galilei 1564 - 1642

¨ Astronomer & Physicist

¨ Struggled against the church to have his ideas accepted

They locked me up for this?

Falling Objects & gravitational pull

¨ Galileo experimented with ramps and dropping things to find that all objects fall at the same rate.

Acceleration due to gravity 9.8 m/s2 or 9.8 m/s/s

Galileo and Constant Acceleration

The inclined plane experiment

Galileo’s Projectile experimenthttp://www.youtube.com/watch?v=YavMnCmlFAU

Galileo worked out that there was a force acting in the opposite direction to motion and that if this force was decreased (by using oil, grease etc) then the object in motion would move further before stopping.

From this Galileo was to formulate his Law of Inertia

Unbalanced Forces!

Sir Isaac Newton 1642 - 1727

English mathematician

Built on Galileo’s work

1st Law of Motion

An object will keep the same motion unless acted on by an unbalanced force

2nd Law of Motion¨ The force of an object depends on the

mass of the object multiplied by the acceleration Sometimes, F = ma

3rd Law of Motion

¨ Every action force has a equal and opposite reaction force.