The History of Motion

ARISTOTLE (384-328BCE)

• Greek Philosopher

ARISTOTLE (384-328BCE)

• Used 2 models to explain motion: one for objects on Earth, one for the movement of the stars and planets

• Aristotle believed that everything on Earth is made of 4 elements and all objects behave according to the rules of their element.– Things float, fall, or rise to return to its proper

elemental place.– An object can be forced to move in directions other

than their natural motion, but when the force stops, so does the motion.

ARISTOTLE (384-328BCE)

• He concluded that a constant force will yield a constant speed.

• This idea remained unchallenged for nearly 2000 years!!!

JEAN BURIDAN (1300-1358)

• French Philosopher

JEAN BURIDAN (1300-1358)

• Believed that objects stayed in motion because they possessed “impetus”

• “Impetus”= an internal drive that makes them continue to move

GALILEO GALILEI (1564-1642)

• Italian physicist, mathematician, astronomer, philosopher

GALILEO GALILEI (1564-1642)

• The Greeks did not test the explanations based on their models

• Galileo designed experiments, made careful observations and analyzed his results.

• Scientists continue to study problems in a similar manner.

GALILEO GALILEI (1564-1642)

• Galileo conducted a 3 part motion experiment

• His experimental results challenged the previous beliefs:

According to Galileo, an object’s movement remains unchanged when no force resists the movement.– Galileo was defining “inertia”

NEWTON (1642-1727)

• English physicist, mathematician, astronomer, philosopher, alchemist, theologian

NEWTON (1642-1727)

• Experienced a moment of inspiration when he saw an apple fall from a tree…

• Aristotle had believed that the Earth and cosmos were distinctly different. Newton realized it was all one universe, operating under the same laws!!

NEWTON (1642-1727)

• Newton’s work revolutionized math and science

• He published his laws of motion and gravity in 1687 in a book known as the Principia

• He also studied light, developed the reflecting telescope, and invented calculus.

NEWTON’s Laws of Motion

• LAW #1

Inertia

Objects tend to remain in their current state of motion:

• Objects in motion will stay in motion

• Objects at rest will stay at rest

(unless acted upon by a net external force)

NEWTON’s Laws of Motion

• LAW #2

Fnet = ma

The net external force acting on an object will be equal to the object’s mass

multiplied by its acceleration

NEWTON’s Laws of Motion

• LAW #3

Action-Reaction

Every action force has an equal but opposite reaction force