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