Transcript Aristotle`s Classification of Motion

Aristotle’s Classification of Motion
• Greek scientist
(Born 384 BCE)
• Classified motion
into two categories
– Natural motion
– Unnatural motion
• Natural motion
occurs without
force.
• Unnatural motion
required a force.
Aristotle’s Classification of Motion
• Aristotle believed that
– The speed at which an object falls is directly
related to the mass of an object.
– Motion continues so long as there is only an
applied motion (force) to an object. Removing the
motion (force) stops the object.
• Aristotle’s ideas lasted almost 2000 years…
• It would take a man named Galileo to start
the wheels of change in this field of
knowledge called physics.
Galileo’s Concept of Inertia
• Galileo Galilei was
an Italian scientist
(1564-1642 CE).
• Believed in
experimentation
• Blew away
Aristotle’s notions
of motion
Galileo’s Concept of Inertia
• Galileo found that
–Except for the effects of friction,
objects fall at the same rate…
regardless of size.
–Force is required to start an
object moving, but not to keep it
moving.
Galileo’s Concept of Inertia
• The tendency of things is to remain as they are…
– If moving, they tend to keep moving.
– If at rest, they tend to stay at rest.
• This is called inertia.
• Another inertia definition: The ability of an object
to resist motion...
Concept Check
A ball rolling on a pool table slowly comes to a stop.
• How would Aristotle explain this behavior?
• How would Galileo explain it?
• How would you explain it?
Galileo Formulates Speed &
Velocity
• Until Galileo motion was described as
either fast or slow.
• Galileo measured speed by considering
distance and the time it took to cover it.
Speed =
Galileo Formulates Speed &
Velocity
• Velocity differs from speed in that we
also know the direction of the moving
object.
• Velocity is both speed and direction
(therefore, it is a “vector quantity”).
• Constant speed doesn’t mean constant
velocity… the opposite is true though.
Concept Check
• What is the average speed of
cheetah that sprints 100m in
4s?
• The speedometer on a bicycle
moving east reads 50 km/h. It
passes another bicycle moving
west at 50 km/h. Do both bikes
have the same speed? Do they
have the same velocity?
• “She moves at a constant
speed in a constant direction.”
Say the same sentence in fewer
words.
Motion is Relative
• Everything is always moving!
• Our speed relative to the sun is 30
km/s.
• Discussing motion
always involves a
reference point.
Assignment
• History of Motion Questions &
Speed Worksheet
–Answer in complete sentences
–Use your own sheet of paper