History of Motion
and
Newton’s Laws of Motion
Centuries before
Isaac Newton's
discoveries, Polynesian
mathmatician Pao Lau
would have discovered
the laws of gravity
first..........had he
ever come out of the
coma.
Key Words
• Force – a push or a
pull on an object (unit
= Newton)
History of Motion
• Greeks – established
that forces cause
motion
Aristotle
• Natural motion – resting places
• Violent motion – imposed motion
• Earth didn’t move (natural motion)
but the heavens (stars) operated on a
model of perpetual motion.
Copernicus
• Earth moved around
the sun
Galileo
• Established that forces ARE NOT
needed to keep objects in motion.
• Came up with the idea of inertia
• Inertia – The tendency of an object to
resist a change in motion.
• Inertia depends upon only its mass
• Also recognized the
concept of frame of
reference.
Newton
• Developed 3 laws
of motion
• Developed the Law
of Universal
Gravitation
Newton’s First Law
• Unless acted upon by an
unbalanced force, an
object will maintain a
constant velocity
(direction and speed).
• Law of Inertia
Example:
st
1
Law
Newton’s Second Law
• Acceleration of an object
equals the net force on that
object divided by its mass.
• a = ∑F/m or ∑F = m a
• F (unit is Newton)
• Newton = kg x m/s2
• m (unit is kg)
• a (unit is m/s2)
Example:
nd
2
Law
• Which accelerates more
when the same amount of
force is applied?
What kind of
relationship is
between a & m?
What would the
graph look like?
Example:
• If dropped
from the
same height,
which would
have more
force when it
hit the
ground?
nd
2
Law
What kind of
relationship is
between m &
f?
nd
2
Law and gravity
• Reminder: acceleration of
an object due to gravity on
earth is 9.80 m/s2
• Weight is the force of
gravity on the mass of an
object.
• Mass is constant, weight
changes with gravity
nd
2
Law and gravity
Newton’s Third Law
• All forces come in pairs
that are equal in
magnitude (size) and
opposite in direction.
Characteristics of
rd
3 Law
• Always in pairs
• Equal in strength
• Opposite in direction
• Occur at the same time
• DON’T act on the same
object (that’s why they
don’t cancel)
Example:
rd
3
Law
• Action = ball hits bat
• Reaction = bat hits ball
(with the same amount of
force)
Example:
rd
3
Law
• Action = Tire pushes on
the road
• Reaction = road pushes on
the tire
nd
2
Newton’s
Law
Formulas
F = ma
W = mg
a = g sin θ
1 lb = 4.448 N
Vf = Vi + at
d = Vi t + ½ at2
2ad = Vf2 – Vi2
d = Vf + Vi t
2
or
d = ½
Vf + Vi
t