Transcript Newton`s First Law of Motion

Isaac Newton (1642-1727)
• Father died before he
was born
• Mother remarried &
left him with his
grandmother
• Went to Cambridge –
earned his keep by
working for other
students
Black Death – Great Plague
• University closed
down
• Newton returned home
• Began revolutionary
advances in optics,
mathematics, physics
& astronomy
Academic Life
• Became Lucasian
Professor at
Cambridge
• First worked on optics
• Equated falling apple
with “fall” of moon
towards Earth
• Explained science of
moving bodies
Sir Isaac Newton
• 1686 published
book- Principia
• Three laws that
relate force to
motion
• An object at rest
remains at rest
unless acted on by an
unbalanced force
• -object will not start
to move until a push
or pull is exerted on
it
• Ex- golf ball on tee
• An object in motion
remains in motion at
constant speed and in
a straight line unless
acted on by an
unbalanced force
• Ex-rocket ship in
space- forever!
• Objects on Earth
slow down & stop
moving due to
friction
• Ex- ball stops rolling
on grass
• Ex- skateboard stops
rolling on pavement
• Matter resists any change
in motion
• Tendency to resist change
called inertia
• Mass is a measure of
inertia
• Ex- Baseball= small mass
-easy to start and change
motion
• Ex- Dumpster= large mass
- hard to start and change
motion
Another
st
1
Law Example
• Part 1-Acceleration
Depends on Mass
• Acceleration decreases
as mass increases
• Acceleration increases
as mass decreases
• Ex- empty versus full
shopping cart
• Part 2: Acceleration
Depends on Force
• Acceleration increases as force
increases
Ex- large force=fastball pitch
Ex-small force= tapping golf ball
into hole
Acceleration always in direction
of force
To change direction, exert force
in direction you want to go.
• Relationship of
acceleration (a) to
mass (m) and
force (F)
• Units• a = m/s/s
• m= kg
• F=kg m/s/s (N)
Equation can be Rearranged
•
•
•
•
•
a = F/m
or
F= m X a
or
m=F/a
Newton’s
nd
2
Law & Falling
Objects
• Compare apple &
watermelon
• Larger weight
offset by greater
inertia
• Accelerations due
to gravity are same
for both
• Forces act in pairs
• Action force
exerted by one
object = reaction
force exerted by
2nd object, but in
opposite direction
3rd Law – Think pairs!
• Rocket & gases
• Push of gas
downwards =
push of rocket
upwards
3rd Law – Think pairs!
• Swimmer &
water
• Force of swimmer
pushing on water
= force of water
pushing back
• Property of
moving objects
• Depends on
object’s mass &
velocity
P=mXv
Greater momentum requires
more force to stop or change
object’s direction
Large Truck vs Small Car
Speeding vs Slow Car
Momentum is Conserved
When objects interact, they
may exchange momentum,
but total amount of
momentum stays the same
Bowling Balls & Pins
Wrong & Right Effects