Transcript Newton`s Three Laws of Motion

Newton's Laws of
Motion
Isaac Newton
(17th century scientist)
Sir Isaac Newton
• Lived from 1642-1727 in England.
• He was a dedicated physicist and
mathematician, and is considered to be
one of the most brilliant scientists of all
time.
• He is most famous for his three laws of
motion and his universal law of
gravitation, but did much more.
Mass & Weight
• Mass is the amount of “stuff” or matter that
an object contains.
• Weight and Mass are different.
• Weight, or how much an object weighs,
depends on the amount of gravity acting
upon it.
– Ex. You weigh less on the moon then on Earth.
Weight on other worlds
Force
• A force is what we call a push or a pull,
or any action that has the ability to
change motion of an object.
• The metric unit used to describe force is
called the Newton (N).
One Newton is equal to:
1 Kg x 1 m/s/s
Thus, one Newton of force
causes a one kilogram object to
accelerate at a rate of one meter
per second squared.
Your weight in Newtons!!!
Newton’s First Law of Motion
• An object at rest will remain at rest, and an
object in motion will remain in motion
unless acted upon by an unbalanced force.
– When you roll a ball, why doesn’t it roll on
forever? FRICTION
– This concept is also
referred to as the
Law of Inertia
The Law of Inertia
Inertia
• Inertia is defined as the property of an
object to resist changing its state of motion.
• The amount of inertia that an object has
depends on the amount of mass that it has.
• The more massive the object is the harder it
is to move or stop.
Balanced and Unbalanced Forces
• The motion of all objects depends
on the total of all forces acting on
the object.
• We call the total of all forces the
net force.
Balanced and Unbalanced Forces
Concept Check:
Mac and Tosh are arguing in the
cafeteria. Mac says that if he flings
the Jell-O with a greater speed it
will have a greater inertia. Tosh
argues that inertia does not
depend upon speed, but rather
upon mass. Who do you agree
with? Explain why.
Concept Check:
Ben Tooclose is being chased through
the woods by a massive bull moose
which he was attempting to photograph.
If Ben makes a zigzag pattern through
the woods, he will be able to use the
large mass of the moose to his own
advantage. Explain this in terms of
inertia and Newton's first law of motion.
Concept Check:
Mr. Wegley spends most
Sunday afternoons at rest on
the sofa, watching pro
football games and
consuming large quantities
of food. What effect (if any)
does this practice have upon
his inertia? Explain.
Newton’s Second Law of Motion
• Newton’s second law relates the
applied force on an object, the mass of
an object and the acceleration.
• It states: F = M x A
• Another form of this equation says:
• A= ___
F
force causes acceleration
M
mass resists acceleration
Newton’s second law
•
There are three main ideas related to Newton’s
Second Law:
1. Acceleration is the result of unbalanced forces.
2. A larger force makes a proportionally larger
acceleration.
3. Acceleration is inversely proportional to mass.
Newton’s Third Law of Motion
• For every action there is an
equal and opposite reaction.
• If you push on something it
pushes back with the exact
same force.
• Forces come in
pairs
Newton’s Third Law of Motion
• Sometimes the reaction force is
noticeable and causes motion
– (ex – recoil from a gun)
• Sometimes it is more
subtle, but forces
ALWAYS act in pairs.
– (ex - sitting in a chair,
walking)
Solving Problems
• A woman with a
weight of 500
newtons is sitting on
a chair.
• Describe one actionreaction pair of
forces in this
situation.
Concept Check:
Explain the net force in
each graph
Videos
• Football and Hockey
• Newtons Three Laws