Transcript All About Newton

Who was Isaac Newton?
Sir Isaac Newton (1643-1727), an
English scientist and mathematician
famous for his discovery of the law of
gravity, also discovered the three
laws of motion. He published them in
his book Mathematic Principles of
Natural Philosophy in 1687. Today
these laws are known as Newton’s
Laws of Motion and describe the
motion of all objects we experience in
our everyday lives.
Newton’s First Law States:
“An object at rest will remain at rest,
and an object in motion will remain in
motion unless acted upon by an
outside force.”
What does this mean?
• Basically, an object will “keep doing what it’s
doing” unless it is acted on by an unbalanced
force.
• If the object was sitting still, it will remain
stationary. If it was moving at a constant velocity,
it will keep moving.
• It takes force to change
the motion of an object.
What is Force?
• Force is any push or pull which causes
something to move or change its speed or
direction
• Forces can be balanced or unbalanced
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What is a Balanced Force?
• Balanced forces are equal in size and
opposite in direction
• They result in no change in velocity
What is an Unbalanced Force?
• Unbalanced forces are not equal and
opposite in direction.
• They result in a change in motion of the
object.
Some Examples from Real Life
• A soccer ball is sitting at
rest. It takes an
unbalanced force of a kick
to change its motion.
• Two teams are playing tug
of war. They are both
exerting equal force on the
rope in opposite directions.
This balanced force results
in no change of motion.
Newton’s First Law is also
called the Law of Inertia
• Inertia is the tendency of an
object to resist changes in its
state of motion.
• The First Law states that all
objects have inertia. The more
mass an object has, the more
inertia it has (and the harder it is
to change its motion).
• Mass is the measure of the
amount of matter in an object;
It is measured in Kilograms.
More Examples from Real Life
A powerful locomotive begins to pull a
long line of boxcars that were sitting
at rest. Since the boxcars are so
massive, they have a great deal of
inertia and it takes a large force to
change their motion. Once they are
moving, it takes a large force to stop
them.
On your way to school, a bug flies
into your windshield. Since the bug
is so small, it has very little inertia
and exerts a very small force on
your car (so small that you don’t
even feel it).
Newton’s First Law
• Don’t let this be you. Wear seat belts.
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• Because of inertia, objects (including you) resist
changes in their motion. When the car going 60
m/hour is stopped by the brick wall, your body
keeps moving at 60 m/hour.
If objects in motion tend to stay in motion, why
don’t moving objects keep moving forever?
•
•
•
Things don’t keep moving forever
because there’s almost always an
unbalanced force acting upon it.
A book sliding across a table
slows down and stops because of
the force of friction.
If you throw a ball upwards it will
eventually slow down and fall
because of the force of gravity.
What is Friction?
• Friction is a force that opposes motion
between 2 surfaces.
• The amount of friction depends on the:
• types of surfaces
• force between
the surfaces
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What is Air Resistance?
• Air can create friction and cause a moving
object to slow down. This is called air
resistance.
• Air resistance is the force of air exerted on
a falling object. The air pushes up as
gravity pulls down. It is dependent upon
the shape and surface area of the object.
• In the absence of air resistance, all objects
will fall at the same rate due to gravity.
What is Gravity?
• Gravity is an attraction force
between all masses.
According to Newton, every
object in the universe exerts a
gravitational attraction to all
other objects in the universe.
• The amount of gravitational
force depends upon the mass
of the objects and the distance
between the objects.
What is Gravity?
• The greater the mass….
• the greater the force of gravity….
• the greater the inertia the object is said
to have.
• Who experiences more gravity - the
astronaut or the lumberjack?
• The lumberjack!
• Which exerts more gravity on the
astronaut- the Earth or the moon?
• The Earth!
less distance
= more gravity
more mass =
more gravity
In outer space, away from gravity and
any sources of friction, a rocket ship
launched with a certain speed and
direction would keep going in that
same direction and at that same speed
forever.
Comprehension Check
• Ben and Jerry are arguing in the cafeteria. Ben says that if he
throws ice cream with a greater speed, it will have a greater
inertia. Jerry argues that inertia doesn’t depend on an objects
speed, but upon its mass. Why do you agree with and why?
• Imagine that you are in space, far away from Earth. If you
were to throw a rock, will the rock gradually stop or continue
in motion in the same direction and speed? Explain why.
• Lori Lostalot is being chased through the woods by a grizzly
bear. The large mass of the bear is intimidating, but Lori
believes she can use the bear’s mass to her advantage.
Instead of running in a straight line, she makes a zigzag
pattern through the woods. Explain why her plan will work
and help her to escape from the bear.