# NEWTON'S LAWS

Document Sample

```					NEWTON’S LAWS
FORCE
• Force: The push or pull on an object
• Net Force: The overall force on an
object
• Unbalanced force: When there is a
net force that causes acceleration
• Balanced forces: Equal forces acting
in opposite directions that will not
change an objects motion
Examples of Force

A flag being blown by the force of the
wind.

A jet engine propelling an airplane
forward.
MODELING FORCE
UNBALANCED FORCES

BALANCED FORCES
MODELING FORCE

UNBALANCED FORCES IN THE
SAME DIRECTION
PICTURING BALANCED FORCES
PICTURING UNBALANCED
FORCES
Friction
• The force that one surface exerts on
another when the two objects rub
against each other
• Friction acts in a direction opposite
the object’s direction of motion.
• Without friction an object would
continue to move at a constant
speed forever
Factors and Friction
• The strength of friction depends on
two factors
–The type of surfaces involved
–How hard the surfaces push
together
• Rough surfaces produce greater
friction than smother surfaces
Sliding Friction

• Sliding friction - when two solid
surfaces slide over each other.
• A snowboarder slides over the snow
covered slopes using sliding friction
everyday.
Rolling Friction

• Rolling friction - when an object
rolls over a surface.
• Skate boarders take advantage of this
type of friction all the time. Reducing
the amount of friction between the
surface and the wheels allow skaters to
go really fast.
Fluid Friction

• Fluid friction - when an object
moves through a fluid.
• This is how a surfer glides over the water
or a shark glides through the water. This
type is called fluid friction.
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 some outside
force
Inertia
• Inertia is the resistance to change in
motion
• EXAMPLE: If a car stops suddenly
inertia causes you to continue
moving forward. In order for
change in motion to occur a force is
required, such as a seat belt or the
windshield
Mass
• The amount of matter in an object
• EXAMPLE: A jar of pennies has
more mass than a jar of feathers
• The amount of inertia on an object
depends on the objects mass
• The greater the mass, the greater
its inertia
NEWTON’S SECOND LAW OF
MOTION
• The net force of an object is equal
to the product of its acceleration
and mass
• FORCE = MASS x
ACCELERATION
• UNITS = kg • m/s² =NEWTON (N)
PRACTICE THE SECOND
LAW
• A 53kg water-skier is being pulled by a
speedboat. The force causes her to
accelerate at 2m/s². Calculate the force.
• Force = mass x acceleration
• Force = 52kg x 2m/s²
• Force = 104 N
LETS PRACTICE AGAIN
• What force is needed to accelerate
an object with a mass of 25000
grams at a rate of 10 m/s2?
• Convert grams to kilograms
– 25000 g = 25 kg
• Force = 25 kg x 10 m/s2
• Force = 250 N
LET’S TRY ANOTHER ONE

• What is the force on a 1,000 kg
elevator accelerating at 2 m/s²?
• Force = 1000kg x 2 m/s²
• Force = 2000 N
SOLVING FOR ACCELERATION
• You can use force to find
acceleration
• Acceleration = force/mass
• You can increase acceleration by
change force
• Increase force = increase acceleration
• Increase mass = decrease
acceleration
LETS FIND ACCELERATION

• A 825N force is exerted on a 55kg
cart. Find the carts acceleration.
• Acceleration = force/mass
• Acceleration = 825N / 55kg
• Acceleration = 15 m/s²
NEWTON’S THIRD LAW OF
MOTION
• For every action there is an
equal but opposite reaction
Example of the   3rd   Law
Momentum

• Momentum is the product of its
mass and velocity
• The more momentum an object has
the harder it is to stop
• Momentum = mass x velocity
• Unit = kg • m/s
Let’s Practice
• Which has more momentum: a 3kg
sledgehammer swung at 1.5 m/s or a 4
kg sledgehammer swung at 0.9 m/s
• Momentum = mass x veloctity
Momentum1 = 3 kg x 1.5 m/s
• Momentum1 = 4.5 kg•m/s
Momentum2 = 4 kg x 0.9 m/s
• Momentum2 = 3.6 kg•m/s
Conservation of Momentum

• Lw of Conservation of Momentum
states that the total momentum of
the objects that interact does not
change.
• The total momentum remains the
same unless acted upon by an
outside force
Momentum- 2 moving objects
• When a car bumps into another
car that is going slower, it
transfers its momentum into the
other car.
• The car that got bumped is now
going faster, while the car that hit
it is going slower
Momentum- 1 object moving

• If a moving objects hits a
nonmoving object all the
momentum is transferred. The
nonmoving object begins to
move and the moving object
stops.
Gravity

• Gravity-The force that pulls
objects towards to Earth.
• Free fall: When gravity is the only
force acting on an object
–Objects in free fall accelerate as
they move towards the Earth.
Terminal Velocity

• Terminal Velocity is the
greatest velocity an object can
reach will falling
Gravity
• Near the Earth’s surface the rate of
acceleration due to gravity is 9.8 m/s²
–This does not take into account
friction
• All objects will accelerate down at the
same rate regardless of mass
–A brick and a feather will hit the
ground at the same time if it were
inside an airless chamber (vacuum)
Projectile versus free fall
• An object thrown and an object
dropped will both free fall at a rate
of 9.8 m/s²
• The will both hit the ground at the
same time
• Example: Shot a bullet and drop a
bullet at the same time it would land
at the same time.
Air Resistance

• Air resistance: Objects falling
through the air experience this
fluid friction
• Air resistance pushes the object
up as it falls causing it to slow
down
Air Resistance and Mass
• Air resistance is not the same for all
objects
• -A feather will fall slower then a rock
because of air resistance
• Air resistance increase as the velocity of
the object increases.
• Eventually air resistance will equal the
force of gravity and an object could stop
falling
Weight

• Weight is the force of gravity
on a person or object at the
surface of a planet
• Weight = mass X acceleration
due to gravity
• Weight = mass x 9.8m/s²
Do the Math - weight

• What is the weight of a person with
a mass of 75kg
• Weight = mass x acceleration due
to gravity
• Weight = 75kg x 9.8 m/s²
• Weight = 735N
Law of Universal Gravition
• The law of universal gravitation
states that the force of gravity acts
between all objects in the universe
• Any two objects in the universe
without exception attract each other
• We cannot tell most of the time
because the force is small

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 0 posted: 3/30/2013 language: Unknown pages: 37