NEWTON'S LAWS

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					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

				
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