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  • pg 1
            What is a force?
• A force is a PUSH or a PULL.
• Forces do not have mass nor do they
  occupy a space.
• Forces can
  – tear, bend, twist, or stretch an object.
  – Change the direction of the motion
• Measured in Newtons (N)
       2 main types of forces
• Contact forces
  – A force between two objects in direct contact
    with one another.
• Non-Contact forces
  – Forces that can act on objects at a distance
    and between two objects which are not in
    direct contact with one another.
          Gravitational Force
• Pulls objects towards the center of the earth
• Objects exert a force of attraction on all
  objects around it.
  – The force may be small that we can’t feel it.
• The larger the mass, the stronger the
  gravitational force
  – The sun’s gravitational force pulls smaller bodies
    towards it
• The closer the two objects are, the stronger
  the gravitational force
          Gravitational force
• Objects fall to the ground at the same rate,
  regardless of their mass in the absence of
• Overcoming gravity:
  – Energy is needed to overcome gravity
  – More energy if you’re going against it
  – Less energy if you’re going towards it.
Gravitational energy in our daily
            Frictional Force
• A force that opposes motion.
• Produced when two surfaces are in contact
  with each other
• Can cause an object to move slower
• More friction is exerted if the object’s mass is
• Surfaces play a role in the amount of friction
                      Frictional Force
• Types of friction
  – Sliding
     • Two solid objects with one object sliding over the other
     • snowboarding
  – Rolling
     • When a circular object rolls over a surface
     • cycling
  – Fluid
     • Involves a solid object moving through a wet or fluid (liquid or
     • Parachuting, wakeboarding
Infer the friction generated in the
           given pictures
           Frictional energy
• Energy is required to overcome friction.
• How much energy is needed to overcome
  friction over smoother surfaces?
• How much energy is needed to overcome
  friction over rougher surfaces?
• When is frictional energy beneficial? When
  is frictional energy harmful?
Frictional energy in our lives
             Magnetic Force
• A force of attraction that pulls unlike poles.
• A force of repulsion that pushes like poles.
• A MAGNET attracts magnetic materials,
  which include those made up of Iron, steel,
  cobalt and nickel
            Magnetic force
• A stronger magnet exerts a stronger force
  of attraction
  – The material may move faster
  – A stronger force is needed to overcome a
    stronger magnet

 N              S         N                    S
Magnetism in our daily lives
         The PENDULUM

           Metal ball

           The PENDULUM
• Found in clocks; has a weight and a string
• Air resistance (frictional force) and gravity
  affect the motion of the pendulum
• The length of the string also affects the
  time for the pendulum to complete its

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