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Newton nd Law of Motion

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					   Newton’s
Laws of Motion
                 Force
• A force is a push or a pull.
• Net force refers to what you get when you
  consider the total effect of all the forces acting
  on an object.
• If the forces on an object are equal and
  opposite, they are said to be balanced, and the
  object experiences no change in motion.
• If the forces are not equal and opposite, then
  the forces are unbalanced and the motion of
  the object changes.
      Acceleration
• Acceleration is any change in speed and/or
  direction (a change in velocity) over some
  period of time.
• A net force acting on an object causes it to
  accelerate.




                 Object accelerates
             Inertia
• It’s hard to change the motion of an
  object that has lots of inertia & it’s easy
  to change the motion of an object that
  has little inertia.
• Mass can be defined as the measure of
  an object’s inertia.
• The more mass an object has, the more
  inertia it has, and the harder it is to
  change its motion.
  Applying a larger net force to an
object results in a larger acceleration.


A soccer ball sitting at rest takes an
unbalanced force of a kick to change
             its motion.
              leads to


small force              small acceleration



              leads to


large force              large acceleration
If you apply equal net
 forces to two objects,
    the one with the
    smaller mass will
     accelerate more.
             leads to


small mass              large acceleration




             leads to

large mass              small acceleration
 If you want to cause two
  different objects to have
the same acceleration, the
object with the larger mass
will require a larger force.
              can lead
                 to

small force              same acceleration



              can lead
                 to

large force              same acceleration
       Newton’s                     2 nd


net force acting on       mass of    acceleration of
                      =
     an object             object        object


                      F = ma
 Those three letters, plus the equals sign, are a
  statement of Newton’s 2nd Law of Motion.
 Newton’s 3rd
Law of Motion
   Imagine you are in a football game.
  You line up facing your opponent, the
ball’s snapped, and the two of you crash
                 together.


   Who feels the force of the crash?
  Action & Reaction
• Newton was the first to realize that all forces
  occur in pairs.
  – There is no such thing as an isolated force existing
    by itself!
• Right now, gravity is pulling you down in your
  seat, but Newton’s 3rd Law says your seat is
  pushing up against you with equal force.
• You are not moving because there is a balanced
  force acting on you.
   – Gravity is pulling down, your seat is pushing
     up.
  Newton’s 3rd Law
• Whenever one object exerts a force
  on a second object, the second
  object exerts an equal and opposite
  force on the first object.
• Simply put –
  – For every action (force) there is an
    equal, but opposite, reaction.
               Review
• Newton’s 1st –
   – Inertia- an object will resist a change in its
     motion. (If not moving, it doesn’t want to
     move. If moving, it wants to keep moving in
     a straight line at a constant speed.)
• Newton’s 2nd –
   – F = ma
   – force is equal to mass times acceleration
• Newton’s 3rd –
   – For every action there is an equal and
     opposite reaction.

				
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