Force push or pull

							          _____ – push or ____
• Sometimes ______
    forces are obvious but
    not always
•   can cause the ______
    of an object to
    change
•   force of moving ball
    causes ball at rest to
    move in the _______
    of the force
Forces
   • ___ force – 2 or more
       forces acting on a
       object @ same ____
   •   zero because the ___
       forces cancel each
       other
   •   Forces ____ in size &
       _______ in direction –
       balanced forces
               ________ forces
• 2 students pushing with
    ________ forces in
    opposite directions – net
    force occurs in the
    direction of the _______
    force
•   net force – will be the
    __________ between the
    two forces because they
    are in opposite ________
Unbalanced forces
         • forces are combined
             (______ together)
             because they are
             exerted on the box in
             the _______ direction
         •   net force that acts on
             this box – found by
             _______ the two
             forces together
Inertia – tendency of an object to
_______ any change in its motion
• If object is _______, it will have uniform
  motion
• It will keep moving at the same _____ &
  in same ________ unless acted on by an
  unbalanced force
• velocity of the object remains _______
  unless a force changes it
• object at ______ remains at rest
                   Inertia

• inertia of an object is related to its mass –
  greater the ____ of object the greater its
  inertia
• Sir Isaac ______ – stated rules that
  describe the effects of forces on the
  _______ of objects – known as Newton's
  law's of motion
Newton’s ______ Law of Motion

• Also called the law of _______
• states that an object moving at a constant
  velocity keeps moving at that _______
  unless acted on by an unbalanced net
  force
• object at rest stays at ____ unless acted
  on by an unbalanced net force
law of inertia – explains what
happens in a car crash
• A car traveling about
  50 km/h collides
  head-on with
  something solid, the
  car crumples, slows
  down, and stops in
  about 0.1 s
law of inertia – explains what
happens in a car crash
• Any passenger not wearing a safety belt
  continues to move _______ at the same
  speed the car was traveling
• Within about 0.02 s after the car stops,
  unbelted passengers slam into the
  dashboard, steering wheel, windshield, or
  the backs of the front seats
law of inertia – explains what
happens in a car crash
• force needed to slow a person from 50
  km/h to zero in 0.1 s is equal to 14 times
  the force that gravity exerts on the person
• belt loosens a little as it restrains the
  person, increasing the time it takes to
  slow the person down
• this reduces force exerted on the person
• safety belt also prevents the person from
  being thrown out of the car