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When two surfaces rub the irregularities of one surface get

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When two surfaces rub the irregularities of one surface get Powered By Docstoc
					          True or False


   When two surfaces rub, the
irregularities of one surface get
  caught on those of the other
             surface.
True
What is friction?
 Friction is the force that two
 surfaces exert on each other
when the two rub against each
              other.
Friction acts in a direction __ to
the objects direction of motion.
Opposite
 The strength of the force of
friction depends on what two
           factors?
 The types of surfaces involved
and how hard the surfaces push
           together.
How is friction involved in
  sledding and skiing?
   There is very little friction
between a sled or skis and the
  snow because the snow is
      relatively smooth.

Also, the snow may be partially
melted, and fluid friction is much
      easier to overcome.
 Why does some friction occur
with seemingly smooth surfaces?
Even surfaces that seem smooth
 have irregular bumps that you
could see with a microscope, so
    friction occurs even with
    smooth-looking objects.
      Which kind of friction?




Friction occurs when an object
moves through a liquid or gas
Fluid friction
      Which kind of friction?




  Friction occurs when solid
surfaces slide over each other
Sliding friction
      Which kind of friction?




Friction occurs when an object
       rolls over a surface
Rolling friction
     Which kind of friction?




Friction occurs when objects
       are not moving
Static friction
Which kind of friction requires
more force to overcome, rolling
  friction or sliding friction?
Sliding friction
What kind of friction occurs when
moving parts have ball bearings?
Rolling friction
   How does oil between
machine parts reduce friction?
The oil keeps the machine parts
 from making direct contact, and
there is fluid friction between the
  parts instead of sliding friction.
   A force that pulls objects
toward each other is called __.
gravity
         True or False


The force that makes an apple
 fall to the ground is the same
force that keeps Earth orbiting
              the sun.
True
 The force of attraction between
two objects varies with what two
            factors?
Mass and distance between
       the objects.
How is weight different from
          mass?
Weight is a measure of the force
 of gravity on an object, while
mass is a measure of the amount
  of matter that makes up an
             object.
Weight is usually measured in
             __.
newtons
          True or False



On the moon, your mass would
 be less than it is on Earth, but
your weight would be the same.
False
When is an object said to be
        in free fall?
An object is in free fall when the
only force acting on the object is
             gravity.
Near the surface of Earth, what is
the acceleration of an object due
     to the force of gravity?
9.8 m/s2
   Objects falling through air
experience a type of fluid friction
           called __.
Air resistance
The greatest velocity a falling
 object reaches is called __.
Terminal velocity
         True or False



The greater the surface area of
 an object, the greater the air
         resistance.
True
An object that is thrown is
     called a(n) __.
projectile
          True or False


An object that is dropped will hit
the ground before an object that
 is thrown horizontally from the
          same height.
False
Draw arrows that show
the forces acting on the
     falling coconut.

 Label each arrow with
the NAME of the force.

				
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