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Forces Powered By Docstoc
					Scientific Terms                 Common Terms and Expressions

Gravitational Force (Gravity)    Pull of Earth

Magnetic Force                   Magnetic pull; magnetic push

Electrical Force (Electricity)   Static cling; static electricity; force of
                                 an electric current; force of lightning
Mechanical Force                 Muscular Force; hurricane force;
                                 slapshot; punch
Frictional force (Friction)      Rubbing; abrasion; roughness; force
                                 of resistance
Tensile Force                    Tightening

Compressive force                Crush; squash; squeeze; press;
                                 pinch; grip
Rotational Force                 Twist; turn, wring, coil, twirl
All forces have 2 components:
  • Magnitude: the quantity of force
  • Direction: which way force is pushing/pulling

 Use arrows in diagrams
  • Top of arrow shows direction
  • Thickness shows magnitude

 Unit of measure = Newton         (N)
  • Named after Sir Isaac Newton
The forces     Force applied to hold rock up.

are equal in
and opposite
in direction.

                      Force of gravity
Mass  is a measure of the
amount of matter or material
in an object.

Weight  is a measure of how
strong the force of gravity is
between two objects.
 Ifyou hold a rock in your hand, Earth
  pulls the rock toward its centre, and the
  rock pulls Earth toward its centre.
  However, the rock’s mass is so small in
  comparison to the mass of Earth that
  when you let go of the rock, the rock
  moves much farther toward Earth than
  Earth moves toward the rock. In fact, it
  looks as though only the rock moves.
Earthexerts a force of 9.8 N for
 every kilogram of an object’s mass

The   force of gravity is 9.8 N/kg

The moon’s force of gravity is
 approx. 1/6 of Earth’s pull. So if you
 went to the moon, your mass would
 be the same but your weight would
 be 1/6 what it is now.
 To  pick up
  something you
  must overcome
  the force of
  gravity that is
  keeping it where
  it is.
 How much force
  do you need to
  apply to pick up a
  container of milk?
 Ifa litre of milk has a mass of about
 You would have to lift upward with 9.8
  N of force to pick it up! Input force

                          Load force
A spring scale is a device used to
 measure forces.
The object to be weighed is attached
 to the end of a helical spring.
How far the spring stretches (the
 tension on the spring) indicates the
 weight of the object
The tension is shown on a calibrated
 scale on the side.
 Groupings: Pairs
 Using a spring scale, estimate and
  measure forces needed to perform
  common everyday tasks.
 Create the following chart:

 Task Estimated Actual       Difference
          force      Force
Liftone of the standard masses in
 your hand and get a feel for how
 much force is needed to hold it up.
Now, lift the mass with a spring scale
 and record the force in your chart.
Repeat 2 – 3 times with different
 masses.                  APPROPRIATE
Be sure to select the most
 spring scale.
 Now  practice a simple task, such as lifting a
  pencil case, until you get a feel for the
  amount of force needed.
 Then estimate the amount of force needed
  to perform the task.
 Record the task, your estimate, and the
  actual force needed.
 Determine the difference.
 Repeat for 5 other common items (binder,
  water bottle, openning a drawer, etc.)
 You may need to use string to assist you.
One per pair:
 Completed     Chart:
     Be sure to include all the elements of a good data

 Answers   to Questions:
      1.Why was it important to lift the standard masses
 and                   use the spring scale before
 making estimates?
      2. Compare your early estimates with your last
 few.                  Which were more accurate?

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