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DYNAMICS Powered By Docstoc

The study of why objects move or
          don’t move.
What is the natural state of
  motion of an object?
         Aristotle Observed:
• All objects eventually come to a stop.
• Therefore he concluded the natural state
  of motion for an object, is for the object to
  be at rest.
• He Incorrectly concluded that the only way
  an object stays in motion is if it has a force
  acting on it.
• But, what is a force?
Force – A push or a pull caused by
  the interaction of two objects.
•   F = Force
•   Units: Newtons (N) or pounds (lb)
•   1lb = 4.45N
•   A force is a vector quantity – It has
    magnitude (value) and direction.
          Weight is a Force
• It is caused by the interaction between the
  earth and an object.
• It has a value and a direction (down).
• Objects have the same mass everywhere,
  they only have weight when they interact
  with a planet, like earth.
• A 150lb person has a weight of 668N.
      Copernicus Observed:
• The motion of the stars and planets.
• He concluded that the earth was in
  constant motion.
• This idea was highly controversial.
• People preferred to think the earth was the
  center of the universe.
• As a result he was persecuted and had to
  work in secret.
   Galileo devised experiments to
    discover the natural state of
• His experiments represent the birth of
  modern day science.
• He also suffered persecution for his
Galileo’s Experiments:
 A ball rolling down a ramp, rolls to the
 same height on a ramp across from it.
 He worked very hard to eliminate friction,
 but of course he never could completely.

ho                                        hf

 He changed the angle of the second
 ramp and observed the ball rolled further
 before reaching hf.

ho                                       hf

 He than imagined what would happen if
 the second ramp was flat. Hmmm?
 What would happen? (remember to
 neglect friction)

ho                                         hf

 The ball is trying to roll back to a place where
                       ho = h f
The ball would roll forever with a
     constant velocity!!!!!!
    Galileo’s experiments
  demolished the idea that a
force is necessary to keep an
        object moving.
 The natural state of motion for
an object is to be moving with a
 constant velocity, which could
             be zero.
 So an object at rest is just a
    specific example of an
    object with a constant
   Sir Isaac Newton was the next
     major player on the scene
• He was born on Christmas day, the year Galileo
• His work influenced today’s world at a
  monumental level.
• He developed three laws that describe the
  motion of everything.
• He very well may have been one of the most
  influential human beings to ever live.
• And you thought he was just some dumb guy
  who got hit on the head with an apple.

• The natural tendency of an object to resist
  a change in motion.
• Mass is a measure of inertia.
        Newtons 1st Law:

An object with constant velocity (which
could be zero) continues with constant
velocity (same speed and direction) unless
an unbalanced force acts on it.
       Newtons 2nd Law:
The sum of the forces on an object is
equal to the mass times the acceleration
of the object.

         F  ma
                  The sum of
         Newtons 3rd Law:
For every force (action), there is an equal and
opposite force (reaction).

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