DYNAMICS

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					        DYNAMICS


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
               motion.
• His experiments represent the birth of
  modern day science.
• He also suffered persecution for his
  efforts.
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



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




ho                                       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
            velocity.
   Sir Isaac Newton was the next
     major player on the scene
• He was born on Christmas day, the year Galileo
  died.
• 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.
1642-1727
                  Inertia

• 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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posted:8/31/2012
language:English
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