Review Ch'14

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Review Ch.1-4

• Quiz 1 Wednesday

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Chapter 1

• About Science

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theory

• a synthesis of a large body of information.
• The criterion of a theory is not whether it is
  true or untrue, but rather whether it is useful
  or nonuseful.

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hypothesis

• 1. a possible explanation, a small theory.
• 2. something taken to be true for the purposes of
  argument or investigation.

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scientific hypothesis

• the criterion is
• that it is testable

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scientific facts

• are not immutable and absolute, but are generally
  in close agreement as measured by competent
  observers of the same phenomena.
• The observations must be testable.

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Chapter 2

• Newtons 1st Law of Motion
• Inertia

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Aristotle on Motion

• Two Categories
• natural motion - every object has its natural
  place and strives to get there.
• violent motion - pushing or pulling
• Objects need force to maintain motion.

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heavier objects

• Aristotle reasoned that heavier objects would
  fall faster than lighter objects.
• Galileo disproved this in his famous Leaning
  Tower ball drop.

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Galileos Inclined Planes

• Galileo believed that an object would move
  endlessly in a straight line if it were not
  interfered with.
• Aristotle argued that you must continue to push
  on something to keep it moving.

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Newtons 1st Law of Motion

• Every object continues in its state of rest, or
  of uniform motion in a straight line, unless it
  is compelled to change that state by forces
  impressed on it.

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Inertia

• the property of objects to resist changes in
  motion.
• measurement is called mass
• Scientific unit for mass is kilogram (kg)

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Net Force

• the summative action of forces acting on an
  object.
• forces have size and direction
• Scientific unit for force is newton (N)
• US customary unit is pound (lb)

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Examples of Calculating the Net Force
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1 lb 4.45 N
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Mechanical Equilibrium

• achieved when Fnet 0, which is the case of
  Newtons 1st Law
• object at rest and remains so, or,
• object moves without change in speed or
  direction.
• symbol for sum of forces is S .

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Examples of Mechanical Equilibrium Note how
similar these two situations are!
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You try it. What is the unknown tension? What is
the upper limit on the mans weight?
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Example of Mechanical Equilibrium and Newtons
1st Law.
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Does the mass of the books affect the amount of
protection she gets? Would a stiff but light box
of the same size protect her as much?
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Chapter 3

• Linear Motion

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Speed

• scalar
• average speed distance traveled divided by
  elapsed time

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Velocity

• Vector
• Velocity is speed in a given direction (velocity
  is a vector, speed is a scalar)
• vavg displacement divided by time

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Acceleration

• Measures how quickly velocity changes

• Note acceleration refers to decreases in
  speed, increases in speed, and/or changes in
  direction i.e. to changes in the state of motion
  --- from Newtons law, lurches

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Velocity and Displacement in Free Fall

• v gt
• d ½gt2

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Chapter 4

• Newtons 2nd Law of Motion

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0
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0
When a Net External Force acts on an object at
rest, the object will begin moving. If the
object is already moving, its motion will
change. The direction of the change of motion is
in the direction of the net force.
Example Motion Diagrams when the Net Force is not
zero.
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Friction

• Objects in contact like each other, i.e. they
  form a chemical bond.
• They resist being moved when in contact.
• These resistance forces are called frictional
  forces.

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Categories of Friction

• Sliding Friction exists when one object slides
  against a second object, e.g. box along floor.
• Static Friction exists when a force is applied
  to an object, but that force is not large enough
  to break the frictional bond.

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Mass and Weight

• Mass is the quantity of matter.
• Mass measures inertia.
• Mass is measured in kilograms (kg)
• Weight is the force on mass due to gravity.
• Weight is measured in newtons (N) or pounds (lb).
• Weight Mass
• 1 kg of mass has a weight of 2.2 lbs

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Free-Fall

• only force acting is weight
• no other forces act
• air drag is negligible in size
• Ex. A solid steel ball falling a short distance
  is in free-fall.
• Ex. A feather falling to floor is not in
  free-fall since air drag is very significant.

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Comparing Accelerations of Objects in Free Fall.

• Downward force is weight.
• a weight/mass
• but an object with twice the mass will have twice
  the weight
• so the accelerations are the same
• We call this acceleration g.
• g is about 10m/s/s downward.

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Non Free Fall

• Whenever air drag is significant compared to
  weight the object will fall with acceleration
  less than 10m/s/s.

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Terminal Speed/Velocity

• As objects speed up the air drag increases until
  it is equal in size to the objects weight.
• In this case the net force is zero and therefore
  a 0.
• a 0 means velocity no longer changes.
• This velocity is the terminal velocity.

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End