Conceptual Physics

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Conceptual Physics Study Notes Questions Week
5Energy (Chap. 8)

• Work is donethat is, energy is usedwhenever a
  forces is exerted over a distance (p164) W Fd.
  What is the MKS unit of work (i.e. energy)?
• How much work is done on a 10kg mass, lifting it
  2 meters, at the surface of the earth (p165)?
• Energy is the ability to do work (p166). Power is
  the rate at which energy is expended (i.e. the
  rate at which work is done). What is the MKS unit
  for power.
• A non-active human expends about the same power
  as a 100 watt light bulb.
• 1 food Calorie equals 4184 joules of energy. A
  180 Calorie soft drink contains 753,000 joules
  of chemical energyenough energy to lift a 80kg
  person about 3000 feet. In comparison, the same
  amount of energy is used by the simple act of
  living for about 2 hours.) One pound of body fat
  contains 3500 Calories of chemical energyenough
  energy to sustain human life for about 40 hours.
• Energy falls into three basic categories
• energy bound up in rest mass (E mc2),
• kinetic energy (KE ½ mv2), and
• potential energy (PE)energy stored in force
  fieldsin its various forms chemical energy,
  gravitational energy, mechanical energy (eg. a
  wound spring), nuclear energy, electrical energy,
  etc
• Kinetic energy, KE, is energy stored in momentum
  (p169), BUT it is not the same as momentum.
  Momentum is preserved in collisions, but kinetic
  energy usually is not (it is lost as heat). In a
  perfectly elastic collision, for example, two gas
  atoms colliding, KE is preserved.
• KE and PE are constantly interchanging in
  day-to-day life (p172). But usually KE, in the
  form of thermal energy, is siphoned off whenever
  two objects interact.

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Conceptual Physics Study Notes Questions Week
5Relativity (Chap. 28)

• Your frame of reference is the physical
  surroundings from which you observe and measure
  the world around you. For the most part, you are
  stationary with respect to it. For example, the
  interior of an airliner at 35000 feet, traveling
  at 600 mph (relative to the ground), is
  stationary to youit is your frame of reference
  (p604).
• The principle of relativity every observer must
  experience the same natural laws (p606). For
  example, if you measure the speed of light in
  your airliner, you would measure the same speed
  as when you were on the ground as when you were
  traveling at 185,000 mile per second (99.5 the
  speed of light!). The speed of light in a vacuum,
  c, is the same in all frames of reference.
• Special relativity deals with frames of reference
  traveling at uniform motion relative to one
  another (p606). General relativity deals with any
  frame of reference, whether it is accelerating or
  not.
• The Lorentz factor, f, is a key factor in special
  relativity
• f sqrt( 1 v2/c2 ) 1
• If you observe an object traveling at a speed v
  relative to you
• The rate of time, R, on the object appears slowed
  to fR
• The length of the object, L, is foreshortened to
  fL
• The apparent mass of the object, M, is increased
  to M/f
• E mc2 ? there is a whole lot of energy bound up
  in mass. Energy can be released through nuclear
  reactions that convert some portion of subatomic
  mass into energy (p615).
• In general relativity, acceleration due to
  gravity is indistinguishable from an acceleration
  frame of reference (p615).
• Gravitational field bend space-time, which
  causes light rays to bend, and time to slow in
  intense G fields (p617).