Objective 1: Relate the Conservation of Energy to energy transformations

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Objective 1 Relate the Conservation of Energy to
energy transformations

• Describe how energy--mechanical, electrical,
  chemical, light, sound, and heat--can be
  transformed from one form to another
• Show understanding that energy transformations
  result in no net gain or loss of energy, but that
  in energy conversions less energy is available
  due to heat loss.

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Apply Conservation of Energy

• Apply the concept of conservation and
  transformation of energy within and between
  organisms and the environment--such as food
  chains, food webs, and energy pyramids
• Apply the concept of conservation and
  transformation of energy to other everyday
  phenomena.

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Objective 2 Relate waves to the transfer of
energy

• Relate wavelength to energy
• Relate frequency to energy
• Relate wavelength to frequency
• Describe how waves travel through different kinds
  of media
• Mechanical waves
• Water, Sound, Slinky, etc.
• Electromagnetic waves

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Describe how waves can be destructive /or
beneficial

• Describe how waves--earthquake waves, water
  waves, and electromagnetic waves--can be
  destructive (harmful) or beneficial (good) due to
  the transfer of energy
• Destruction (cons)
• Benefits (pros)

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ALL WAVES

• Transfer energy from one place to another
• Energy transferred does NOT have mass.
• Actual particles of the wave (such as water
  waves) are NOT transferred, but stay in the same
  place
• Have wavelength, frequency, amplitude
• SHORTER WAVELENGTH means HIGHER FREQUENCY AND
  ENERGY!

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Mechanical vs. Electromagnetic

• Require a medium, or something to travel through
  (cannot travel through space)
• Water waves, waves in a rope or slinky, and sound
  waves are examples

• Require NO medium, can travel through outer
  space!
• Examples of ELECTROMAGNETIC WAVES

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Electromagnetic waves, from low to high
frequency

• RADIO WAVES
• MICROWAVES
• INFRARED (HEAT)
• VISIBLE LIGHT
• ULTRAVIOLET
• X-RAYS,
• GAMMA RAYS

• LONG wavelength, LOW frequency AND energy
• HIGH wavelength, HIGH frequency AND energy

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VISIBLE LIGHT

• Only a SMALL band of the EM spectrum
• Regular white light can be separated into all
  the different colors with a prism
• This was discovered by Isaac Newton!
• RED (longest wavelength, lowest energy) to VIOLET
  (shortest wavelength, highest energy)
• ROY G BIV stands for Red, Orange, Yellow, Green,
  Blue, Indigo, Violet

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Longitudinal vs. Transverse

• Compression waves where one part of a medium
  smashes into another
• Wave particles travel parallel to the energy
• SOUND WAVES are longitudinal. They cannot travel
  in space because there is no medium

• Up and down waves, like wiggling a rope back and
  forth
• Wave particles travel perpendicular (at right
  angles) to the energy being transferred
• Electromagnetic waves are transverse!

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Electromagnetic vs Sound

• ALL travel at the speed of light, 186,000
  miles/second or 300,000,000 m/s
• Transverse
• Dont need a medium
• Can travel through outer space, all across the
  universe

• Travels MANY MANY times slower, only about 370
  m/s (almost a million times slower!)
• Longitudinal
• Require a medium
• Cannot travel through outer space
• Energy gets dispersed(spreads out) quickly

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ENERGY

• The ability to do work or make a CHANGE in
  something
• Energy has many forms, and all can be transformed
  from one to another
• There is a CONSTANT amount of energy in any given
  closed system, even in the universe as a whole!

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ENERGY AND WORK

• An ideal system means NO friction, and no
  energy lost as heat
• Energy is NEVER destroyed. It is only lost if
  it becomes unusable
• In an ideal system (or machine), you get ALL the
  energy OUT that you had to put IN. This is
  called 100 efficiency.
• There are NO ideal systems in real life!
• In REAL LIFE some energy is ALWAYS changed to
  lost heat because of friction!

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ENERGY AND WORK UNITS

• MASS is measured in kilograms kg
• WEIGHT and other FORCES are measured in NEWTONS
  N
• ENERGY is usually measured in Joules J
• WORK is usually measured in Newton-meters N m
• SINCE ENERGY AND WORK ARE EQUAL, A JOULE IS EQUAL
  TO A NEWTON-METER!

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POTENTIAL ENERGY

• This is STORED ENERGY
• Most commonly means GRAVITATIONAL potential
  energy, or energy stored because of a position
  HIGHER than some reference point (like the ground)

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Potential energy continued

• Can be ELASTIC OR SPRING potential energy, like
  the energy stored in a stretched rubber band, the
  spring in a wind up toy, or a drawn bow before
  shooting an arrow
• Potential energy is also stored in batteries, as
  CHEMICAL potential energy!

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POTENTIAL ENERGY continued

• POTENTIAL ENERGY can also be stored up in
  chemical bonds, such as in food or fat
• There is a tremendous amount of potential energy
  in MASS ITSELF, as Einstein showed with E mc2
• MASS itself is like VERY concentrated, congealed
  energy!
• Gravitational potential energy is described by PE
  mgh or mass x gravity x height

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KINETIC ENERGY

• Energy of motion (kine- means MOTION, like cinema
  means moving picture or movie!)
• KE 1/2 mass times velocity squared
• If something is NOT MOVING, is has ZERO KINETIC
  ENERGY!
• In an ideal system, ALL (or 100) of the WORK
  you put IN can be changed to KE
• In real machines, most energy is changed to heat.
  A car is only about 30 efficient! Only 30 of
  the gas gets changed to KE!

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POTENTIAL energy example

• If a rock has a mass of 5 kg, and it is on a hill
  2 m high, how much PE does it have?
• PE mgh or mass in kg x height in meters
• g 10 m/s/s
• Weight in Newtons mass in kg x gravity!
• PE weight in Newtons x height in meters
• so PE 5 kg (10 m/s/s) (2m) 100 Joules or 100
  J !

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PE Problems

• 1. If a rock has 5 kg of mass and is lifted up a
  1 m hill, how much PE does it have?
• 2. If a rock has has 20 N of weight and sits on
  top of a 2 meter tall box, how much potential
  energy does it have?

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PE Solutions

• 1. PE mgh
• so PE 5 kg x 10 m/s/s x 1 m 50 J
• 2. PE weight x height
• so PE 20 N x 2 meters 40 J
• Reminder Weight mass x gravity. For example,
  2 kg of mass X 10 m/s/s 20 N!

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Kinetic energy example

• KE 1/2 mass x velocity squared
• If a 3,000 kg car is traveling at 10 m/s, how
  much KE does it have?
• KE 1/2 (3,000 kg) (10 m/s)2
• 1,500 (100) 150,000 J!

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Kinetic energy problems

• 1. If a 60 kg girl is running at 5 m/s, how much
  Kinetic energy does she have?
• 2. If the girl stops and sits on a bench to rest,
  how much kinetic energy does she have?

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Kinetic energy solutions

• 1. KE 1/2 mv2
• so KE 1/2 (60 kg) (5 m/s)2
• so KE 30 (25) 750 J
• 2. KE 1/2 (60 kg) (0 m/s)2
• so KE 0
• She is not moving, so she has no Kinetic energy
  while sitting on the bench!

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Potential and Kinetic, transferred back and forth

• If you do 20 J of WORK lifting a rock onto a
  table, how much PE does the rock have?
• If the rock then falls off the table, how much
  KINETIC ENERGY does it have just before it hits
  the floor?
• WHERE did the rock GET the kinetic energy?
• When the rock smashes into the floor, where does
  the energy go?

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KE if you double mass

• If you had instead lifted a rock with TWICE as
  much mass, how much more WORK would you have put
  in to lift it?
• How much more PE would it have had at the top?
• How much more KE at the bottom?

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If you lifted more distance

• If, instead of lifting a rock with twice the
  mass, you lifted the SAME rock twice the height,
  how much more WORK would you have done?
• What if you lifted a rock with TWICE the MASS a
  distance TWICE AS FAR? How much more Work would
  you have to do?

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Roller Coaster

• ON a roller coaster, at what point is your
  POTENTIAL ENERGY greatest?
• Where is your KINETIC ENERGY greatest?
• Ignoring energy lost as heat due to friction,
  what can you say about the TOTAL amount of energy
  for the whole ride on the roller coaster?

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Roller Coaster continued

• As you go DOWN a hill on the ride,
• what kind of energy is being transferred to what
  other kind?
• As you go UP a hill on the ride,
• what kind of energy is being transferred to what
  other kind?

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Energy transferred

• How is energy transferred from the SUN, to you
  walking down the sidewalk?
• If you hit a baseball, describe the energy
  changes occurring.
• You throw a ball into the air. What energy
  transformations are taking place?

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MOMENTUM

• Momentum is mass X velocity
• p mv
• The unit is kg m/s

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The Law of Conservation of Momentum

• Momentum in a closed system is ALWAYS CONSERVED
• Momentum before an event is equal to momentum
  after an event in the system
• Classic examples are explosions, car crashes,
  pool balls, shooting a gun.

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Momentum conserved

• In a collision, if one pool ball collides into
  another one that is at rest, pool ball 1 shares
  some momentum with pool ball 2
• The TOTAL momentum of both pool balls added
  together is THE SAME before and after the
  collision
• p p
• m1v1 m2v2

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The Impulse Momentum Theorem

• CHANGE in momentum is EQUAL to Impulse
• IMPULSE is equal to IMPACT (or force) times the
  TIME INTERVAL of the impact
• ?p F?t or ?(mv) F ?t

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Applications

• Why is it better to bend your knees when you jump
  off a table?
• Why do you move your hand backward when catching
  a fast pitch?
• Why do air bags help?
• Why does a karate expert often try to have a
  SHORT time of impact?

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More applications

• If you only want maximum velocity, such as trying
  to achieve maximum range of a golf ball, you
  should hit the ball with
• a) a short time of impact
• b) a long time of impact
• c) it makes no difference

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Applications continued

• If a building is on fire and you want to minimize
  the force of impact on your bones when you jump
  from the 2nd story window, you should
• a) land with straight legs
• b) land on your feet but bend knees
• c) drop and roll to maximize time of impact