Energy

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Energy

• Jayne Robinson
• Biloxi High School
• 2006

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5-1 Energy Work

• Kinetic and Potential Energy
• Energy cant be smelled or heard, but you can
  smell, see, and hear the effects of energy.
  Therefore, energy is the ability to cause change.
• Energy has many forms radiant, electrical,
  chemical, thermal, and nuclear.
• The basic unit of energy is the joule (J), named
  for the British scientist James Prescott Joule.

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Kinetic Potential Energy

• Kinetic energy is energy in the form of motion.
  KE depends upon the mass and velocity of the
  moving object. The greater the mass or the
  greater the velocity, the greater the KE,
  assuming the other component remains the same.
• Potential energy is stored energy. The amount of
  PE depends on its position and condition.
• Gravitation PE depends on height.
• Chemical PE is stored in foods and fuels.

4
Work

• Work is the transfer of energy through motion.
  In order for work to occur, a force must be
  exerted through a distance. Work depends on
• the amount of force exerted
• the distance over which the force is applied
• When force is applied in the direction of motion,
  work can be calculated W F x d
• Work Force x distance
• Work is measured in Joules
• 1 Joule 1 Newtonmeter
• Solve Practice Problems 1 2 page 113

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Work continued

• There are two factors that determine if work is
  being done
• something has to move
• motion must be in the direction of the applied
  force
• (even when you carry books across a level floor
  no work is done on the books b/c the force is
  holding the books up and the movement is
  horizontal)

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Conservation of Energy

• As many objects move, energy changes from kinetic
  to potential back to kinetic energy. Mechanical
  energy is the total amount of kinetic and
  potential energy in a system.
• In any given situation, energy may change from
  one form to another, but the total amount of
  energy remains constant energy is conserved.
• The law of conservation of energy states that
  energy may change form but it cannot be created
  or destroyed under ordinary conditions.

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Conservation of Energy continued

• Even as objects move, they eventually slow down
  and stop. Where does the energy go?
• Friction and air resistance are constantly
  acting on moving objects. These forces cause
  some mechanical energy to be changed to thermal
  energy or heat.
• Mechanical energy can be changed to thermal
  energy.

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5-2 Temperature and Heat

• Hot and cold are commons terms used to describe
  the temperature of materials. Are hot and cold
  definite? No, but, hot and cold are relative
  terms, they compare the temperature of two
  objects.
• All objects are made of matter and these
  particles of matter are in constant motion.
  Since moving objects have KE, the faster they
  move the more KE they have.

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Temperature and Heat

• Temperature is a measure of the average KE of the
  particles in a sample of matter.
• As the particles in matter move faster, their
  average KE increases, therefore the temperature
  increases.
• As the particles in matter move more slowly,
  their average KE decreases, and their temperature
  decreases.

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Thermal Energy

• Thermal energy is the total energy of the
  particles in a material, the total KE and PE in
  the material.
• The KE is due to vibrations and movement of the
  particles of material.
• The PE is determined by forces that act within or
  between the particles.
• The more mass a material has at the same
  temperature, the greater its thermal energy.
• Different kinds of matter have different thermal
  energies, due mainly to the ways the particles
  are arranged.

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Heat

• Energy flows from warmer objects to cooler
  objects. Heat is the energy that flows from
  higher temperature objects to lower temp objects.
  (It never moves from cool to warm.)
• Heat is measured in Joules since it is a form of
  energy and involves the transfer of energy.

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5-3 Energy from the Oceans Earth

• Scientists are always searching for new energy
  and heat sources. Two possible sources
• Ocean waters - the temperature change between the
  surface and deeper waters can be up to 15C.
  This causes the waters to constantly move and
  churn. This movement can be used to generate
  electricity.
• Magma - is the molten rock that lies deep beneath
  Earths surface. Wells could be drilled to use
  this heat to generate electricity.
• Both methods are expensive and could damage the
  environment. Study continues.

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5-4 Measuring Thermal Energy

• Different materials need different amounts of
  heat to produce similar changes in their
  temperatures. The materials have different
  specific heats.
• Specific heat (Cp) is the amount of energy it
  takes to raise the temperature of 1 kg of the
  material 1 degree Kelvin.
• Specific heat is measured in J/kgK (Joules
  per kilogram per degree Kelvin)
• Specific heat depends on the chemical makeup of
  the substances.

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Using Specific Heat

• Objects with high specific heats can absorb a lot
  of energy with little change in temperature.
• Water and alcohol have high specific heat
• Objects with lower specific heats change
  temperature more quickly as they absorb heat.
• Specific heat can be used to measure changes in
  thermal energy using the formula
• Q m x ?T x Cp ?T Tfinal - Tinitial
• change in thermal energy
• mass x change in temp x specific heat
• When ?T is positive, temp increased, when
  ?T is negative, temp decreased.

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• Solve Practice Problems 1 2 page 127
• Even though different substances have different
  specific heats, the mass and shapes of the
  substances also help determine the thermal energy
  characteristics - how the thermal energy moves.
• Solve equal amounts of iron, water, and sand,
  all at the same temp, were placed in an oven and
  heated. Using Table 5-1, pg 125, which has a
  final temp of 31C?
  5 C? 46 C?