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Kinetic and Potential energy

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					               Catalyst
• What is Newton’s 3rd Law? Give me an
  example of the law?
Kinetic and Potential energy

          Page 447
        Go over homework
• Pg 377 Data analysis
• Pg 377 questions 1-7
• Energy: the ability to do work
• work is a transfer of energy
• measured in Joules= kgm2/s2
             Kinetic Energy
• the energy of motion
• kinetic energy of any moving object
  depends upon its mass and speed
  – equation: Kinetic energy= half the mass times
    the velocity squared
          » KE= ½ mv2

http://www.brainpop.com/science/energy/kin
  eticenergy/preview.weml
          Practice Problem
• A 0.10 kg bird is flying at a constant speed
  of 8.0 m/s. What is the bird’s kinetic
  energy?
      More Practice Problems
•   A 20kg dog is running at a constant speed of
    16 m/s. What is the dog’s kinetic energy?
•   A 50 kg human is walking at a constant speed
    of 4 m/s. What is the human’s kinetic energy?
•   A human has a kinetic energy of 3.1 J, and a
    speed of 2.7m/s. What is the human’s mass?
•   A car has a kinetic energy of 6.3 J, and a
    speed of 5.4 m/s. What is the car’s mass?
           Potential Energy
• energy that is stored as a result of position
  or shape.

http://www.brainpop.com/science/energy/pot
  entialenergy/preview.weml
 Gravitational Potential Energy
• potential energy that depends upon an
  object’s height
• an object’s gravitational potential energy
  depends on its mass, its height, and the
  acceleration due to gravity.
  – Potential energy (PE) = mgh
  – g (on earth) = 9.8 m/s (N)
          Practice Problem
• Suppose the diver at the top of a 10.0
  meter high diving platform has a mass of
  50.0 kilograms. You can calculate her
  potential energy relative to the ground.
       More Practice Problems
•   A bird is sitting on top of a 17 meter high tree branch.
    The bird has a mass of 2 kg, what is its potential
    energy relative to the ground?
•   A jaguar is sitting on a tree branch 4.3 meters from the
    ground, waiting to attack its prey. The jaguar weighs
    89kg, what is its potential energy relative to the
    ground?
•   The potential energy for a 2.5 kg squirrel in the tree is
    1,500 J. At what height is the squirrel at?
•   The potential energy for a diver is 4,900 J. The diver is
    on top of a 15 meter high diving board. What is the
    mass of the diver?
      Other Forms of Energy
• Mechanical energy: energy associated
  with the motion and position of everyday
  objects
• the sum of the potential and kinetic
  energies
  – example: bouncing a ball, speeding trains etc
                Homework
• Create a comic strip that either discusses
  the differences between
  – Kinetic energy and potential energy (include
    equations)
  – Newton’s 3 laws of motion
• Thermal Energy:
• The total potential and kinetic energy of all
  the microscopic particles in an object.
  – example: when an object’s atoms move
    faster, it’s thermal energy increases and the
    object becomes warmer
      Elastic Potential Energy
• The potential energy of an object that is
  stretched or compressed
  – Normally springs back to its original state
• Chemical energy:
• energy stored in chemical bonds
  – burning gasoline
• Electrical energy:
• energy associated with electrical charge
  – ex flashlights, cds
• Electromagnetic energy:
• energy that travels through space in the
  form of waves
  – ex galaxies
• Nuclear energy:
• energy stored in atomic nuclei
  – nuclear fission or nuclear fusion



Practice problems:
• Questions 6-9 pg 452
              Exit Ticket
• Name and explain all of the energies
  needed to heat a cup of water
Conservation of energy

       Page 453
     Conservation of Energy
• Energy can be converted from one from to
  another
• Energy conversion: the process of
  changing energy from one form to another.
• The law of conservation of energy states
  that energy cannot be created or
  destroyed
• Gravitational potential energy of an object
  is converted to the kinetic energy of
  motion as the object falls
    Energy conservation Equations

•     Mechanical energy = KE + PE
•     (KE + PE)beginning = (KE + PE) end
•      KE beginning = PE end
•      PE beginning = KE end
          Practice Problem
• At a construction site, a 1.50 kg brick is
  dropped from rest and hits the ground at a
  speed of 26.0 m/s. Assuming air
  resistance can be ignored, calculate the
  gravitational potential energy of the brick
  before it was dropped
      More Practice Problems
• At a playground, a 3.4 kg ball is dropped from
  rest and hits the ground at a speed of 28 m/s.
  Assuming air resistance can be ignored,
  calculate the gravitational potential energy of the
  ball before it was dropped.
• At a hospital, a 1.8 kg stethoscope is dropped
  from rest and hits the ground at a speed of 14
  m/s. Assuming air resistance can be ignored,
  calculate the gravitational potential energy of the
  stethoscope before it was dropped.
• Einstein’s equation E = mc 2, says that
  energy and mass are equivalent and can
  be converted into each other. (c = speed
  of light 9 x 1013 J
•     energy is released as matter is
  destroyed, and matter can be created from
  energy.
         Practice Problems
• 9 and 10 on page 459.
       Finish Newton’s Laws
• Create a mini comic strip that explains and
  demonstrates
  – Newton’s 1st, 2nd, and 3rd laws

				
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posted:11/14/2011
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