Intro to Physics

Work and Energy Unit

Chapter 9

Key Terms

Work—unit Joules / Power—unit Watts / Energy
Law of Conservation of Energy / Equations
W= Fd
P = W/t / Total Mechanical Energy equation
TME = KE + PE
Work-Energy Theorem / Dissipated Energy / Kinetic Energy
KE = ½ mv2
Mechanical vs. non-mechanical energy / Types of Potential Energy / Types of Kinetic Energy
Pendulum and Period / Gravitational PE
(GPE = mgh)
Chemical PE
Elastic PE / Law of conservation of energy
g-force / Centripetal force
Simple Machines
Efficiency / Lever family / Inclined plane family
Total work input / Lever (1st,2nd and 3rd class) / Ramp
Useful work output / Pulley (fixed and movable) / Wedge
Mechanical advantage / Wheel and axle / Screw
Idealized vs. Actual Mechanical Advantage / MA = din/dout or
MA = Fout/Fin / Efficiency = AMA/IMA or UWO/TWI

Types of Energy Problems to Solve

  1. Work
  2. Power
  3. Total Mechanical Energy
  4. Gravitational Potential Energy
  5. Kinetic Energy
  6. Efficiency
  7. Mechanical Advantage

Work, Power and Energy

Learning Objectives

  1. Define work and energy, and explain how they are related.
  2. Describe how energy is stored, transferred and used.
  3. Define total mechanical energy.
  4. What is the law of conservation of energy and how does the total mechanical energy equation illustrate the law of conservation of energy?
  5. Explain the difference between kinetic and potential energy.
  6. Know the three examples of potential energy learned in chapter 9.4.
  7. Give four forms of kinetic energy as learned in chapter 9.6.
  8. Define dissipated energy and its role in energy transfer. What is the difference between mechanical and non-mechanical energy? How do friction, air resistance, sound and vibrations influence total mechanical energy?
  9. How does a hydroelectric power station illustrate the transfer of energy?
  10. How does the Work-Energy Theorem describe the relationship between work and energy?
  11. Solve problems using the work equation identify SI units for each.
  12. Define power and solve problems using the power equation.
  13. Solve problems using the gravitational potential energy and kinetic energy equations.
  14. Use a pendulum to explain how work is done and energy is transferred.
  15. How does string length on a pendulum affect the period of its swing?
  16. Explain the law of conservation of energy.
  17. Explain…
  18. Why does a ball eventually stop bouncing?
  19. Why does a person on a swing eventually come to a stop?
  20. How does a diver illustrate the law of conservation of energy?
  21. How does a roller coaster illustrate the law of conservation of energy?
  22. How does a skier illustrate the law of conservation of energy?

Simple Machines, Mechanical Advantage and Efficiency

Learning Objectives

  1. Identify input force, output force, input distance, output distance, effort arm, and resistance arm.
  2. Calculate the mechanical advantage of ramps, pulleys and levers.
  3. Explain how a machine makes work easier.
  4. Explain why a machine does not reduce the work done on an object.
  5. Determine the mechanical advantage of a machine using the mechanical advantage equations.
  6. Determine the idealized mechanical advantage of a pulley system.
  7. Explain the difference between useful work output and total work input.
  8. Calculate the efficiency of a machine knowing useful and non-useful work and actual and ideal mechanical advantage.
  9. Explain why a machine is not 100% efficient.
  10. Know the two families of simple machines.
  11. Explain the differences between the three classes of lever.
  12. Explain the difference between a simple and a compound (or complex) machine.
  13. Understand that input is equivalent to effort, output is equivalent to resistance.