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Energy and Machines

Energy and Machines. Physical Science. What is Energy? . Is the ability to do work Two general types Kinetic Energy Potential Energy . Kinetic Energy. The energy of motion Depends on mass and speed Measured in Joules (J) Symbol = KE. Potential Energy.

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Energy and Machines

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  1. Energy and Machines Physical Science

  2. What is Energy? • Is the ability to do work • Two general types • Kinetic Energy • Potential Energy

  3. Kinetic Energy • The energy of motion • Depends on mass and speed • Measured in Joules (J) • Symbol = KE

  4. Potential Energy • Energy that is stored (not moving) • Based on position and height • Measured in Joules (J) • Symbol = PE

  5. Is it Kinetic or Potential Energy? • Rock sitting on the cliff’s edge • A car going down a hill • Sitting at the top of a slide • Going down a slide

  6. Calculating Kinetic Energy • Formula • KE = ½ m * v2 • KE= kinetic energy (J) • m= mass (kg) • v= velocity (m/s) Example Problem The cart on a roller coaster has a mass of 100 kg. It is going a speed of 6 m/s along the track. How much kinetic energy does it have?

  7. Calculating Potential Energy • Formula • PE = m * g* h • PE = potential energy (J) • m= mass (kg) • g= gravity (9.8) • h= height (m) Example Problems A 30 kg rock is sitting on a ledge 5 m from the ground of Earth. How much potential energy does it have?

  8. How to also write PE formula • PE = m*g*h • Weight • PE= Fgh

  9. Forms of Energy • Mechanical Energy • Motion and Position of everyday objects • Examples • Speeding trains • Bouncing balls • Thermal Energy • Total PE and KE of the particles in an object • Examples • Liquid metals

  10. Forms of Energy • Chemical Energy • Energy stored in chemical bonds • Examples • Chemical reactions • Burning coal • Electrical Energy • Energy associated with electric charges • Examples • CD players • Calculators

  11. Forms of Energy • Electromagnetic Energy • Form of energy that travels through space in the form of waves • Examples • X-rays • Visible Light • Nuclear Energy • Energy in atomic nuclei • Examples • Sun • Nuclear power plants

  12. Energy Conversion • Energy changing from one form to another • Examples • Kinetic to Potential • Mechanical to Thermal

  13. Law of Conservation of Energy • States: • Energy cannot be created nor destroyed, only changed • Meaning • Amount of energy at the start must equal amount of energy at the end

  14. Energy Conversion: Roller Coaster • PE Greatest • Conversion • PE decrease • KE increase • PE = KE • KE Greatest • Conversion • KE decrease • PE increase • KE = PE • PE Greatest

  15. Energy Conversion: Pendulum • PE Greatest • Conversion • PE decrease • KE increase • PE = KE • KE Greatest • Conversion • KE decrease • PE increase • KE = PE • PE Greatest

  16. Energy Conversion: Throwing Ball Up • KE Greatest • Conversion • PE increase • KE decrease • PE = KE • PE Greatest • Conversion • PE decrease • KE increase • KE = PE • KE Greatest

  17. Machines

  18. What is a Machine? • A device that makes doing work easier • Two divisions • Simple machines • Compound Machines

  19. How do Machines make work Easier? • Increase Force • (ex: car jacks) • Increase the distance a force is applied • (ex: using a ramp) • Changing the direction of an applied force • (ex: ax blade)

  20. Simple Machines • Machines that does work with only one movement of the machine

  21. Six types of Simple Machines 1). Lever A bar that is free to pivot or turn around a fixed point (ex: teeter totter) 2). Pulley Grooved wheel with a rope, chain, or cable running along the groove (ex: wishing well)

  22. Six types of Simple Machines 3). Wheel & Axle A shaft/axle attached to the center of a larger wheel so that both rotate together (ex: door knobs) 4). Inclined Plane A sloping surface (ex: ramp)

  23. Six types of Simple Machines 5). Screw An inclined plane wrapped in a spiral around a cylindrical post (ex: jar lids) 6). Wedge An inclined plane with one or two sloping sides (ex: knife)

  24. What are Compound Machines? • When two or more simple machines operate together • Example: Can Opener • Wheel & Axel • Level • Wedge

  25. Input force & Output force • Input Force • Force applied TO the machine • Symbol = Fin • Output Force • Force applied BY the machine • Symbol = Fout

  26. Input Work & Output Work • Input Work • Work done by you on a machine • Symbol = Win • Output Work • Work done by the machine • Symbol = Wout

  27. Input & Output Work: The Relationship • Input work equals Output work in an ideal machines • Win = Wout • Why? • Law of conservation of Energy • Energy is not created nor destroyed

  28. What is Mechanical Advantage? • Is the number of times that a machine increases an input force • Two Versions • Actual Mechanical Advantage (AMA) • Ideal Mechanical Advantage (IMA)

  29. Actual Mechanical Advantage • Determined by measuring the actual forces on a machines • Ratio of the output force to the input force

  30. Actual Mechanical Advantage Formula AMA = Fr / Fe (Big/Small) • AMA= actual mechanical advantage • Fr= resistance force (output force) • Fe=effort force (input force) • AMA has no unit • Fr & Fe has the unit of “N”

  31. AMA Formula Practice 1) What is the actual mechanical advantage of a machine who’s input force is 30-N but produces an output force of 90-N? 2) You test a machine and find that it exerts a force of 10 N for each 2 N of force you exert operating the machine. What is the actual mechanical advantage of the machine?

  32. Ideal Mechanical Advantage • Is the mechanical advantage in the absence of friction • Because friction is always present, the actual mechanical advantage of a machine is always less than the Ideal

  33. Ideal Mechanical Advantage Formula IMA = de / dr(Big/Small) • IMA = ideal mechanical advantage • de = displacement of effort force (input distance) • dr = displacement of resistant force (output distance) • IMA has no unit • de and dr has the unit of meters

  34. IMA Formula Practice 1) A woman drives a car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the IMA? 2) A construction worker moves a crowbar through a distance of 4 meters to lift a load 0.5 meter off the ground. What is the IMA of the crowbar?

  35. What is efficiency? % • The percentage of work input that becomes work output • Because there is always some friction, the efficiency of any machine is always less than 100 percent

  36. Efficiency Formula • Wout = work output (J) • Win = work input (J) • Small/Big x 100

  37. Efficiency Formula Practice 1) You have just designed a machine that used 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?

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