1 / 37

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.

gerek
Télécharger la présentation

Energy and Machines

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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?

More Related