1 / 21

Energy

This text explains the concepts of energy, work, and efficiency in mechanical systems. It covers topics such as potential energy, kinetic energy, how doubling or tripling speed affects stopping distance, energy conservation, pendulum energy, roller coaster energy, and the efficiency of machines.

maxwellj
Download Presentation

Energy

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

  2. Work • Work = (Force in direction of motion)*distance • W, Joule (J) = N-m • 1 J is work done in lifting 1 N (weight of average apple) at a constant speed, vertically 1 m

  3. Power • Power = Work/time • P, J/s = Watt • 1 horsepower = 746 Watts

  4. Potential Energy • Energy of position • Gravitational Potential Energy • PE = mgh • PE is the work done against the field to move an object to a certain position • Lifting apple 1 m – 1 J of PE • PE is the work that the object can do • Stored energy

  5. Elastic Potential Energy • Energy stored by compressing or stretching a spring • PE = 0.5 k x2 • K is the spring constant – a measure of the stiffness of the spring

  6. Kinetic Energy • KE is energy of motion • KE = 0.5 mv2 • Apple (0.10 kg) thrown at 5 m/s • KE = (0.5)(0.10 kg)(5 m/s)2 = 1.25 J

  7. Work = Energy • Work produces a change in energy • Work done by friction in stopping a car is equal to the change in kinetic energy experienced by the car • F*d = -0.5mv2 • How does doubling a car’s speed, affect the stopping distance?

  8. Stopping Distance • Given that F is a fixed value for given road/tire conditions, the stopping distance is proportional to the KE • How does doubling the speed affect the KE?

  9. Stopping Distance • Given that F is a fixed value for given road/tire conditions, the stopping distance is proportional to the KE • How does doubling the speed affect the KE? • (2v)2 = 4v2 • 4X the KE, thus, 4X the stopping distance

  10. Stopping Distance • How does tripling the speed affect the stopping distance?

  11. Stopping Distance • How does tripling the speed affect the stopping distance? • (3v)2 = 9v2 • 9X KE means 9X the stopping distance

  12. Energy Conservation • The total mechanical energy of an isolated system is constant. • That is, the sum of the PE + KE = constant • If PE decreases, KE increases … and vice versa • When gravity is the only unbalanced force, this is the case (conservative force)

  13. Pendulum Energy

  14. Roller Coaster Energy • First hill must be highest • What impact does friction have on the height of the successive hills?

  15. Machines • If no friction, then • Work Input = Work Output • Inclined plane • Pulley • Lever

  16. Inclined Plane • Output work = work done if you didn’t use the machine • Output work = (weight of load)(vertical height) • Input work = work done using machine • Input work = (force exerted)(length of plane)

  17. Pulley • Mechanical Advantage of Single Pulley is 1

  18. Lever

  19. Mechanical Advantage • Ideal Mechanical Advantage

  20. Efficiency • Because of friction, • work output < work input • Efficiency < 100%

More Related