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Physical Science: Work


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Physical Science: Work

  1. 1. WorkChapter 5.1
  2. 2. What is work?• You work on math problems.• You go to work.• Making a sandwich is work.• Taking out the trash is too much work.• Doing your homework is work.• What machines help us work?
  3. 3. In physics, work is:• *Work is a formula: W=Fd• *W= Work; F= Force; d= distance• *Example:• *Moving an object with a force of one newton for a distance of one meter= one joule of work• *A joule is a unit that measures work
  4. 4. Force (N)Work (joules) W=Fxd Distance (m)
  5. 5. Brainstorm using a circle map:1. In the Center write: Work2. In the circle write types of simple machines3. In the frame of reference write down what work these machines do
  6. 6. Input and Output• *Input = how much force you put into doing work• *Output = how much work was done• *The work output can never exceed the work input!
  7. 7. Work:
  8. 8. Efficiency• *Efficiency is the fraction of incoming energy that goes into a process.Examples: Fuel mileage, appliances and energy efficiency
  9. 9. *Efficiency• What does it mean to be efficient?• *In a very efficient machine, all or most of the work input becomes work output• In other words…if five joules of work was used to lift a box, the box would move the equivalent of five joules output- nothing was wasted.
  10. 10. What about friction?• *In the real world- Work Output is always less than work input. – WHY?• *Forces like friction use up some of the input work – Example: wheel turning on an axle can get very hot…when the wheel gets hot some of that input work is being converted to heat.
  11. 11. Friction
  12. 12. *What is Power?• *Power is the rate at which work Work (joules) is done.Power (watts) P=W t Time (sec)
  13. 13. Power:
  14. 14. Power Demo• These two people did the same amount of work.•The difference is Power: One person used morePower and got the work done much faster•A more powerful machine does the same amountof work in less time
  15. 15. Review:• Work = Force x distance
  16. 16. Your Turn…• On your paper: – Look through Chapter 5, Section 1 Pg 85-90 – Add more information from this section into your notes. (at least six items)
  17. 17. Practice:• Skill Sheet 5-A Example:• How much work is done on a 10 N block that is lifted 5 meters off the ground by a pulley? Work = F x d W = 10N x 5 meters = 50 newton- meters OR 50 joules Remember: newton-meters = joules
  18. 18. Work• Work = Force x Distance• Work is only done when something is moved a distance in the direction of the force.