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Transcript

  • 1. Work & Machines
  • 2. What is work?
    • If you push or pull something, that is NOT work.
    • Work is the transfer of energy that happens when a force makes an object move .
    • Remember – force is a push or a pull on an object
    • Key - for work to be done, the object has to move .
  • 3. Doing Work
    • Two things have to happen in order to consider it work…
      • The object has to move
      • The motion of the object has to be in the direction the force was applied.
  • 4. Doing Work Example
    • The bell rings and you need the books under your desk.
    • Lifting up the book is doing work…why?
      • The books move and…
      • There is a force applied, by your arms, in the direction that the books move.
  • 5. Doing Work Example
    • Your arms are doing the work.
    • Now that they are in your hands, you start to walk with them…
    • It is now your legs that are doing the work to move you and your books, not your arms.
  • 6. Work and Energy
    • When work is done, energy is always transferred.
    • Think about carrying a box with your kid brother up the stairs. When you are done, your arms will be sore.
    • Remember – when you increase the height of an object you increase its potential energy.
  • 7. Work and Energy
    • So, by taking the box-n-brother up the stairs, you have increased its height, therefore, increasing its potential energy and you transferred energy to it.
  • 8. Work and Energy
    • Remember – Energy is the ability to cause change.
    • AKA – Energy is the ability to do work.
    • If something has energy, it can transfer energy to something else.
  • 9. Work and Energy
    • When you do work on something, you increase its energy.
    • IF you do work on something, you decrease your energy.
    • Energy is always transferred from the object that is doing the work to the object that has the work done on it.
  • 10. Calculating Work
    • Would you do more work if you lifted the books from the floor to your waist or from the floor to over your head?
    • Over your head…
    • You do more work when you exert a greater force and when you move an object a greater distance.
  • 11. Calculating Work
    • The amount of work done depends on two things.
      • The amount of force exerted
      • The distance the object is moved
  • 12. Calculating Work
    • When a force is exerted and an object moves in the direction of the force, the amount of work done can be calculated…
    • Work = Force x distance
    • W=Fd
  • 13. Calculating Work
    • If Maria applies a force of 25N to a baseball for a distance of .1m, how much work did she do?
    • W = ?
    • F = 25N
    • d = .1 m
    Remember - Newton x meter = Joule & Work is always measured in Joules
    • W=Fxd
    • W = 25 N x .1m
    • W = 2.5 J
  • 14. Calculating Work
    • Force is measured in
      • Newtons (N)
    • distance is measured in
      • meters (m)
    • Newton (N) times meters (m) = Joule
    • Work, like energy is measured in
      • Joules (J)
    • One joule is about the amount of work required to lift a baseball a vertical distance of 0.7m
  • 15. When is work done?
    • Push a book across a table a distance of 1m.
    • The distance you use to calculate the work you did is how far the book moved while the force is being applied , or while your hand is in touching the book.
    • The distance in the formula, W=Fd, is the distance that your hand was in contact with the book

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