Ppt Work

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Ppt Work

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