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Work & Simple Machines

Work & Simple Machines. Review. Define / Describe WORK. Work is done when a force causes an object to move in the direction that the force is applied. The formula for work is: W = F X D If there is no movement, there is no work. Two things must happen for work to be done. What are they?.

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Work & Simple Machines

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  1. Work & Simple Machines Review

  2. Define / Describe WORK • Work is done when a force causes an object to move in the direction that the force is applied. • The formula for work is: W = F X D • If there is no movement, there is no work

  3. Two things must happen for work to be done. What are they? • A force must applied to an object • The object must move in the same direction as the force.

  4. What is Power? • Rate at which work is done • P=W/t or P=Fd/t • Units for Power – joule/sec or watt • Large unit of power – kilowatt (kw) = 1000 watts

  5. What is purpose of a machine?

  6. What is purpose of a machine? • To make work easier.

  7. How do machines make work easier? • They can change the amount of force • They can change the distance (Remember that Work = Force X Distance) • They can also change the direction MORE

  8. How do machines make work easier? Any change in the size of the force changes the distance. No machine can increase both force and distance. • Multiply force which decreases distance the load moves. • Multiply the distance which decreases force. • Or, they leave force and distance alone but change the direction in which the load moves.

  9. What is mechanical advantage? The number of times a machine multiplies the effort or input force. • If MA is greater than 1, the effort force is decreased & applied over a greater distance • If MA is less than 1, the effort distance is decreased & a greater effort force is applied • If MA = 1, the direction of the effort is changed

  10. Calculating Mechanical Advantage • Ideal MA – does not take friction into account • IMA = de/dr • effort distance divided by resistance distance • MA does not have units • Actual MA – takes friction into account • AMA = Fr/Fe • resistance force divided by effort force

  11. What are the 3 types of simple machines?

  12. What are the 3 types of simple machines? • There are three simple machines: • the lever, the pulley, and the inclined plane The wheel and axle, the wedge, and the screw are modifications of the three simple machines.

  13. What is a compound (or complex) machine? • A machine made up of two or more simple machines.

  14. Describe LEVER A simple machine made with a rigid bar free to pivot (move) around a fixed point called a fulcrum

  15. Describe the 3 types of levers:

  16. Describe the 3 types of levers: • A first class lever is like a teeter-totter or see-saw. One end will lift an object (child) up just as far as the other end is pushed down. • A second class lever is like a wheel barrow. The long handles of a wheel barrow are really the long arms of a lever. • A third class lever is like a fishing pole. When the pole is given a tug, one end stays still but the other end flips in the air catching the fish. MORE

  17. First Class Lever • the fulcrum is between the effort force and the resistance force • Changes direction of effort force (downward) • Ex. see-saw, screw driver used to open a can, hammer used to pull a nail • moving fulcrum closer to the resistance (load)increases the MA of the first class lever

  18. Second Class Lever the resistance force is between the effort force and the fulcrum Ex. Wheel barrow moving resistance (load) closer to the fulcrum and the effort force farther from the fulcrum increases the MA of the second class lever

  19. Third Class Lever the effort force is between the fulcrum and resistance force Ex. fishing pole, broom, baseball bat moving the effort force away from the fulcrum and closer to the resistance force (load) increases the MA MA is always less than 1; multiplies distance rather than force

  20. Describe PULLEYS A simple machine made with a rope, belt or chain wrapped around a grooved wheel. A pulley works two ways.

  21. Diagrams of Pulleys Fixed pulley: Movable Pulley:

  22. How does a pulley work? A pulley works two ways. It can change the direction of a force or it can change the amount of force.

  23. What are the types of pulleys? • Fixed pulley Does not multiply force. Changes the direction of the effort force. Mechanical advantage is equal to one. • Movable pulley Multiplies effort force but cannot change direction of the effort force. Mechanical advantage is the effort distance divided by the resistance distance. • Pulley system A combination of fixed and movable pulleys. Mechanical advantage is equal to the number of supporting ropes.

  24. How does a fixed pulley work? A fixed pulley changes the direction of the applied force. ( Ex. Raising a flag ) the effort force is downward IMA = 1

  25. How does a moveable pulley work? A movable pulley is attached to the object that is being moved. pulley moves along the rope effort force is upward multiplies effort force IMA = 2

  26. Pulley System (Block & Tackle) • a combination of fixed and movable pulleys • Increases MA • can multiply effort force and change the direction of the Fe

  27. IMA in Pulley Systems • can be calculated by counting the number of supporting rope sections • the section being pulled on is counted only when pulled up Fixed Pulley IMA =1 Movable Pulley IMA = 2 IMA =3 IMA =3 IMA =4

  28. What is an inclined plane? A simple machine with no moving parts. It is simply a straight slanted surface. ( Ex. a ramp.) de de dr dr Increasing the effort distance increases the MA (use a longer ramp)

  29. What is a wheel and axle? A wheel and axle is a modification of a pulley. A wheel is fixed to a axle. The wheel and axle must move together to be a simple machine. Sometimes the wheel has a crank or handle on it. Examples of wheel and axles include roller skates and doorknobs.

  30. Wheel & Axle • An axle (smaller cylinder) attached to a larger wheel that rotate together • Effort force is usually applied to the wheel (lower Fe over a longer distance) and is transferred to the axle which provides the larger Fr

  31. Mechanical Advantage of Wheel & Axle • de = radius of wheel • dr = radius of axle • To increase MA, increase the effort distance by increasing the size of the wheel

  32. What is a wedge? A modification of an inclined plane that moves . It is made of two inclined planes put together. Instead of the load being moved up an inclined plane, the inclined plane moves the load.

  33. What is a Screw A simple machine that is like an inclined plane. It is an inclined plane that wraps around a shaft. The closer together the threads on the screw, the longer the effort distance (or inclined plane). A longer inclined plane increases the mechanical advantage.

  34. How do machines redistribute work? Any change in the size of the force changes the distance. No machine can increase both force and distance. • Multiply force – use a smaller effort force over a longer effort distance • Multiply the distance – use a larger effort force over a smaller effort distance • Or, they change the direction in which the effort force is applied – pull down instead of lift up

  35. Work Input • The work you put into the machine • Wi = Fede OR Wi = Fidi • Fe is the force you apply to the machine • de is the distance over which you apply the effort force

  36. Work Output • The work the machine does on the resistance (object being moved) • Wo = FRdR OR Wo = Fodo • FR is the weight of the object • dR is the distance the machine moves the object

  37. Efficiency • •Efficiency is the ability to convert work input into actual work output. • no machine is perfect 100% • loss caused by friction • Heat energy is produced

  38. Output Work WO Wi • Efficiency = 100 Input Work Calculating Efficiency • Ideal machines would have 100% efficiency.

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