Mfe chapter 4 notes
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  • 1. Work, Power, and Simple Machines Work Power Machines Simple and Compound Machines
  • 2. Work Work is defined as a force acting through a distance. Work=Force x Distance W=Fd=Newtons x meters=N- m=Joule A Joule (J) is an amount of work or energy that is equivalent to applying a 1 Newton force to an object for a distance of 1 meter. Energy is the ability to do work.
  • 3. Work (continued)Work= Force (F) x Distance (x)
  • 4. Power Power is the rate at which work is done. Power=Work/Time P=W/t=Joule/s=Watt 1 Kilowatt (kW)= 1000 Watts
  • 5. MachinesA machine is a device that makes work easier. Work input is the work that is put into the machine (the input distance times the input or effort force). Work output is the work that a machine does (the output distance times the output or resistant force).
  • 6. Machines (continued) Machines make work easier by changing the input force or distance or by changing the direction of input force. Work is conserved. Theoretically, the work put into a machine must equal the work that comes out of a machine. In practice this never happens due to energy being lost to friction.
  • 7. Machines (continued)A comparison of input work to output work is called efficiency. The efficiency of a machine is equal to work output/work input. Due to friction, no machine is 100% efficient. Machines with the smallest amount of friction are the most efficient.
  • 8. Machines (continued) The mechanical advantage of a machine is also important to know. Mechanical advantage tells how many times the input force is multiplied. The greater the mechanical advantage, the less force is required to do the work. This comes at the cost of distance, however.
  • 9. Simple Machines Allmachines are either one or more simple machine. There are 6 simple machines: Inclined plane, wedge, screw, lever, pulley, and wheel and axle.
  • 10. Simple Machines (continued) An inclined plane is a flat, sloped surface like a ramp. The longer the inclined plane is, the less force is needed to raise the object because of the decreased slope. Therefore, longer inclined planes with less slope yield greater mechanical advantages.
  • 11. Simple Machines (continued)
  • 12. Simple Machines (continued)A wedge is a moving inclined plane. Many wedges are made from two inclined planes stuck together like an ax. The longer and thinner the wedge, the greater its mechanical advantage.
  • 13. Simple Machines (continued)
  • 14. Simple Machines (continued)A screw is an inclined plane wrapped around a central bar to form a spiral. A screw gets its mechanical advantage from the length of the inclined plane wrapped around it. The closer together the threads on a screw, the greater its mechanical advantage.
  • 15. Simple Machines (continued)
  • 16. Simple Machines (continued)A lever is a rigid bar that is free to pivot about a fixed point called a fulcrum. A good example is the see-saw.
  • 17. Simple Machines (continued)
  • 18. Simple Machines (continued) There are three classes of levers. A first class lever has a fulcrum in the middle. A second class lever has the resistance in the middle. A third class lever has the effort in the middle. Just remember FRE.
  • 19. Simple Machines (continued)
  • 20. Simple Machines (continued) Notice that different classes of levers change the direction of the input force. This can sometimes make work easier. The mechanical advantage of a lever is generated by changing the length of the force or effort arm relative to the resistant arm of the lever.
  • 21. Simple Machines (continued)A pulley is a rope, belt, or chain wrapped around a wheel. A fixed pulley can change the direction of input force. Pulleys can be combined in systems. The mechanical advantage of a moveable pulley system is equal to the number of lifting lines.
  • 22. Simple Machines (continued)A wheel and axle is a simple machine made from two circular objects of different sizes. The wheel is the larger of the two. The mechanical advantage of a wheel is generated by the difference in the radii.
  • 23. Compound MachinesA compound machine is a combination of two or more simple machines.