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Simple machines

Simple machines. 2/19/2010. Mechanical Efficiency. Mechanical efficiency tells you what percentage of work input gets converted into work output It is a comparison of a machine’s work output with the work input The work output can NEVER be greater than the work input

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Simple machines

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  1. Simple machines 2/19/2010

  2. Mechanical Efficiency • Mechanical efficiency tells you what percentage of work input gets converted into work output • It is a comparison of a machine’s work output with the work input • The work output can NEVER be greater than the work input • This is true because some of the work input is used to overcome friction

  3. There are 6 Simple Machines

  4. What do Simple Machines Do? • Simple machines make work easier because they change the size or direction of the input force • However, they do not change the amount of work required • When a machine changes the size of the force, the distance through which the force is exerted must also change

  5. Example • If you are loading a truck that is 1 m off of the ground with a chest that has a weight of 450 N, what is the amount of work required? • Now say you use an inclined plane and the amount of force required is reduced to 150 N, how far would you have to apply the force?

  6. Levers • A lever is a simple machine consisting of a bar that pivots at a fixed point • That fixed point is called a fulcrum

  7. 3 Types of Levers • There are 3 classes of levers based on the locations of the: • Fulcrum • Load • Input force • First Class Lever • The fulcrum is between the load and the input force • They always change the direction of the input force • Examples: hammer, sea saw, row boat

  8. 3 Types of Levers • Second Class Lever • The load is between the fulcrum and the input force • They allow for less force to be applied but do not change the direction of the force • Example: wheel barrow

  9. 3 Types of Levers • Third Class Levers • The input force is between the fulcrum and the load • Do not change the direction of the input force • Example: Hammer

  10. Incline Planes • An inclined plane is a simple machine that is a straight slanted surface • Example: a ramp, ladder • To determine the MA of an inclined plane you divide the length of the inclined plane by the height to which the load is lifted

  11. Wedges • A wedge is a double inclined plane that moves • When you move a wedge through a distance, it applies a force on an object • The longer and thinner the wedge is, the greater the mechanical advantage • That’s why axes and knives work better when you sharpen them - - because you are making the wedge thinner • MA = the length of the wedge divided by the thickness of the wedge at its greatest thickness

  12. Screws • A screw is an inclined plane that is wrapped in a spiral • The closer the threads on the screw are to each other, the greater mechanical advantage the screw has • Examples: screws and lids

  13. Which One Would Have the Most Mechanical Advantage?

  14. Wheel and Axle • A wheel and axle is a simple machine consisting of two circular objects of different sizes • Examples: doorknob, ferris wheels, screwdrivers, and steering wheels

  15. Wheels • The MA of a wheel can be determined by dividing the radius of the entire wheel by the radius of the axle

  16. Pulleys • A pulley is a simple machine consisting of a grooved wheel that holds a rope or cable • A load is attached to one end of the rope and an input force is applied to the other end • There are 2 kinds: • Fixed • Movable

  17. Fixed pulleys • A fixed pulley is attached to something that does not move • A fixed pulley only changes the direction of a force • They do not increase nor decrease the amount of force • Therefore they have a MA of 1 • Input force and Output force are the SAME

  18. Movable Pulleys • Movable pulleys are attached to the object being moved • It does not change the direction of the force but they DO increase the amount of force • But there’s a trick: You must exert the input force over a greater distance that the load is moved

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