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Chapter 5

Chapter 5. Machines and Mechanical Systems. Forces in Machines. How do you move something that is too heavy to carry? How were the pyramids built? Simple machines are devices that make work easier

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Chapter 5

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  1. Chapter 5 Machines and Mechanical Systems

  2. Forces in Machines • How do you move something that is too heavy to carry? How were the pyramids built? • Simple machines are devices that make work easier • A complex machine, like a bicycle, is many simple machines that work together to perform a task. This is also called a mechanical system

  3. Machines, Cont. • A machine is a device that makes doing work easier – they can do this in 3 ways • Increase the force being applied – screwdriver • Increasing the distance over which the force is applied – ramp • Changing the direction of the applied force - pulley

  4. Machines Every machine has a input force and an output force The input force is what is put in to make the machines work (effort force) The output force is what the machine does (resistance force)

  5. Machines and energy Remember – Law of conservation of energy A machine can never put out more work than goes in Wout is never greater than Win Most of the time energy is actually lost due to friction Ideal Machine - Wout = Win

  6. Mechanical Advantage • Number of times larger the output (resistance) force is compared to the input (effort) force • How much the machine multiples the force • MA= Fr/Fe • Can also be calculated with distance • MA= de/dr • No units

  7. Simple Machines • An un-powered mechanical device, like a lever • Other examples: Pulley, Wheel and Axle, Gears, Inclined Plane, Screw, Wedge

  8. More Pictures

  9. Lever • Made up of the effort arm, the resistance arm, and the fulcrum • Examples: crowbar, hammer, scissors, see-saw, human arm, pliers, nutcracker, can opener • The arms rotate around the fulcrum • Three types, 1st class, 2nd class and 3rd class • MA= Effort arm/Resistance arm

  10. Classes of Levers

  11. Pulleys • A pulley system is also known as a block and tackle • Pulleys use tension (pulling) force (not pushing force– have you ever tried to push anything with a rope?) to make work easier • The more ropes you have, the less input (effort) force you have to put in • MA of a pulley is the number of ropes (don’t count the rope you pull unless it goes against gravity)

  12. Pulleys Three types of pulley Fixed – attached to something that does not move (flag pole) Moveable – one end of the rope is attached to something and the wheel is free to move (zip line) Block and tackle – a system of pulleys made up of fixed and moveable pulleys

  13. Pulleys Fixed Pulley Movable Pulley Block and Tackle

  14. Wheel and Axle Simple machine consisting of a shaft of axle attached to the center of a larger wheel so that the wheel and axle rotate together Doorknobs, faucet handles are examples Actually a modified lever MA= radius of the wheel in meters/radius of the axle in meters

  15. Wheel and Axle

  16. Inclined Plane A sloping surface that reduces the force required to do work Ex, ramp, winding mountain road MA= Length of slope/ heigth of slope

  17. The Screw Inclined plane wrapped around a cylindrical post Treads form a tiny ramp all the way to the tip Jar cap, screw

  18. The Wedge Inclined plane with two sloping sides Downwards force turns into horizontal force, splitting an object Knife, axe

  19. Compound Machines Several Simple machines that work together Can opener had a wheel and axle, lever and wedge

  20. Work • The transfer of energy when a force makes an object move • W= FD • Work is in Joules because it is a transfer of energy (Joules) • Work is only done if the Force and the distance are in the SAME direction

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