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Work & Machines

Work & Machines. Topics. Work and Power Definition, Calculation, and Measurement Using Machines Nature of Machines Mechanical Advantage Efficiency of Machines Simple Machines. Work.

brenna-camacho
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Work & Machines

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  1. Work & Machines

  2. Topics • Work and Power • Definition, Calculation, and Measurement • Using Machines • Nature of Machines • Mechanical Advantage • Efficiency of Machines • Simple Machines

  3. Work • Definition: Work is the application of a force to an object that results in the movement of the object over a certain distance. • For work to occur, object must move • The motion of the object must be in the same direction as the applied force on the object • Work and energy are related. Energy is the ability to do work. Motion results when work is being done.

  4. Calculating Work • Work equals the product of a force (F) and the distance (d) over which the force is applied. • Work (W) = Force (F) x Distance (d) • SI Unit: Joules = kg x m2/s2

  5. Example • A mover pushes a box for 5 meters across the floor. He applies a force of 100N directly to the floor. How much work does he do?

  6. Power • Definition: Amount of work done in a certain amount of time; or Rate at which work is done. • Calculating Power: • Measured in watts (w) Work (Energy)time Power =

  7. Using Machines • What is Machine • Mechanical Advantage • Efficiency of Machine

  8. Using Machines • Definition of Machine – Device that makes work easier to do. • Machines increase applied force (input force) and/or change direction of applied force to make work easier. • Because W = Fd, therefore, increasing distance reduces the amount of force needed to do the work.

  9. Mechanical Advantage • Mechanical Advantage (MA) is the number of times a machine multiplies the input FORCE (NOT WORK). • Input Force(FI) – force applied to machine, aka, Effort Force • Output Force(FO) – force applied by machine to do the task or overcome resistance, aka, Resistance Force • When a machine takes a small input force and increases the magnitude (strength) of output force, a mechanical advantage is produced.

  10. Calculating MA • Example, if a machine increases an input force of 10N to an output force of 100N, the machine has a mechanical advantage of ( )??

  11. Efficiency in Machines • In machines, when talking about efficiency, it is WORK (NOT FORCE) • There are two types of WORK • Work Input(Win) = Work done by you on a machine. • Work Output(Wout) = Work done by the machine

  12. Ideal Machine • Win = Wout • But according to Conservation of Energy, no energy is created or lost. Therefore machines cannot create energy. • Wout is never greater than Win. • Some energy is transferred in the form of heat due to friction. • Lubricant can make machines more efficient by reducing friction

  13. Efficiency • Because the amount of work put into a machine is always greater than the amount of work done by the machine, machines are never 100 percent efficient. • Definition: Measure of how much of the work put into (Win) a machine is changed into useful output (Wout) by the machines

  14. Calculating Efficiency • Efficiency is a comparison between the work output and the work input of a machine. Work Output Work Input EfficiencyWork = X 100%

  15. Simple Machines • Definition: A machine that does work with only one movement. • To make work easier, simple machines change forces by: • Change the direction • Change the strength (magnitude) • Change both

  16. Types of Simple Machines • Lever • Inclined Plane • Wedge • Screw • Wheel and Axle • Gear • Pulley

  17. Lever • Definition: A bar that is free to pivot about a fixed point called fulcrum. • The bar may be straight or curved. • Three Parts: • Effort arm (Force) – part of lever where effort force is applied • Resistance arm (Load) – part of lever where resistance force is applied • Fulcrum – Support or balance

  18. Three Types of Lever • Depending on the location of the resistance arm (resistance force) and the effort arm (effort force) relative to the fulcrum, there are three types of lever:

  19. First-Class Lever • Definition: Fulcrum is located between the effort and resistance forces; effort being further than resistance; multiples and changes direction of force.

  20. Examples • Crowbars, scissors, pliers, seesaws.

  21. Second-class Lever • Resistance force is located between the effort force and fulcrum; always multiples force. • No change in direction of force. Greater MA is resulted when fulcrum is closer to the load

  22. Examples • Nutcrackers, wheel barrows, doors, and bottle openers

  23. Third-class Lever • Effort force is between resistance force and fulcrum; does NOT multiply force, but does increase distance over which force is applied. • Always produce a gain in speed and distance and a corresponding decrease in force.

  24. Examples • Tweezers, hammers, brooms, shovel, your arm

  25. Inclined Plane • Definition: A sloping surface that reduces the amount of force required to do work. • It is easier to move a weight from a lower to higher elevation

  26. MA of inclined plane is equal to the length of the slope divided by the height of the slope. • Less force is required if a ramp is longer and less steep

  27. Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work. A B C

  28. Wedge • Definition: Inclined plane with one or two sloping sides. If two sides, the planes are joined back to back. • Wedges are used to split things. • Examples: Axe, knife, your teeth, saw, doorstop

  29. Screw • Definitions: inclined plane wrapped in a spiral around a cylindrical post MA of an screw can be calculated by dividing the number of turns per inch.

  30. Screw • Three parts: head, shaft, and tip. • Head: part where you exert force • Shaft: has ridges called threads that wind around the screw. • Tip is usually sharp. • Uses: fasten things together. • Examples: jar lid, screws, drill bids

  31. Wheels and Axle • Definition: machine with two wheels of different size rotating together. • Consists of a large wheel rigidly secured to a smaller wheel or shaft called axle. • Example: doorknob,

  32. 5 1 MA of Wheel and Axle • The mechanical advantage of a wheel and axle is the ratio of the radius of the wheel to the radius of the axle

  33. Gear • Modified form of wheel and axle. • Each gear in a series reverses the direction of rotation of the previous gear. The smaller the gear will always turn faster than the larger. • Example: Can opener, bicycle, egg beater

  34. Pulley • Definition: Grooved wheel with a rope, simple chain, belt or cable running along the groove is a pulley.

  35. Types of Pulley • Fixed pulley is attached to something that doesn’t move. Force is not multiplied, but direction is changed. • Movable pulley has one end of the rope fixed and the wheel free to move; multiplies force. • Block and tackle (compound) system of pulleys of fixed and movable pulleys.

  36. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Force=Mass x Acceleration Force=10 x 2 Force=20 N Work=Force x Distance Work = 20 x 10 Work = 200 Joules Power = Work/Time Power = 200/5 Power = 40 watts

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