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Simple Machines

Simple Machines. What is a Simple Machine?. A simple machine is a device that helps to accomplish a task by redirecting or alleviating some of the work input required. Simple machines cannot create energy. They can only redistribute or produce force on an object.

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Simple Machines

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  1. Simple Machines

  2. What is a Simple Machine? • A simple machine is a device that helps to accomplish a task by redirecting or alleviating some of the work input required. • Simple machines cannot create energy. They can only redistribute or produce force on an object. • The six basic simple machines are the lever, the inclined plane, the wedge, the screw, the wheel, and the pulley. • Simple machines help people lift or move heavy objects, split thick solids, and secure things together.

  3. Levers • Lever: a long piece of wood, metal, etc. that rests on a turning point (fulcrum) to lift or open something • An object (load) is placed on one end, while a force pushes the other end down to move the object. • Force applied x Distance (between force and fulcrum) = Load x Distance (between load and fulcrum) • Examples: bottle openers, scissors, hammers (when pulling a nail out) Applied force   Lesser force (load)

  4. Lever Types • First Class Lever • Fulcrum is between force input and load. • Input (effort) and load forces are on opposite sides, but act in the same direction. • The closer the fulcrum is to the load, the less effort is needed. • Examples: see-saws, pliers, scissors • Second Class Lever • Load is between force and fulcrum. • Effort and load forces are on the same side of the fulcrum but act in opposite directions. • The closer the load is to the fulcrum, the less effort is needed. • Examples: staplers, nutcrackers

  5. More Lever Types • Third Class Lever • Force is between fulcrum and load. • Effort and load forces are on the same side, but act in opposite directions. • Effort required to lift the load is greater than the load. • Examples: fishing rods, tongs, brooms • For first and second class levers: large output of force is gained over a small distance (force multiplier) • For third class levers: small output of force is gained over a large distance (speed or distance multiplier)

  6. Pulleys • A pulley is a wheel and axle over which a rope or chain is pulled in order to lift or lower heavy objects. • Pulleys change the direction of motion/force applied to lift an object. • The amount of force required to move the object remains the same • Using a pulley feels easier because you are working with gravity by pulling down on the rope, as opposed to working against it by pulling the object straight up. < Without the use of a pulley, the required lifting force is 100lbs. With the use of a pulley, the required lifting force is still 100lbs. >

  7. Multiple Pulleys • Force required when using more than one pulley to pull up an object is less than force required when using one pulley to pull up the same object. • This is because the weight of an object is split by the number of pulleys you use. • However, the distance of the rope multiplies by the number of pulleys you use also. Two pulleys: force required is cut in half, rope length is increased.

  8. Inclined Planes • An inclined plane is a surface set at an angle against the horizontal. • Inclined planes split gravitational force in two: • Force parallel to plane • Force perpendicular to plane • Only parallel force must be counteracted when moving objects up a plane • Force required to do work is less than when pushing on a flat surface • Mechanical advantage = slope/length of plane • Used as ramps or sloping roads, and can be combined to form a wedge

  9. Wedges • Wedges consist of a pair of inclined planes set against each other. • By moving the planes relative to each other, a wedge builds up force in a direction perpendicular to the moving wedge. • Mechanical advantage = slope/thickness; The advantage gained requires corresponding increase in distance • Wedges are used to separate or hold objects. • Door stops, axes, and teeth are examples of commonly used wedges. Wedge used to hold a door Wedge used to separate an object

  10. Wheel and Axle • A wheel and axle is a simple machine made up of two circular objects of different sizes rotating on the same axis. • The wheel has the larger diameter, and turns about the smaller axle. • Because a wheel is basically a lever that can turn 360o, effort or resistance force can be applied anywhere on that surface. The central point of the wheel and axle serves as the fulcrum. • A force applied to the wheel is multiplied when it is transferred to the axle, which travels a shorter distance than the wheel. • Since the wheel is larger than the axle, it always moves through a greater distance than the axle.

  11. Use of the wheel and axle • The mechanical advantage (the number of times a machine multiplies the effort force) depends on the radius of the wheel and of the axle. • The wheel allows objects to roll along the ground, decreasing surface friction by substituting rolling friction for sliding friction. • The wheel can also be used to lift objects by wrapping a cord attached to a weight to the axle. It is less efficient than the lever at lifting objects. • Examples: screwdrivers, doorknobs, windmills, gears, Ferris wheels

  12. Screws • A screw is another type of an inclined plane. It is a helical inclined plane wrapped around a cylinder to form a spiral, with a wedge at its tip. • The main use of a screw is to hold objects together with its helical grooves. • A screw can convert a rotational force to a linear force and linear force to rotational force.

  13. Use of Screws • The screw’s ratio of threading determines its mechanical advantage. • Screws with wide grooves are harder to turn, yet travel a shorter distance to their destination. • Screws with narrow grooves are easy to turn, but have to be twisted over a greater spiral distance. • One example of the screw as a simple machine is Archimedes’ Screw - used to bring water up from low sources to the location of use by passing through a helix. • Other examples of screws include bottle caps, worm gears, drills, wrenches, jacks, and light bulbs.

  14. Simple and Compound Machines • A compound machine is composed of multiple simple machines working together to redirect or apply force. • While a simple machine has only one motion, complex machines may have two or more. • Examples of compound machines are a wheelbarrow, which uses a lever and a wheel and axle to redirect pushing force, and a bicycle, which redirects force from the user’s feet through pulleys to turn the wheels and propel the user forward.

  15. Works Cited • http://www.uark.edu/depts/aeedhp/agscience/simpmach.htm • http://www.enchantedlearning.com/physics/machines/Levers.shtml • http://www.simplemachines.info/netscape.htm • http://www.howstuffworks.com/pulley.htm?printable=1 • http://www.sciencebyjones.com/simple_machines.htm • http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machines/sciber/intro.htm • http://www.mos.org/sln/Leonardo/InventorsToolbox.html

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