Simple machines and efficiency

Types of machines A machine is a device that is used Gears Inclined Plane Lever Pulley Screw Simple Machine Wedge Wheel and Axle     A machine is a device that is used To make a job easier. In other words, the device allows you to use less force to complete a task.

Inclined plane       An inclined plane is a sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed. Examples: Staircase, Ramp, Bottom of a Bath Tub

Inclined plane

Lever       A lever is a straight rod or board that pivots on a point known as a fulcrum. The fulcrum can be moved depending on the weight of the object to be lifted or the force you wish to exert. Pushing down on one end of a lever results in the upward motion of the opposite end of the fulcrum. Examples : Door on Hinges, Seesaw, Hammer, Bottle openers

Levers Bicycle brakes Door handle

Levers are classified according to classes

Pulley        A wheel that usually has a groove around the outside edge. This groove is for a rope or belt to move around the pulley. Pulling down on the rope can lift an object attached to the rope. Work is made easier because pulling down on the rope is made easier due to gravity. Examples: Flag Pole, Crane, Mini-Blinds

Pulleys

Mechanical Advantage People use pulley systems to get a benefit called Mechanical advantage. They do not have to apply as much force to get the same amount of work done on an object. To determine MA of a pulley system, count the number of strings minus the one you are pulling down on.

Pulleys What is the MA of the system Above?

Pulleys

Screw      A modified inclined plane wrapped around a shaft or cylinder. This inclined plane allows the screw to move itself or to move an object or material surrounding it when rotated. Examples: Bolt, Spiral Staircase   Simple

Screw

Wedge        Two inclined planes joined back to back. Wedges are used to split things. Examples: Axe, Zipper, Knife, wood maul

Wedge

Wheel and Axle     A wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together. When the axle is turned, the wheel moves a greater distance than the axle, but less force is needed to move it. The axle moves a shorter distance, but it takes greater force to move it. Examples: Door Knob, Wagon, Toy Car , Ferris wheel

Wheel and Axle

Gears       Two toothed wheels fit together either directly or through a chain or belt so one wheel will turn the other. Some gears may have a screw or a toothed shaft in place of one of the wheels. A gear may also be a combination of toothed wheels that produces a certain speed (such as a bicycle's top gear which makes the bike go fast, and the low gear for slow speed.) Examples: Clock, Automobile, Drill

Gears

Compound Machines These are combinations of several simples machines joined to form a particular task.

Compound Machine

Compound Machines

Calculating Mechanical Advantage MA= Force out Force input MA= de distance of the effort dr distance of the resistance dr refers to how far the object moves de refers to how much you have to move or how much rope that you pull in for a pulley system

Example Using a pulley system a boy pulls on a rope with 10N of force and lifts a 50 N weight. What is the MA of the pulley system? MA= F out/ F in or 50N/10N MA = 5 There are no units for mechanical advantage. The higher the MA, the better the machine.

Example A girl pulls a rope attached to a pulley system a distance of 10 m to move a weight up 2 meters. What is the MA? De=10m Dr=2m MA= de/dr 10m/2m=5

Efficiency Machines are rated according to efficiency. No machine is 100 percent efficient because of friction.

Efficiency Terms Force of resistance = fr( usually the weight of the object) Force of effort=fe ( how much force you put in) Distance of the resistance=dr (how far the object moves) Distance of the effort= de ( how far you move or how much rope you pull in from a pulley system)

Efficiency Formulas (Work output/ work input) X 100 Work Out X 100 Fr X dr = fe X de

Ideal MA The ideal mechanical advantage (IMA), or theoretical mechanical advantage, is the mechanical advantage of an ideal machine. It is calculated using physics principles because no ideal machine actually exists. The IMA of a machine can be found with the following formula: IMA = de/dr DE equals the 'effort distance' (for a lever, the distance from the fulcrum to where the effort is applied) DR equals the resistance distance (for a lever, the distance from the fulcrum to where the resistance is encountered

Additional websites http://library.thinkquest.org/CR0210120/Mechanical%20Advantage.html http://www.youtube.com/watch?v=yfAdmRJDKIc

http://atlantis. coe. uh http://atlantis.coe.uh.edu/archive/science/science_lessons/scienceles1/finalhome.htm