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Published byJemima Golden Modified over 9 years ago
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Simple Machines and Work
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What is a Simple Machine? A simple machine has few or no moving parts. Simple machines make “work” easier
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Wheels and Axles The wheel and axle are a simple machine The axle is a rod that goes through the wheel which allows the wheel to turn Gears are a form of wheels and axles
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Pulleys Pulley are wheels and axles with a groove around the outside A pulley needs a rope, chain or belt around the groove to make it do work
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Inclined Planes An inclined plane is a flat surface that is higher on one end Inclined planes make the work of moving things easier
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Wedges Two inclined planes joined back to back. Wedges are used to split things.
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Screws A screw is an inclined plane wrapped around a shaft or cylinder. The inclined plane allows the screw to move itself when rotated.
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Levers A lever is a simple machine containing a bar that can turn around a fixed point Fixed point is called a fulcrum There are three classes of levers
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Levers The force the person applies to the machine is called effort force The object to be lifted, the load, is called the resistance. The force the machine uses to move the resistance is called the resistance force The force the machine exerts is greater than the force the person exerts, SO using a machine makes a person’s job easier!
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Levers-First Class In a first class lever the fulcrum is in the middle and the load and effort is on either side Think of a see-saw
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Levers-Second Class In a second class lever the fulcrum is at the end, with the load in the middle Think of a wheelbarrow
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Levers-Third Class In a third class lever the fulcrum is again at the end, but the effort is in the middle Think of a pair of tweezers
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Simple Machines and Work Energy cannot be created or destroyed; and, because energy is the ability to do work, work cannot be created either No simple machine can do more work than the person using it supplies Machines can increase or change the direction of the force a person exerts; and, some machines allow a person to use less force to do the same amount of work
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Simple Machines and Work The amount of work a person puts into a machine is called the work input Work input equals the person’s effort force multiplied by the distance of that effort work input = fe × de The amount of work actually done by the machine against the resistance is called the work output Work output equals the resistance force multiplied by the distance the resistance moved work output = fr × dr
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Simple Machines and Work Work output can never be greater than work input because energy cannot be created The efficiency of a machine measures how much useful work it can do compared with how much work was put into it efficiency = work output/work input × 100% Efficiency is written as a percent, and multiplying by 100 tells you what percent of the work input is converted to work output ALL machines have efficiencies that are less than 100 percent
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Mechanical Advantage A simple machine makes a task easier because it multiplies the force a person applies The number of times a machine multiples your effort force is called the mechanical advantage mechanical advantage = resistance force /effort force
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Mechanical Advantage Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage? MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3
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Mechanical Advantage Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage? MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3
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Mechanical Advantage Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage? MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3
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Mechanical Advantage Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage? MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3
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Mechanical Advantage You can increase the mechanical advantage of a lever simply by moving the fulcrum closer to the resistance and farther from the effort force The effort arm is the distance between the fulcrum and the effort force of a lever The resistance arm is the distance between the fulcrum and the resistance force of a lever MA = effort arm/resistance arm
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Mechanical Advantage To increase Mechanical Advantage in a pulley, simply add more pulleys For each pulley the MA is 1
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