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Simple Machines Physical Science Mrs. Black Spring 2010.

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Presentation on theme: "Simple Machines Physical Science Mrs. Black Spring 2010."— Presentation transcript:

1 Simple Machines Physical Science Mrs. Black Spring 2010

2 Work & Power Work is done when a force causes an object to move in the same direction that the force is applied. Work is done when a force causes an object to move in the same direction that the force is applied. Think of some work you have done today…. Think of some work you have done today…. In order for work to occur 2 things must occur: 1. A force must be applied to an object. 2. The object must move in the direction the force is applied. In order for work to occur 2 things must occur: 1. A force must be applied to an object. 2. The object must move in the direction the force is applied.

3 If you are holding a baby, why are you NOT doing work??

4 Force in 2 Directions When you exert a force in 2 directions- --for example when cutting grass you apply forces downward and forward (at an angle)—only part of your force does work—the part that is in the same direction as the motion of the object. (p 407) When you exert a force in 2 directions- --for example when cutting grass you apply forces downward and forward (at an angle)—only part of your force does work—the part that is in the same direction as the motion of the object. (p 407) (No movement—no work—no matter how much force is exerted!) (No movement—no work—no matter how much force is exerted!)

5 Calculating Work Work is done when a force makes an object move. More work is done when the force is increased or the object is moved a greater distance. Work is done when a force makes an object move. More work is done when the force is increased or the object is moved a greater distance. Work = force X distance Work = force X distance Force is measured in newtons (N) Force is measured in newtons (N) Work is measured in joules. Work is measured in joules.

6 Power Power is how quickly work is done. Something has more power or is more powerful if it can do more work in a certain amount of time. Power is how quickly work is done. Something has more power or is more powerful if it can do more work in a certain amount of time. Power = work done Power = work done time needed time needed Power is measured in watts. Power is measured in watts.

7 Machines A machine is a device that makes doing work easier. A machine is a device that makes doing work easier. Effort(force) put into work is called the input force. Effort(force) put into work is called the input force. The work you do on a machine is the input work. The work you do on a machine is the input work. The machine also does work by exerting a force to move an object over some distance. This force may be called the resistance force or output force. The machine also does work by exerting a force to move an object over some distance. This force may be called the resistance force or output force. Why would the force also be called a resistance force? Why would the force also be called a resistance force?

8 When you use a machine the output work can never be greater than the input work.

9 Changing Force p , fig 8 Work = Force X Distance Work = Force X Distance Work stays the same, but force can Work stays the same, but force can change. Machines can help make work change. Machines can help make work easier by allowing you to exert a smaller easier by allowing you to exert a smaller force over a longer distance. force over a longer distance. Ex.: ramp, Mechanical Advantage = output force Mechanical Advantage = output force input force input force

10 Changing Distance p 414 Some machines will allow you to exert a force over a shorter distance. In these machines the output force is less than the input force. The Mechanical Advantage in this type of situation would be less than one. Some machines will allow you to exert a force over a shorter distance. In these machines the output force is less than the input force. The Mechanical Advantage in this type of situation would be less than one. Ex. Lever (hockey stick, chop sticks) Ex. Lever (hockey stick, chop sticks)

11 Changing Direction p 414 Sometimes it’s easier to apply a force in a certain direction. Some machines allow you to change the direction of the input force—neither the force nor the distance is changed. The Mechanical Advantage in this situation is equal to one because the output force is equal to the input force. Sometimes it’s easier to apply a force in a certain direction. Some machines allow you to change the direction of the input force—neither the force nor the distance is changed. The Mechanical Advantage in this situation is equal to one because the output force is equal to the input force. Ex. Pulley Ex. Pulley

12 Efficiency The ability of a machine to convert the input work to output work is called efficiency. The ability of a machine to convert the input work to output work is called efficiency. Efficiency = output work X 100% Efficiency = output work X 100% input work input work AN IDEAL MACHINCE HAS 100% EFFICIENCY!!

13 Friction & Efficiency Reducing friction between objects will improve efficiency. Reducing friction between objects will improve efficiency. Can apply oil---discuss examples… Can apply oil---discuss examples…

14 Simple Machines A simple machine is a machine that does work with only one movement. A simple machine is a machine that does work with only one movement. Ex: inclined plane, lever, wheel & axle, screw, wedge, and pulley Ex: inclined plane, lever, wheel & axle, screw, wedge, and pulley A machine made up of a combination of simple machines is called a compound machine. A machine made up of a combination of simple machines is called a compound machine.

15 Inclined Plane A flat, sloped surface. A flat, sloped surface. Less force needed to move an object from one height to another. Less force needed to move an object from one height to another. As inclined plane becomes longer, the force needed to move the object becomes smaller.---mechanical advantage increases. As inclined plane becomes longer, the force needed to move the object becomes smaller.---mechanical advantage increases.

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17 Wedge An inclined plane that moves. An inclined plane that moves. Can have one or two sloping sides. Can have one or two sloping sides. Changes the direction of the force applied Changes the direction of the force applied Ex.: knife, axe, door stop, front teeth, Ex.: knife, axe, door stop, front teeth, Mechanical advantage increases as it becomes longer and thinner. Mechanical advantage increases as it becomes longer and thinner.

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19 Screw Another form of inclined plane. Another form of inclined plane. A screw is an inclined plane wrapped around a cylinder or post. A screw is an inclined plane wrapped around a cylinder or post. Also changes direction of force applied—the threads change the force to a force that pulls the screw into the material. Friction between threads and material hold screw in place. The more tightly wrapped the threads the easier it is to turn the screw. Also changes direction of force applied—the threads change the force to a force that pulls the screw into the material. Friction between threads and material hold screw in place. The more tightly wrapped the threads the easier it is to turn the screw.

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21 Lever Any rigid rod or plank that pivots or rotates about a point or fulcrum is a lever. Any rigid rod or plank that pivots or rotates about a point or fulcrum is a lever. How are levers classified? How are levers classified? First Class —changes the direction of the input force. Fulcrum closer to output force. Ex. Scissors, pliers, seesaws, crowbar. First Class —changes the direction of the input force. Fulcrum closer to output force. Ex. Scissors, pliers, seesaws, crowbar. Second Class —increases force, doesn’t change direction of input force. Fulcrum is on other side of output force. Ex. Doors, nutcracker, bottle opener, wheel barrow. Second Class —increases force, doesn’t change direction of input force. Fulcrum is on other side of output force. Ex. Doors, nutcracker, bottle opener, wheel barrow. Third Class —increase distance, do not change direction of input force. Fulcrum is on other side of input force. Ex.: fishing pole, baseball bat, shovel, wheel barrow. Third Class —increase distance, do not change direction of input force. Fulcrum is on other side of input force. Ex.: fishing pole, baseball bat, shovel, wheel barrow.

22 ____???__ class lever

23 Wheel and Axle A wheel and axle consist of two circular objects of different sizes that are attached in such a way that they rotate together. A wheel and axle consist of two circular objects of different sizes that are attached in such a way that they rotate together. Ex.: water faucet handle, 428 Ex.: water faucet handle, 428

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25 Pulley A pulley consists of a grooved wheel with a rope or chain wrapped around it. A pulley consists of a grooved wheel with a rope or chain wrapped around it. Fixed pulleys are attached to a structure above your head—when you pull down on the rope you pull something up. Ex.: sails on a boat Fixed pulleys are attached to a structure above your head—when you pull down on the rope you pull something up. Ex.: sails on a boat Movable pulley—attach object lifting—allows you to exert a smaller force to lift the object. Movable pulley—attach object lifting—allows you to exert a smaller force to lift the object.

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27 ?????????????????? ?????????????????? ??????????????????

28 Your Challenge!!! Create your own simple or compound machine according the instructions provided…. Create your own simple or compound machine according the instructions provided…. Don’t forget…MAKE IT FUN! Don’t forget…MAKE IT FUN!


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