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EQ: How do simple machines make work easier? Slide 2 Machines make doing work easier. But they do not decrease the work that you do. Instead, they change the way you do work. In general you trade more force for less distance or less force for more distance Slide 3 Changes the input force to greater output force (changes force) Allows you to exert your input force over a short distance (changes distance) Changes the direction of your exerted force (changes direction of the force) Slide 4 INPUT FORCEOUTPUT FORCE Force you exert on a machine Your push or pull The input force moves a machine a distance Using a shovel to lift dirt Input force: Your pull on the handle of the shovel Force the machine exerts on an object The machines push or pull The work the machine does by moving an object over a distance The shovel blade moving the dirt Slide 5 Where is the input force? Where is the output force? Slide 6 In some machines, the output force is greater than the input force. Less force, more distance Examples: Ramps Stairs Simple Machines: Inclined plane Slide 7 In some machines, the output force is less than the input force. More force, less distance Examples: Riding a bike in high gear Simple Machines: Wheel and axle Slide 8 Some machines change neither force nor distance. Output force equals input force Same force, same distance, direction changes Examples: Weight machine Knives Simple Machines: Pulley Wedges Screws Slide 9 A machines mechanical advantage is a number that tells how a machines output force compares to the input force. Mechanical advantage tells us how a machine changes force. Mechanical Advantage = Output force/Input force Slide 10 Increasing ForceIncreasing DistanceChanging Direction When the output force is greater than the input force. Can opener: Input force = 10 N Output force = 30 N 30N/10 N = 3 N MA = 3N You tripled your force! When distance is increased, the output force is less than the input force. Walking up a ramp Input force= 20 N Output force = 10 N 10N/20N = 0.5 N MA= 0.5 N Output force is less than input force, but its over a longer distance The input force will always equal the output force Slide 11 Machines make work easier. However, most machines are affected by the frictional forces In every machine, some work is wasted overcoming friction. The less friction there is the more efficient the machine will be. Slide 12 Many people think of machines as complicated devices such as elevators, cars or computers. Complex machines But some machines are as simple as a hammer, a shovel or a ramp. Simple Machines A simple machine does work with only one movement. Slide 13 There are six simple machines: Pulleys Levers Wedges Screws Wheel and Axles Inclined Planes Please Leave When She Walks In Slide 14 An inclined plane is a sloped surface Ramps, stairs, hills Less force is needed to move an object from one height to another using an inclined plane than is needed to lift the object. More distance is required As the IP becomes longer, less force is needed to move the object Slide 15 An inclined plane that moves is called a wedge. It can have two or more sloping sides They change the direction of the force being exerted to do work Examples: knives, axes, doorstops, teeth Slide 16 A screw is an inclined plane wrapped around a cylinder or post. Screws change the direction of the force being applied. Examples: screws, bottle tops, bolts, jar lids Slide 17 A lever is a plank that pivots or rotates about a point Changes force The point at which a lever pivots is called the fulcrum There are 3 classes of levers that are determined by the placement of the fulcrum, effort (input force) and resistance (output force) Changes force Slide 18 A first class lever looks like a see-saw with the fulcrum in the middle and the effort and resistance, (load) on either side. Examples: see-saw, scissors, pliers Slide 19 A second class lever has the fulcrum at one end, followed by the load and effort in that order. 2ELF Examples: wheelbarrow, Slide 20 A third class lever has its fulcrum at one end, followed by the effort and load. 3FEL Examples: baseball bat, golf club, fishing pole Slide 21 A wheel and axle is several levers joined together to form a circular pattern. Changes distance To be considered a wheel and axle, the wheel must turn the axle. If the wheel spins on an axle and does not turn it, it is simply a fulcrum in a lever. Examples : spigot for a hose, ferris wheel, doorknob Slide 22 A pulley is a grooved wheel with a rope or chain wrapped around it. Pulleys change the direction of the force needed to move an object. Pulleys can be fixed (flagpole, window blind) Or they can be moveable (construction crane) Slide 23 Slide 24 Dr. Machinellator, an evil dictator plans to take over the world. His nefarious goals include eliminating all but one simple machine from the Earth. As an expert in simple machines, you know that simple machines make work easier by changing the force, distance or direction of work being done. You even have a simple machine in mind that you consider the most important. Using your evidence from your machines notes and your debate, recommend which simple machine should survive The Machinellation. Be sure to explain and give evidence as to how this machine makes work easier (changing force, distance, direction), why the work it does is essential to human survival, and what would happen if your recommended machine was to disappear!