Simple Machines 6-5.7 Explain how the design of simple machines (including levers, pulleys, and inclined planes) helps reduce the amount of force required to do work. 6-5.8 Illustrate ways that simple machines exist in common tools and complex machines.

There are six common simple machines. Simple machine – device that helps reduce the amount of force required to do work. Make work easier by: allowing user to apply less force. allowing user to apply a smaller force over a longer distance. allowing user to change the direction of force applied There are six common simple machines.

Lever – rigid bar or board that is free to move around a fixed point called a fulcrum. Fulcrum may be placed at different locations along the bar.

Reduces amount of force required to lift a weight in two ways: increasing distance from fulcrum to point where effort force is applied, or decreasing distance weight is from fulcrum. By increasing distance effort force moves relative to distance weight moves, a lever can reduce effort force needed.

Fulcrum between, effort force and weight Ex: scissors, crowbar, seesaw, shovel.

Fulcrum on end, effort applied in middle, to lift weight on other end Ex: tweezers, broom, hammer.

Fulcrum on end, effort force applied on other end, to lift a weight in middle. Ex: wheelbarrow, bottle opener, nutcracker.

Pulley – a grooved wheel with rope running along groove. Changes amount and/or direction of force applied. By arranging pulleys in such a way as to increase distance that effort force moves relative to distance weight moves, a pulley can reduce effort force needed.

Movable pulleys reduce effort force. Ex: construction cranes part of block and tackle system Fixed pulley (attached to structure) can be found on top of flag pole and on window blinds. Single fixed pulley changes only direction of force (you pull down and weight goes up.)

Designed to reduce force needed to lift a weight in two ways: Inclined Plane – sloping surface that reduces amount of force required to lift object. Ex: Ramps, stairs Designed to reduce force needed to lift a weight in two ways: Increase length of ramp, or Decrease height of ramp.

By increasing distance effort force moves (ramp length) relative to distance weight is lifted (ramp height), an inclined plane can reduce effort force needed.

Inclined Planes that are… Wedges – one inclined plane or two back-to-back inclined planes Ex: knife blades, nails Screws – an inclined plane wrapped around a post or cylinder. Ex: screws, bolts, jar lids.

Wheel and Axles – consist of two circular objects: a central shaft (axel), inserted through middle of a wheel. Ex: door knobs, steering wheels, screwdrivers, gears, bicycle wheels

Complex (compound) Machines – consist of two or more simple machines. Ex: scissors (two levers & two inclined planes: wedges); fishing pole (lever, wheel and axle, pulley); bicycle (levers: handlebars & handbrakes; wheel and axles: gears, wheels, and pedals; screws)