12.3 Simple Machines

Inclined Plane An inclined plane is a flat, sloped surface (ramp) An inclined plane allows you to exert your input force over a long distance The input force needed is less than the output force The input force used is the force with which you push/pull an object The output force is the force you would need to lift the object without an inclined plane To determine the mechanical advantage, you would divide the length of the incline by the height

Wedge Give an example of a wedge A wedge is a device that is thick at one end and tapers to a thin edge at the other end Instead of moving an object along the inclined plane, you move the inclined plane itself The mechanical advantage can be determined by dividing the length of the wedge by its width

Screws A screw can be thought of as an inclined plane wrapped around a cylinder; the spiral inclined plane forms the threads of the screw Twisting a screw into a piece of wood exerts an input force on the screw The threads of a screw act like an inclined plane to increase the distance over which you exert the input force Friction between the screw and the wood holds the screw in place The closer together the threads of a screw are, the greater the mechanical advantage The mechanical advantage can be found by dividing the length around the threads by the length of the screw

Levers Give an example of some levers A lever is a rigid bar that is free to pivot, or rotate, on a fixed point The fixed point that a lever pivots around is called the fulcrum 3 classes of levers: 1st class-always change the direction of the input force; if fulcrum is closer to the output force, the levers increase force; if fulcrum is closer to input force, these levers increase distance; scissors, pliers, seesaws 2nd class-levers increase force, but do not change the direction of the input force; doors, nutcrackers, bottle openers 3rd class-increase distance, but do not change the direction of the input force; fishing poles, shovels, baseball bats

1st Class Levers 2nd Class Levers 3rd Class Levers

Wheel and Axle A wheel and axle is a simple machine made of two circular or cylindrical objects fastened together that rotate about a common axis The object with the larger radius is the wheel and the smaller radius is the axle The wheel and axle increases your force, but you must exert your force over a long distance

Pulley A pulley is a simple machine made of a grooved wheel with a rope or cable wrapped around it You use a pulley by pulling on one end of the rope, which is the input force. The output force pulls up on the object you want to move To move a heavy object over a distance, a pulley can make work easier in 2 ways: it can decrease the amount of input force needed to lift the object; the pulley can change the direction of your input force 2 basic types of pulleys: A fixed pulley is one you attach to a structure (flagpoles) A movable pulley is one you attach the object you wish to move (crane) Put a fixed and movable pulley together and you get a block and tackle

Compound Machines A compound machine is a machine that utilizes 2 or more simple machines