12.3

1. 12.3 Simple Machines

2. 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

3. 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

4. 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

6. 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

7. 1st Class Levers 2nd Class Levers 3rd Class Levers

8. 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

9. 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

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