The lever is a long plank, beam, or bar that is used to move heavy loads. Archimedes, a Greek mathematician, discovered the law of the lever and stated that if he were given a long enough stick and a place to stand, he could move the world. The beam rests on a firm object called the fulcrum. The point of resistance is the place where the load to be moved is located. The point where the force is applied to move the load is the point of effort. The closer the fulcrum is to the load, the less effort it takes to move the load.
A wheel is a cylindrical object that rotates about the axis of the cylinder. The axle is a rígid rod that goes through the center of the wheel and lies along the cylinder axis. The wheel and axle are dealt with as a single unit when they are rigidly joined to each other and work together as a unit.
A pulley is a grooved wheel. A rope is fitted into the groove and turns the wheel when pulled. A fixed pulley is attached to a support, and when one end of the rope is fastened to a load the load moves up. Force is not increased, but its direction has been changed. The person can stay in one place and use the weight of his body to help lift the load instead of carrying it.
The inclined plane is a very simple machine. It is a sloping surface that makes it easier to pull, push, or roll heavy loads. Instead of lifting a piano onto a truck, the movers can put a sturdy plank from the ground to the truck and roll the piano up onto the truck. They will use less effort but this effort has to be exerted over the greater distance the load now travels. A stairway is an inclined plane with steps forming its slope. In some places, such as baseball parks, people move from one level to another by way of ramps, which are inclined planes.
The screw is an inclined plane wound at its edge on a cylinder or cone. Archimedes is given credit for inventing the screw. A screw develops very large forces for lifting heavy weights and producing great pressures. Consider how tightly the threads hold two pieces of wood together or how a set of jackscrews can lift a house off the ground, how a jack lifts a car, and how tightly a vise holds metal and wood for cutting or shaping. The practical applications of the screw in common household fixtures are numerous: faucets, screw-in bulbs, screw-on bottle tops, any connection of water pipes, etc.
The wedge is essentially an inclined plane. The longer a wedge is compared to its thickness, the easier it is to force it through things. People who split logs use a wedge which is struck with an axe and driven into the wood. The farther it goes, the farther apart the two sections of the log move. Wedges increase force and are the basis of all cutting and piercing tools such as knives, needles, chisels, axes, nails, tacks, and pins, all of which push apart paper, wood, or cloth as they are driven in by pounding or pushing.
