# 6 simple machines

## Wheel and Axel

A wheel and axle is a lever that rotates in a circle around a center point called the fulcrum.

A larger wheel rotates around a smaller wheel, called the axle.

The larger the outer wheel is in comparison to the inner axle, the more efficient the wheel and axle is.

## Pulley

If you have ever looked at the end of a crane, or if you have ever used an engine hoist or a come-along, or if you have ever looked at the rigging on a sailboat, then you have seen a block and tackle at work. A block and tackle is an arrangement of rope and pulleys that allows you to trade force for distance.

## Lever

Levers are one of the basic tools that were probably used in prehistoric times. Levers were first described about 260 BC by the ancient Greek mathematician Archimedes (287-212 BC).

## Screw

A screw is an inclined plane (a sloping or slanting surface) that is wrapped around a cylinder to form spiraling ridges. Screws look like spiral staircases. A common example of a screw is a wood screw. As this screw rotates, it moves into the wood a certain distance. This distance depends on the screw's pitch (the distance between the ridges winding around the screw). Each colored band on the paper around the pencil represents a spiral ridge on a screw, which is called a thread. Screws with less distance between the threads are easier to turn.

## Inclined Plane

A plane set at an angle to the horizontal, especially a simple machine used to raise or lower a load by rolling or sliding.

## Wedge

A wedge is a triangular shaped tool, a compound and portable inclined plane, and one of the six classical simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place.

## Converts

An interesting museum near St. Mark's Square in Venice displays two models of machines designed by Leonardo Da Vinci's that convert rotary motion into vertical motion. In one particularly ingenious machine, a cam that is three-quarters of a circle is in continuous contact with another circle (two reduction gears) until the circle breaks and the smaller gear turns wildly by gravity, and a hammer falls. Are there markets that turn around and around a fixed point in revolution, such as soybeans and oil (note soybeans below \$6 a few days ago, before oil topped \$70), that lead to the vertical motion of a third market?