- Compound Pulley
Archimedes introduces the block and tackle.
The simple pulley enables the user to lift a load more easily by changing the direction from which the force is applied. When the rope is fixed at one end and another pulley is added, the system provides mechanical advantage by multiplying the applied force, making it possible to lift heavy loads. More pulleys can be added to the system, now known as a “compound pulley” system, further multiplying the effectiveness of the force applied.
As an indication of the benefit of the system, the addition of a second pulley to a one-pulley lifting mechanism halves the amount of force required to make the lift. A third pulley, properly rigged, reduces the amount of force required to a quarter.
In 250 B.C.E., the Greek scientist and inventor Archimedes (c. 287-212 B.C.E) adopted this principle by mounting several pulleys on the same axle to create a “block” that was much more convenient to use than a series of separate pulleys. A single rope-called the “tackle”-fixed at one end, can be threaded between a fixed block and around each of the pulleys (“sheaves”) in a movable block so that the load on the system is shared between the ropes under tension.
According to Plutarch, whose account provides us with the earliest record of the block and tackle, Archimedes used his new invention single-handedly to move a whole warship. Whether this is true we
cannot know, but the block and tackle has certainly been an essential tool for lifting and moving heavy loads ever since. It can be found today in the cranes and lifting gear used in construction, engineering,
freight loading, and warehousing as well as on almost every yacht and sailing boat, including small dingbats with the simplest of rigging.
SEE ALSO: BRAIDED ROPE, PULLEY, WINCH, LEVER, CRANE, ARCHIMEDES SCREW
- Controlled Fire
Fire is an essential tool, control of which helped to Start the human race on its path to civilization. The original source of fire was probably lightning, and for generation blazes ignited in this manner remained the only source of fire.
Initially Peking Man, who lived around 500,000 B.C.E, was believed to be the earliest user of fire, but evidence uncovered in Kenya in 1981, and in South Africa in 1988, suggests that the earliest controlled use of fire by hominids dates from about 1,420,000 years ago. Fires were kept alive permanently because of the difficulty of reigniting them, being allowed to burn by day and damped down at night. Flint struck against pyrites or friction methods were the most widespread methods of producing fire among primitive people.
The first human being to control fire used it to keep warm, cook their food, and ward off predators. It also enabled them to Survive in regions previously too cold for human habitation. They also used it in "fire drives" to force animals or enemies out of hiding. Controlled fire was important in clearing forest for roadways, grasslands for grazing, and agricultural lands-uncontrolled, the fire destroyed the potential of the soil. Mastering fire also opened up the possibilities of smelting metals, enabling humankind to escape the limitations of the Stone Age.
SEE ALSO: OIL LAMP, CANDLE, OVEN