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If one drive wheel turns more rapidly than the other, the machine moves along a curved path. If both wheels turn at the same speed, the machine follows a straight path. If one wheel stops and the other turns, or if the wheels turn in opposite directions, the mower pivots. [7] [9] [10] This drive system can be used on two types of zero-turn mowers:
Pei is best known for his work in cartography. Although map making and use of the grid existed in China before him, [41]: 106–107 he was the first to mention a plotted geometrical grid and graduated scale displayed on the surface of maps to gain greater accuracy in the estimated distance between different locations.
A simple machine uses a single applied force to do work against a single load force. Ignoring friction losses, the work done on the load is equal to the work done by the applied force. The machine can increase the amount of the output force, at the cost of a proportional decrease in the distance moved by the load.
The early unit was a grain of wheat or barleycorn used to weigh the precious metals silver and gold. Larger units preserved in stone standards were developed that were used as both units of mass and of monetary currency. The pound was derived from the mina (unit) used by ancient civilizations.
(Considered an early type of "coherer"). 1885: Edison takes out a patent [16] [non-primary source needed] on a system of wireless communication between ships via electrostatic induction through sea water. The system proves to be too short range to be practical. [17] 1887 experimental setup of Hertz's apparatus.
In early days the flexible two-wheeled dray, with a centre pole and narrow 3-inch (8 cm) iron tyres was commonly used. The four-wheeled dray or box wagon came into use after about 1860 for loads of 6 to 8 long tons (6.7 to 9.0 short tons; 6.1 to 8.1 t) and was drawn by 16 to 18 bullocks.
An early determination was that between Potsdam and The Brocken in Germany, a distance of about 100 miles (160 km), in 1906. [114] In 1911 the French determined the difference of longitude between Paris and Bizerte in Tunisia, a distance of 920 miles (1,480 km), and in 1913–14 a transatlantic determination was made between Paris and Washington .
[10] [12] In the 12th century, William of Malmesbury wrote that Eilmer of Malmesbury, an 11th-century Benedictine monk, attached wings to his hands and feet and flew a short distance, [10] but broke both legs while landing, also having neglected to make himself a tail. [12] Many others made well-documented jumps in the following centuries.