Curtis Arnold, age 11, of Pocatello, Ida., for his question:
WHEN WERE TRACTORS FIRST USED?
Tractors were first used during the 1870s. These tractors, called "traction engines," were large, four wheeled machines driven by steam. They could pull as many as 40 plows, but they were too awkward to be practical.
Smaller machines with internal combustion engines soon replaced the large tractors. But the new machines had only kerosene engines mounted on four wheeled frames. Later, kerosene or gasoline engines were built into the tractors.
Early tractors could do almost all of the farmer's field work. But they were too low to pull a cultivator through crops such as corn and cotton. Then, in the 1920s, the all purpose tractor was developed.
Early manufacturing companies usually made only one tractor model or size. But modern companies make a complete line. Modern tractors have both speed and power. And they are easy to operate, too.
There are two types: the wheel tractor and the tracklayer or crawler.
Wheel tractors make up about 97 percent of the tractors in the United States today. Most farmers use an all purpose tractor because it does a variety of jobs, such as planting, cultivating and harvesting. It has high rear wheels and either one or two small front wheels placed close together. These enable the tractor to be driven between rows of crops.
The smallest wheel tractors weigh about 3,000 pounds. Medium sizes weigh about 5,000 pounds and the largest more than 6,500 pounds. The demand for larger tractors is increasing.
Crawler tractors are driven on two endless tracks. They are steered by stopping or slowing one of the tracks. Crawler tractors are used for heavy jobs, for land clearing and for work on soft or rugged land.
The smallest crawlers weigh about 3,800 pounds while the largest ones weigh 50,000 pounds or more.
The modern tractor has built in features that provide power for other farm machines. These features include the drawbar, pulley, hydraulic pump and power take off.
The drawbar is a device for fastening equipment to the tractor for pulling. Tractors can then pull such equipment as plows, wagons, harrows, combines and hay balers.
The pulley attaches by a belt to another pulley on threshers, blowers and saw rigs to provide power.
The hydraulic pump provides the power to lift and lower the cutter bar on the moving machine, and the combine. It also adjusts the angle of the discs on the harrow, changes the depth of the plow in the furrows and operates a fork or shovel on the front of the tractor.
The power take off (PTO) provides power for machines that are either mounted on or pulled by the tractor. The PTO drives the moving parts of mowing machines, hay balers, combines, potato diggers and spray pumps.