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A tractor (from Latin trahere) is a device intended for drawing, towing or pulling something which cannot propel itself. Most commonly the word is used to describe a vehicle intended for such a task on some other vehicle or object.
The most common use of the term tractor is for the vehicles used on farms. The farm tractor is used for pulling agricultural machinery or trailers, ploughing, harrowing and similar tasks. The classic farm tractor is a simple open vehicle with two very large driving wheels on an axle below and slightly behind a single seat (this and hence the steering wheel are not on the left or right but in the center) and the engine in front of the driver with two steerable wheels below the engine compartment.
There are usually three pedals on the floor of a tractor, right below the steering wheel. The pedal on the left is the clutch, the operator presses on this pedal to disengage the transmission for either shifting gears or stopping the tractor. The two pedals on the right are the brakes. The left brake pedal stops the left front and rear tires, and the right break pedal does the same with the tires on the right side. This independent left and right wheel braking augments the steering of the tractor. This is usually done when it is necessary to to make a tight turn. The operator presses both pedals at the same time to stop the tractor.
The throttle, unlike those in automobiles is generally controlled from a hand operated lever. This helps provide a constant speed in field work. It also helps provide continuous power for stationary tractors that are operating an implement. Some modern tractors have an additional pedal on the floor that serves as an additional throttle control, giving the operator more control over the speed of the tractor.
Most farm tractors use a manual transmission. They have several gears which generally provide a range of speeds from less than a mile per hour up to about 25 miles per hour. Compared to other vehicles, the tractor is quite slow. Slower speeds are necessary for most operations that are performed with a tractor. These slower speeds help give the farmer a larger degree of control in certain situations - such as field work. Older tractors generally require that the operator press in the clutch to shift the gears, but many modern tractors can shift between gears without the need to depress the clutch.
Modern farm tractors can be quite large with eight driven wheels, four on the front axle and four on the back axle, and articulated steering. Variations of the classic style are used for smaller farm tasks, mowing grass, and landscaping. The size - especially with modern tractors - and the slower speeds are reasons motorists are urged to use caution when encountering a tractor on the roads.
Modern tractors have roll over protection systems (ROPS) to prevent an operator from being crushed in the event of a rollover. This is especially important in open air tractors. In open air tractors the ROPS is a steel beam that extends above the operator's seat. For tractors with operator cabs, the ROPS is part of the frame of the cab. Before ROPS were required, many farmers were crushed to death when their tractors rolled over on top of them. Row crop tractors, before ROPS were particularly dangerous because of their 'tricycle' design with the two front wheels spaced close together and pointed inward toward the ground. Many farmers were killed by rollovers while operating tractors along steep slopes.
Most tractors have a means to transfer the engine's power to another machine such as a baler or mower. Early tractors used belts wrapped around pulleys to power stationary equipment. Modern tractors use a power take-off ( PTO) to provide rotary power to machinery that may be stationary or pulled. Almost all modern tractors can also provide hydraulic and electrical power.
Farm implements can be attached to the rear of the tractor by either a drawbar or by a three-point hitch. The three-point hitch was invented by Harry Ferguson and has been a standard since the 1960s. Equipment attached to the three-point hitch can be raised or lowered hydraulically with a contol lever. The equipment attached to the three-point hitch is usually completely supported by the tractor.