A lawn mower (often spelled as one word - lawnmower) is a machine (electric or mechnical) used to cut grass to an even length. It was invented in Britain in 1830 by Edwin Beard Budding, primarily to cut the lawn on sports pitches and expansive gardens. Since many sports had just been invented in Britain that required a flat soft ground (such as croquet, tennis, football and rugby), a more efficient way of making grass a uniform length was needed, and so the lawn mower was born. Previously, grass was cut by hand using a scythe.
Electric lawn mower with rear catcher, side view
There are two main types of lawnmowers, those where a set of cylindrical blades spin in a vertical forwards motion, and those whose blades spin horizontally. The latter type are usually powered by engines running on petrol or other liquid fuels, although versions with electric motors are becoming increasingly popular. Cordless electric lawnmowers are also available for small lawns.
The simplest kind of mower is the manual push mower. These always use the cylindrical type blades. This works by spinning the cutting blade at a fast speed, with power supplied by the user pushing it, rotating its wheels, which are then geared to the cutting blades. The blade rotates forward over the grass, pulling it into the blade and against a fixed plate - the blade and plate cause a scissor-like slicing action which cuts the grass.
The simplest type of power mower is basically a push mower with an engine - the engine then both rotates the cutters and drives the machine forward. In the last twenty or thirty years, it is also common to find this type of mower with an electric motor as the power source, though this has the disadvantage of requiring a trailing power cord which limits its range, so these are only useful for relatively small lawns close to a power socket. There is also the obvious hazard with these machines of the possibility of mowing over the power cable.
Underneath rotary mower, showing mulching blade
An alternative mechanism for cutting grass is a horizontally spinning blade held close above the grass surface. This type is usually referred to as a rotary mower. One of the first companies to exploit this principle commercially was the Australian Victa company, in 1947. These mowers are always powered, either using an internal combustion engine or an electric motor. Usually, these mowers are moved by manual motive power - the onboard engine or motor only spins the blades. The most common type is fitted with wheels, but an alternative is the hover mower, in which the spinning blade also acts as a fan providing a lift force, lifting the mower bodily clear of the ground on the same principle as a hovercraft. Such mowers are very light and easy to manoeuvre, provided the grass surface is fairly even. Rotary mowers typically have an opening in the side of the housing where the cut grass is expelled. Some have a grass catcher attachment at that point to bag the grass clippings. Rear-catchers is another common design for the same purpose.
Special "mulching" blades are now also available for rotary mowers. The blade is designed to keep the clippings circulating underneath the mower until the clippings are chopped quite small. This avoids the need for bagging the clippings or raking the clippings. Not only does this save labour, as no organics are removed from the lawn, less fertilizer is needed.
On rotary mowers, the blade is seldom sharp enough to actually cut the grass blades. The speed of the blade simply tears the grass resulting in brown tips. By contrast the cylinder-type lawnmowers and manual lawnmowers usually work by scissor action on the blades and a cleaner cut is achieved.
Different grass lengths may be desirable at different times of the year or in different parts of the lawn. The height of the lawnmower can usually be adjusted to control the height of the cut grass. On older or less expensive lawnmowers, this is accomplished by manually moving each wheel to a different slot on the chassis. A more recent innovation is a "one-touch" height-adjust mechanism where the wheels are mounted on a frame separate from the rest of the lawnmower and the frame can be raised and lowered. In general, vertical mowers can cut closer to the ground than horizontal mowers.
Modern power mowers have a "deadman's switch" which requires the operator to hold a switch to keep the engine running. Typically this is an extra bar that is held against the handle. Should the operator drop "dead" or otherwise lose control of the lawnmower and release the bar, the engine is turned off. The switch may be mandated by local legislation.
All mowers which require a human to push or manoeuvre them become quite tiring once the area of grass to be cut becomes more than a few tens of square metres - in which case a popular alternative for larger domestic properties is the ride-on mower. These often resemble small tractors, with the cutting deck mounted amidships between the front and rear axles. Such machines allow the user to comfortably mow up to several hectares of grass in a reasonable amount of time. An alternative layout for a ride-on is a rear-mounted engine with rear-wheel steering, and a front-mounted deck. These mowers are generally more manoeuverable around tight corners than the tractor type, but are generally more expensive. Most of these machines cut using the horizontal rotating blade system, though usually with multiple blades.
Professional grass-cutting equipment (used by large establishments such as universities or local authorities, etc), usually take the form of much larger dedicated ride-on platforms, or attachments that can be mounted on a standard tractor unit. Either type may use rotating blades or the cylindrical blade type cutters.
Edge trimmers are specialized, hand-held mowers for cutting grass near fences, trees and other areas too small for a mechanized lawnmower. Hand powered grass clippers can used for the tightest spots.