question: why does a car start when we push it ?
comment: A car starts when you turn the engine manually. Normally this is done by the starter motor, which turns the engine when you turn the key. But because the wheels are connected to the engine (assuming you're not in neutral and you don't have your foot on the clutch pedal), pushing the car turns the engine. So it starts. This is why, when you're working on your petrol-powered lawn mower, the manual always says that you should disconnect the spark plug first. Because otherwise, when you're turning the blade by hand in order to remove junk and grass, the engine could start. Ever seen those videos on Youtube when they start the engine of a plane by turning the propeller by hand? Same thing.
passages: The most common way to push start a vehicle is to put the manual transmission in second gear typically, switching the ignition to on/run, depressing the clutch, and pushing the vehicle until it is at a speed of or more, then quickly releasing the clutch to make the engine rotate and fire, then quickly depressing the clutch so it does not stall. This is done by one person pushing a lightweight automobile, pulling or being pushed by another vehicle or even rolling down a hill.
  
  Section::::Types.
   Push starting is most successful when the automobile is using a gasoline engine, uses a carburetor, and uses a capacitor discharge ignition (CDI) or an inductive discharge ignition system. Automobiles with other types of engine, ignition, and fuel delivery configurations may work, but may be more difficult to start. Some engines must have a battery providing some electricity since fuel injection systems must have power to operate.
  
  Section::::Types.:Automatic or manual gearbox.
   Push start
  
  Push starting, also known as bump starting, clutch starting, popping the clutch or crash starting, is a method of starting a motor vehicle with an internal combustion engine by engaging the manual transmission while the vehicle is in motion. The technique is most commonly employed when other starting methods (automobile self starter, kick start, jump start etc.) are unavailable.
   Kick start
  
  Kick start is a method of starting an internal combustion engine (usually that of a motorcycle) by pushing a ratcheting lever with one's foot. Kick start mechanisms were almost universally a part of motorcycle engines before the mid-1970s, and were phased out of production over the next twenty years or so as electric starters became standard equipment. There are still some motorcycles produced that have both kick and electric starters. 
   As diesel engines have become larger and their mechanisms heavier, air starters have come into use. This is due to the lack of torque in electric starters. Air starters work by pumping compressed air into the cylinders of an engine to start it turning.
  
  Two-wheeled vehicles may have their engines started in one of four ways:
  
  BULLET::::- By pedaling, as on a bicycle
  
  BULLET::::- By pushing the vehicle and then engaging the clutch, known as "run-and-bump starting"
  
  BULLET::::- By kicking downward on a single pedal, known as "kick starting"
  
  BULLET::::- By an electric starter, as in cars
   Section::::Non-motor.:Fuel-starting.
  
  Some modern gasoline engines with twelve or more cylinders always have at least one or more pistons at the beginning of its power stroke and are able to start by injecting fuel into that cylinder and igniting it. If the engine is stopped at correct position, the procedure can be applied to engines with fewer cylinders. It is one way of starting an engine of a car with stop-start system.
  
  Section::::See also.
  
  BULLET::::- Coffman starter
  
  BULLET::::- Flame-start system
  
  BULLET::::- Hucks starter
  
  BULLET::::- Hybrid Synergy Drive
  
  BULLET::::- Vincent Hugo Bendix
  
  Section::::External links.
  
  Section::::External links.:Patents.
  
  BULLET::::- , Clyde J. Coleman
   The exact origin of the phrase is unclear, and there have been several conflicting accounts of who was the first to recite it, and what the exact wording of it was. Prior to World War II, it was commonplace for an aerial bomb to signal the start of the engines. Seth Kline was the official starter of the "500" in 1925–1926 & 1934–1953. Kline is thought to have made an informal "Gentlemen, start your motors!" command as early as 1948 to accompany the bomb. The first documented case was in 1950, and that was recited by prolific public address announcer John Francis "Irish" Horan. Kline was again reported as saying it in 1951, (though some report it was Horan) Either Kline or Horan said it again in 1952. It was around that time the command was changed from ""...motors!"" to ""...engines!"" The participants and officials alike, preferred the more technical term "engines" to describe their machines. Sid Collins stated that chief steward Harlan Fengler explained to him "there are no motors in the race, just engines."
   The switching on of the ignition starts the engine and, in addition, automatically restarts the engine whenever it stalls, as long as the ignition is switched on.
   BULLET::::- Third: See that spark control lever, which is the short lever located on top of the steering wheel on the right side, is back as far as possible toward the driver and the long lever, on top of the steering column controlling the carburetor, is pushed forward about one inch from its retarded position.
  
  BULLET::::- Fourth: Turn ignition switch to point marked "B" or "M"
   Fuel injection is most common for modern gasoline and diesel engines. Fuel injection needs electrical power to open and close the fuel injectors. If a battery is of a sufficiently discharged state that it cannot provide the power to turn an automobile self starter then it may also not be possible to activate the injectors. The most common method to start such a vehicle engine is to jump start it.
   All internal combustion engines require some form of system to get them into operation. Most piston engines use a starter motor powered by the same battery as runs the rest of the electric systems. Large jet engines and gas turbines are started with a compressed air motor that is geared to one of the engine's driveshafts. Compressed air can be supplied from another engine, a unit on the ground or by the aircraft's APU. Small internal combustion engines are often started by pull cords. Motorcycles of all sizes were traditionally kick-started, though all but the smallest are now electric-start. Large stationary and marine engines may be started by the timed injection of compressed air into the cylinders — or occasionally with cartridges. Jump starting refers to assistance from another battery (typically when the fitted battery is discharged), while bump starting refers to an alternative method of starting by the application of some external force, e.g. rolling down a hill.
   A vehicle with a manual transmission may be push started. This requires caution while pushing the vehicle and may require the assistance of several persons or another vehicle. If the vehicle battery cannot provide power to the ignition system, push starting may be ineffective. Most vehicles with automatic transmissions cannot be started this way because the hydraulic torque converter in the transmission will not allow the engine to be driven by the wheels.
  
  Section::::Other methods.:Military vehicles.
   Renault introduced the technology in all of its European models in 2010.
  
  Section::::Carmakers and models.:Roewe.
  
  In 2009, Roewe's Rover 75 based 750 was fitted with stop-start as standard with the hybrid 1.8 Rover K-series engine.
  
  Section::::Carmakers and models.:SAAB.
  
  A Start/Stop function was fitted to the second-generation 9-5 in 2009. The button to control the system was placed next to the gearshift like SAAB ignition keys of old.
  
  Section::::Carmakers and models.:Suzuki.
   Section::::Hydraulic.
   A fuel pump is used for fuel injection. It can be mechanically driven or is electrically driven. If electrical then the same problem may arise which the battery cannot turn the pump because it is heavily discharged.
  
  A carburetor only needs suction from the internal combustion engine to work best when push starting. Once the engine is running, a fuel pump (mechanical or electrical) will continue to supply fuel to the carburettor.
  
  Section::::Types.:Ignition systems.
   Since automobile accessories like compressors and water pumps have typically been designed to run on a serpentine belt on the engine, those systems must be redesigned to function properly when the engine is turned off. Typically, an electric motor is used to power these devices instead.
  
  This technology has also been used on Honda Motor scooters in Asian markets for the last decade. Their PCX 125cc model was released in 2010 to be sold in Europe with this technology, though their North American model does not feature it.
  
  Section::::Characteristics.
   Section::::Starting.
  
  Internal combustion engines must have their cycles started. In reciprocating engines this is accomplished by turning the crankshaft (Wankel Rotor Shaft) which induces the cycles of intake, compression, combustion, and exhaust. The first engines were started with a turn of their flywheels, while the first vehicle (the Daimler Reitwagen) was started with a hand crank. All ICE engined automobiles were started with hand cranks until Charles Kettering developed the electric starter for automobiles. This method is now the most widely used, even among non-automobiles.
   Section::::History.
  
  Before the advent of the starter motor, engines were started by various methods including wind-up springs, gunpowder cylinders, and human-powered techniques such as a removable crank handle which engaged the front of the crankshaft, pulling on an airplane propeller, or pulling a cord that was wound around an open-face pulley.
   Section::::Diesel engines.:Starter motor.
   Starter (engine)
  
  A starter (also self-starter, cranking motor, or starter motor) is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric, pneumatic, or hydraulic. In the case of very large engines, the starter can even be another internal-combustion engine.
   Before the appearance of the starter motor, engines were started by various difficult and dangerous methods. These methods included: wind-up springs, gunpowder cylinders, and human-powered techniques such as a removable hand-crank. In 1896, the first electric starter was installed on an Arnold, one of the first motor cars manufactured in the United Kingdom. Charles Kettering and Henry Leland later invented and filed for the first electric starter in America in 1911. In 1912, the Cadillac Model Thirty became the first American car to have a starter installed.
   A vehicle equipped with an automatic transmission (including semi automatic) is difficult to push start since selection of transmission gears is possible only when the internals of such a gearbox are rotating. However, automatics with both front and rear hydraulic pumps can be push-started with no problems. The last American automobile with this type of transmission was the 1969 Chevrolet Corvair with a Powerglide automatic.
  
  Section::::Types.:Petrol or diesel engines.
   Section::::Electric.:Folo-Thru drive.
   In traffic, at a red light, many motorists will start to inch up in anticipation of the light turning green (watching the signal of the perpendicular traffic). This will give them a "head start" on other motorists on the road.
  
  Section::::In achieving a goal.
  
  A head start could be an improved start in an attempt to achieve some goal, such as in one's education or the completion of a task. In such cases, the head start is usually earned by working harder or by using more efficient means of reaching that point.
  
  Section::::See also.
  
  BULLET::::- Handicapping
  
  BULLET::::- False start
   Hand starting of aircraft piston engines by swinging the propeller is the oldest and simplest method, the absence of any onboard starting system giving an appreciable weight saving. Positioning of the propeller relative to the crankshaft is arranged such that the engine pistons pass through top dead centre during the swinging stroke.
  