Work is the moving of an object against an opposing force The object is moved by a push, a pull, or a lift. For example, when lifting a weight, it moves upward against the pull of gravity. Work is done on the weight. Work is measured in terms of distance and force Suppose a 5-pound weight is lifted 5 feet The work done on the weight is 25 foot pounds or 5 feet mes 5 pounds Distance mes force equals work In the metric system, work is measured in maler kilograms (n-kg) or jules) For example, lifting a 5-kg weight (11 pounds) a distance of one meter 13.28 feet) qaims 5 m-kg of work 136.08 n th).
The joule is a unit of measure of energy (15-2). One joule is the energy required to lift one kilogram (2.2 lbs] a distance of 10 cen timeters [3.9 inches] One foot pound equals Energy is the ability to do work When work is done on an ubject, energy is stored in that object, Lifting a weight (Fig 15-1) stores energy in it. The weight can do work if it is dropped Work as done on a car when it is accelerating Energy is being stored in t Work can be done slowly or it can be done rapully The rate at which work is done is called jawer. A mahime that can do a large amount of work to a shon time is a high Defection and expen TW three vids of thelon Expin pon dicent and Define ouerc efficiency and and honpower Define horsepower and expe 21 reboop te volume ciency and que Define me officiency and mectum officxy powered machine.
“Power” is the rate, or speed, at which work is done. Power requires motion. Something mant be moving Power is usually meatus Aurower (plor as Lila (kW) (metile Eater sectivos describe engine power measurements Tour in a twisting or turning force. You apply longue to Ue top of a screw kip jar when you on it (Fig. 18-2 You apply torque to the steering wheel when you see.
FRICTION
Friction is resistance to motion between two objects contact with each other. Suppose you put a book on a table and then pushed the book (Fig. 15-4). You find that it takes force to move the book. If you put a second book on top of the first book, you find it takes more force to move the tw books. The greater the load, the greater the friction There are three classes of friction. They are dry, greasy and viscou
1. DRY FRICTION This is the resistance to motion between two dry objects. An example is a board being dragged across a floor. The automotive braking system Torque, a twisting force, mt be applied to loosen car around a curve. The engine applies torque to the car wheels so they rotate uses dry friction to produce the braking action. Torque and power are not the same Torque is turning force which may or may not result in moton Power is the rate at which work is done This means something must be in motion Torque is measured in pound-feet (lb-ft). (Work is measured in foot-pounds [ft-lb)). For example, a 20-pound push on a 1 1/2-foot crank produces 30-pound-feet of torque (Fig. 15-3). The torque pushes on the crank whether it tus or not. The metric measurement of torque is made in next-meters Inertia causes an object to resist any change of speed or direction of travel. A motionless object tends to remain motionless. A moving object tends to keep moving at the same speed and in the same direction, Wham the automobile is standing still, its inertia must be Fig. 15-3 Tongir is measured in pind-fees (-) is soo en Ned a calcated by lying the ph by the akshaft iffat or the dice of the pub in the categ tion
2. GREASY FRICTION This is the friction between two objects thinly coated with oil or grease. Greasy friction occurs in the engine when first starting. The oil may have drained away from the bearings, cylinder walls, piston rings, and pistons. The thin film that remains provides greasy friction. However, it is not enough to protect the engine from wear. This is why most engine wear occur during initial starting and warm-up. The lubricating system quickly supplies oil as soon as the engine starts.