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Types of mechanical forces

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A force exerted on a body can cause a change in either the shape or the motion of the body.The unit of force in SI system is the Newton(N) and CGS system is dyne.No solid body is perfectly rigid and when force are applied to it,changes in dimension occur.such changes are not always perceptible to the human eye since they are negligible. For the example,The span of a bridge will sag under the weight of a vehicle and a spanner will bend slightly when tightening a nut. It is also important for civil engineers and designers to appreciate the effects of forces on materials.Together with their mechanical properties of the materials. There three main types of mechanical forces that can act on a body.They are 1)Tensile force 2) compressive force and 3) shear force
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Four stroke petrol engine

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Four-stroke cycle used in gasoline/petrol engines. 1 = Intake, 2 = Compression, 3 = Power, 4 = Exhaust. The right blue side is the intake port and the left brown side is the exhaust port. The cylinder wall is a thin sleeve surrounding the piston head which creates a space for the combustion of fuel and the genesis of mechanical energy.
A four-stroke engine (also known as four cycle) is an internal combustion (IC) engine in which the piston completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
  1. Intake: also known as induction or suction This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: also known as power or ignition This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: also known as outlet. During the exhaust stroke, the piston once again returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve

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