Final answer:
The camshaft in a four-stroke engine rotates at half the rpm of the crankshaft because it completes one revolution per four-stroke cycle, while the crankshaft completes two. Flywheels help smooth out engine vibrations by adding rotational inertia.
Step-by-step explanation:
In a four-stroke internal combustion engine, the camshaft rotates at ½ the rpm of the crankshaft because it needs to allow for four distinct engine strokes: intake, compression, power (or combustion), and exhaust. Each camshaft revolution completes one cycle of these four strokes. However, the crankshaft must complete two revolutions to go through all four strokes, which means for every two revolutions of the crankshaft, the camshaft completes just one. This is due to the mechanical linkage of the crankshaft to the pistons, as each piston stroke corresponds to a half rotation of the crankshaft.
Furthermore, nearly all conventional piston engines have flywheels that help smooth out engine vibrations. These vibrations are a result of the thrust of individual piston firings. The flywheel adds rotational inertia to the crankshaft, helping to maintain a smooth and continuous rotational speed despite the intermittent nature of power delivery from the pistons.