Resistance during vehicle moving condition

Resistance during vehicle moving condition:
The moving vehicle has to overcome the following resistances:
1.    Air or wind resistance,
2.    Gradient resistance, and
3.    Rolling resistance.
Air resistance
Is the aerodynamic drag experienced by the vehicle while moving and depends upon the frontal area of the vehicle speed and the speed of the vehicle.
Gradient resistance
Depends u[on the weight of the vehicle and the steepness or the grade of the road. It is independent of the speed of the vehicle.
Rolling resistance
Is the resistance to rolling occurring due to the deformation of road and tyre and the losses occurring due to the dissipation of energy in the tyre. The factors which affect rolling resistance are mainly the inflation pressure of the tyre design. The effect of speed is rather negligible.
How overcome these resistances?
To overcome this high torque is required at the driving wheels when a vehicle is starting from rest, climbing a hill or accelerating. Due to the variable nature of resistance because of load and gradient changes, it is imperative that the engine power should be available over a wide range of road speeds. For this purpose, a device called a transmission or gear set is provided to permit the engine crankshaft to revolve at a relatively high speed while the wheels turn at slower speeds. The gear set is enclosed in a metal box called a gear box. The gear box is fitted between the clutch and the rear axle and helps the road wheels to get the power of the engine in varying ratios. The driving force or tractive effort used must be equal to the total resistance of the forces opposing the motion of a vehicle and keeping it moving along a road at uniform speed.

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