When a vehicle starts to move a lot of resistance comes to stop the vehicle. In this article, I will discuss the different types of resistance in vehicles.
Different Types of Resistance on Vehicles
At various engine speeds and gear settings, the tractive effort—or thrust—the engine delivers at the driving wheels changes. A lot of forces together referred to as resistance started to stop moving objects. The total effort necessary to keep the vehicle moving is equal to the sum of all opposing forces. If the tractive effort is excessive compared to the total of all the resistances, the vehicle will accelerate, but if it is insufficient compared to the total of all the resistances, the vehicle will decelerate. The following are the principal forces that work against the vehicle’s motion –
- Rolling resistance.
- Wind or air resistance.
- Gradient resistance.
These are three types of resistance that pull back the vehicle. Each of these resistances is discussed below.
1. Rolling Resistance
The rolling resistance is the force experienced by a vehicle’s tires when they roll over a surface. It occurs due to the deformation of the tire and the energy dissipated as heat during the contact patch. There are many factors that affect the rolling resistance-
(I) Tire Type and Design
The type and design of tires play a significant role in determining rolling resistance. Tires with lower rolling resistance, typically made from harder compounds and featuring advanced tread patterns, help reduce energy losses.
(II) Tire Pressure
Maintaining proper tire pressure is essential to minimize rolling resistance. Underinflated tires increase resistance as more of the tire surface contacts the road.
(III) Road Surface Conditions
The quality and texture of the road surface can affect rolling resistance. Rough surfaces or uneven pavements tend to generate higher resistance, decreasing the overall efficiency of the vehicle.
Rolling resistance, RR = KR. W= KR m g
where KR = Constant of rolling resistance,
W = Weight of the vehicle in Newton,
m = Mass of the vehicle in kg, and
g = Acceleration due to gravity = 9.81 m/s2
The value of KR generally varies from 0.0095 to 0.18 for best roads and loose sandy roads.
2. Wind or Air Resistance
The wind or air resistance depends upon the shape and size of the vehicle body and design. The air velocity and speed of the vehicle also matter in the wind resistance. When a vehicle moves, the atmospheric winds create pressure on the vehicle, and sometimes it tries to lift the vehicle. The aerodynamic design of the vehicle helps the vehicle to stay on the road and helps the vehicle to cut the air.
When calculating air resistance, air velocity is usually neglected. Mathematically,
Air resistance = RA (0.5 p. cd) AV2
where, p = Air density in kg/ m3
cd = Coefficient of drag,
A = Projected frontal area in m2, and
V = Vehicle speed in mis.
Generally, for calculating air resistance, it is easy to take the value of vehicle speed (V) in km/ h. Thus, air resistance,
where, Coefficient of air resistance = 0.0386 p _ cd ,
Projected frontal area in m2, and Vehicle speed in km/ h.
It may be noted that since the air resistance increases with the square of speed, at twice the speed, the air resistance is 4 times. For best-streamlined cars, the coefficient of air resistance (KA) is 0.023, for average cars, it is 0.032 and for buses and trucks, it is 0.045.
3. Gradient Resistance
The gradient resistance is due to the steepness of the road gradient. It depends upon the vehicle weight and the road gradient. Consider a vehicle standing on the gradient as shown in Fig.
Let w = Weight of the vehicle in N, and
Road gradient (i.e. inclination or slope of the road).
The weight of the vehicle W is acting vertically downwards. It has two components, W sin El is parallel to the slope and W cos El is perpendicular to the slope. Thus, mathematically,
Gradient resistance, RG W sin El = m g sin El …( ·: w=mg)
where m = Mass of the vehicle in kg, and
g = Acceleration due to gravity in m I s2 = 9.81 m I s2.
Total Resistance
The total resistance to the motion of a vehicle is the algebraic sum of all the resistances i.e. rolling resistance, wind or air resistance, and gradient resistance. When a vehicle is moving along a level road, it encounters only rolling and air resistance.ln such a case,
Total resistance, R = RR +RA
When the vehicle is moving up the gradient, it has to encounter the gradient resistance in addition to other resistances. In such cases,
Total resistance, R = RR + RA+ RG
The rolling resistance and gradient resistance are independent of the speed of the vehicle. A curve of total resistance against the speed of the vehicle is shown in Fig. The bottom line shows the air resistance, the lower middle line shows the gradient resistance and the next line above it shows the rolling resistance. The total resistance is shown by the topmost line. The total resistance is also called tractive resistance. It may be noted that to keep a vehicle moving at a constant speed, the tractive effort (F) equal to the total resistance (R) has to be applied.
Conclusion
Automobile vehicles encounter various types of resistance, which affects the fuel economy and performance. Reducing these issues can solve the engine’s power and performance.
Read more – What are the 10 tips to maintain your car?
Frequently Asked Questions (FAQ’S)
How does resistance affect a vehicle’s fuel efficiency?
Resistance increases the energy needed to maintain or increase the vehicle’s speed, leading to higher fuel consumption and decreased fuel efficiency.
Can resistance be completely eliminated?
Resistance cannot be completely eliminated as it is an inherent aspect of moving through any medium. However, it can be minimized through various techniques and advancements.
Are electric vehicles less susceptible to resistance compared to traditional vehicles?
Electric vehicles generally experience lower resistance due to their streamlined designs, regenerative braking capabilities, and lighter weights. These factors contribute to their overall efficiency advantage over traditional vehicles.
What role does resistance play in vehicle safety?
Resistance can impact vehicle safety by affecting handling and braking capabilities. Managing resistance allows vehicles to maintain better control and stability, ultimately enhancing safety on the road.
Can resistance impact the speed and acceleration of a vehicle?
Resistance directly affects a vehicle’s speed and acceleration. Increased resistance requires more power to overcome, resulting in slower speeds and reduced acceleration capabilities.
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