The Physics Behind the Working of a Car

Physics is prevalent in every single phenomenon you can think about in daily life. Drinking water – involves physical concepts like gravity and fluid dynamics. The same goes for cars as well. Think about basic actions like applying the brakes, pushing on the accelerator pedal, turning along a curve – all of these actions require physics for their completion. That being said, there is one phenomenon that we should take a close look at, and that is – roll moment.

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What is a moment?

Before jumping onto roll moment, you need to understand what moment itself means. The moment is a common term that is used to describe torque. Torque (in cars) is a measure of the rotational force of the engine when it is in twisting motion. According to derivations, torque equals the product of force, radius, and the sine of the angle between the force and the arm (lever).

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What is roll moment?

Roll moment is a moment (torque) that is the product of force and a distance that causes the vehicle to roll.

The roll moment of the car is a product of these three quantities: -

• The sprung mass of the car (or the mass of the car that is supported by the suspension system)
• The acceleration of the car (this is generally the centripetal acceleration from when the vehicle is turning)
• The distance (lateral) between the center of mass of the vehicle and the roll axis of the car

Roll center

One of the important concepts that directly ties in with the roll moment is the roll center. The roll center is a theoretical point in the car. All the suspension forces act on the vehicle on this point. The roll center is decided based on the suspension geometry of the car.

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How to calculate the roll center?

The roll center can be calculated by making a diagram of the car's suspension system that includes the following parts:

• The location of the tire and the location of the wheel
• The MacPherson strut chassis mounting point of the car
• The MacPherson strut hub mounting point of the car
• Lower arm chassis or subframe mounting point of the car
• Lower arm hub mounting point

What factors are affected by roll moment adjustment

The following factors are affected by adjusting the roll moment of the suspension system:

• The on-throttle steering of the car
• The grip of the tires while turning around corners
• The traction rolling of the car (which negates the grip on the road)
• The tire wear and tear
• Ease of changing directions while changing the car
• The responsiveness of the car while making movements

By understanding the Physics behind the roll moment of a car, it is easier for drivers to better appreciate the workings of their cars.