NEWTON’S 3 LAWS OF MOTION IN RELATION TO CAR RACING

The first law: a car in straight-line motion at a constant speed will keep such motion until acted on by an external force. The only reason a car in neutral will not coast forever is that friction, an external force, gradually slows the car down. Friction comes from the tires on the ground and the air flowing over the car. The tendency of a car to keep moving the way it is moving is the inertia of the car, and this tendency is concentrated at the Centre of Gravity (CG) point.

This equation can be used to calculate weight transfer during acceleration by treating acceleration force as negative braking force. If you have acceleration figures in gees, just multiply them by the weight of the car to get acceleration forces (Newton's second law! – F = ma, where a = g, i.e. F = mg). Weight transfer during cornering can be analysed in a similar way, where the track of the car replaces the wheelbase and is always 50% (unless you account for the weight of the driver).

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Braking causes Lf to be greater than Lr. Literally, the “rear end gets light,” as one often hears racers say. Consider the front and rear braking forces, Bf and Br, in the diagram. They push backwards on the tires, which push on the wheels, which push on the suspension parts, which push on the rest of the car, slowing it down. But these forces are acting at ground level, not at the level of the CG. The braking forces are indirectly slowing down the car by pushing at ground level, while the inertia of the car is “trying” to keep it moving forward as a unit at the CG level.

The braking forces create a rotating tendency, or torque, about the CG. Imagine pulling a tablecloth out from under some glasses and candelabra. These objects would have a tendency to tip or rotate over, and the tendency is greater for taller objects and is greater the harder you pull on the cloth. The rotational tendency of a car under braking is due to identical physics.

By how much does Lf exceed Lr? The braking torque is proportional to the sum of the braking forces and to the height of the CG. Let's say that height is 20 inches. The counterbalancing torque resisting the braking torque is proportional to Lf and half the wheelbase (in a car with 50-50 weight distribution), minus Lr times half the wheelbase since Lr is helping the braking forces upend the car. Lf has a lot of work to do: it must resist the torques of both the braking forces and the lift on the rear tires.

Some topics in this essay:
HORSEPOWER Horsepower, Bh WLr, Gravity CG, AIR RESISTANCE, Albert Einstein, CG Let's, INTRODUCTION Physics, CG Imagine, Racing Club”, Bf Br, newton's law, braking forces, constant speed, move object, ground pushes, moving constant speed, moving constant, third law, car racing, kinetic energy, car moving, newton's third law, force move object, car moving constant, dissipate energy constant,