Physics Stuff

As long as the tires stay on the car, the ground pushing on them slows the car down. .
             When you turn the steering wheel, you are trying to get the front tires to push a little sideways on the ground, which then pushes back, by Newton's third law. When the ground pushes back, it causes a little sideways acceleration. This sideways acceleration is a change in the sideways velocity. The acceleration is proportional to the sideways force, and inversely proportional to the mass of the car, by Newton's second law. The sideways acceleration thus causes the car to veer a little sideways, which is what the driver wants when he/she turns the wheel. If you keep the steering and throttle at constant positions, you will continue to go mostly forwards and a little sideways until you end up where you started. In other words, you will go in a circle. .
             BRAKING.
             The figure below shows a car and the forces on it during a "one g- braking manoeuvre. One g means that the total braking force equals the weight of the car, say, in kilograms. .
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             In this figure, the black and white "pie plate- in the centre is the "Centre of Gravity point- (CG). G is the force of gravity that pulls the car toward the centre of the Earth .
             (F = mg - Newton's second law of motion). This is the weight of the car; weight is just another word for the force of gravity. It is a fact of Nature, only fully explained by Albert Einstein, that gravitational forces act through the CG of an object, just like inertia. .
             Lf is the lift force exerted by the ground on the front tire, and Lr is the lift force on the rear tire. These lift forces are as real as the ones that keep an airplane in the air, and they keep the car from falling through the ground to the centre of the Earth. .
             We don't often notice the forces that the ground exerts on objects because they are so ordinary, but they are at the essence of car dynamics. The reason is that the magnitude of these forces determines the ability of a tire to stick, and imbalances between the front and rear lift forces account for understeer and oversteer.