“The Physics of Driving: part 1”

The world around us must adhere to certain natural laws like gravity and inertia. The cars we drive must also adhere to these laws, not with the risk of citations or jail time, but as a matter of fact and function. Understanding these physical phenomena can help drivers better control their vehicles. In this week's blog, we will look at some of the common physics associated with driving a motor vehicle.  

Gravity: Gravity is the universal force of attraction between all forces. The force exerted on an object is related to the gravitational constant, the mass of the two objects, and the distance between them. This force pulls objects to the center of the object. So in our case on the Earth, down toward lower ground. This phenomenon can be felt when we drive up or down hills. The force of gravity accelerates our vehicles at 9.8 m/s2in a perpendicular direction to the center of the Earth. That is why steeper slopes increase your speed of descent faster than slow gradual descents. Pedal control is important on slopes of all sizes. When going up a hill to maintain a constant speed you will need to increase the amount of engine power. When descending letting off the accelerator and potentially pressing the brake will be required to maintain the speed limit. Hills can also obscure sight lines so be cautious when cresting hills.

Friction: Friction is a force caused by the contact of one surface on another. 

Static Friction and Rolling Resistance- The shape of the wheel greatly reduces static friction and allows your car to roll which uses less energy than sliding per se. The inflation of your tires and the type of tires dictate the amount of rolling resistance you will have. Having over or under-inflated tires will increase your rolling friction which increases the force requiring the car to work harder and increasing the amount of fuel you will need. Snow tires have bigger threads to grip the road during harsh weather conditions and are a necessity in winter months, but they will increase your rolling friction during dryer months. 

Air Friction or Drag- Along with making your vehicle look cool, car manufacturers are constantly doing wind tunnel tests to determine the aerodynamics of vehicles. Having a more aerodynamic vehicle will increase the fuel efficiency of the car because less air will impact and slow the vehicle down. 

Kinetic Friction- The friction between moving surfaces is called kinetic friction. This is the main friction that is involved with slowing you down. When your brakes are applied, your brake pads are pushed into your brake rotor which causes friction and slows your vehicle down. The amount of friction is determined by the normal force and the coefficient of friction. When your brake pads are old or worn out, the coefficient of friction is lower resulting in less braking power. The normal force is the force acting in the perpendicular direction, or the amount of force provided by the brake pedal through the system. As you increase or decrease the amount of pressure you place on the brake pedal in turn you are increasing or decreasing the amount of force slowing you down. More pressure means more force and faster slowing.

In this first installment of “The Physics of Driving”, we looked at gravity and friction. Understanding the physics of the world and how they act on your vehicle gives drivers insight into how to stop, turn, and operate in everyday driving situations. In next week's blog, we will look at potential and kinetic energy, momentum and inertia, and centrifugal forces.