THE PHYSICS OF DRIVING

The Force Is With You

Although I wish my version was in regard to a metaphysical and ubiquitous power in a galaxy far, far away, it’s actually in reference to you, as a driver, and the various laws of physics that apply to any moving object (your car in motion; objects in motion around your car) or stationary object (objects in motion around your car; your car’s stationary state). At any given moment, there are many natural forces acting on your automobile, regardless of whether or not you are moving. The following forces include:

  • gravity
  • inertia
  • momentum
  • kinetic and potential energy
  • friction

These forces have a direct impact on how your automobile performs, regardless of the design of your vehicle or how skilled you are at handling it.

Understanding the effects of each force

Understanding the basis of these forces will help you gain better control of your vehicle during your everyday commute. These basic laws are centered on turns, stops, and roadway driving conditions. Understanding how they affect your vehicle may also help you improve your reaction and response time during an emergency situation.

The laws of physics are prevalent at all times, in all things, and in all places. By misjudging and mishandling these forces you run the risk of losing traction control and misjudging stop time, which can ultimately lead to a collision.

In this article, we are going to go over the laws of physics in relation to driving and operating a motor vehicle. It is crucial you read this guide in its entirety if you truly wish to perfect your driving techniques–because as my good pal Murphy once stated, “if anything can go wrong, it will.”

Gravity

Any particle of matter in the universe attracts any other with a force varying directly as the product of the masses and inversely as the square of the distance between them.

Gravity, or gravitation, is a natural phenomenon where all things encompassing mass and energy are brought towards each other. In essence, it’s what pulls our bodies to the ground and keeps up from floating into Outerspace.

Traction results in the friction between the road and your tires, which is created by the weight (thanks, gravity) of the car pushing its tires on the road. Traction is what allows us to move forward, backward, and side to side.

Moving uphill

When you are driving uphill, the force of gravity is working against you, which is why you need to press on the accelerator a bit harder.

Moving downhill

When you drive downhill, the force of gravity works for you, causing your vehicle to move faster. This is why you will typically press the brakes to avoid going too fast.

Parking on a hill

When you park on a hill, the force of gravity is working against your vehicle. Therefore, you should place your vehicle in “park,” engage the parking brake, and as a safeguard (in the event your brakes fail) you should rotate your tires away from traffic and, if possible, facing the curb or the side of the road.

Inertia

If it is at rest, it will stay at rest. If it is in motion, it will stay at the same velocity.

Inertia is the resistance of any moving object to any change in its velocity when no forces act upon them.

For example, when you are stopped at a red light on a flat surface, you will not move forward unless you engage the accelerator or are pushed forward by a vehicle hitting you from behind.

As you are accelerating, momentum keeps your vehicle moving, unless it is interrupted by something, such as braking, steep inclines, or a very heavy or permanently affixed object in the ground, such as a tree, building, boulder, or another vehicle.

Inertia is what keeps your body moving after a sudden impact or stop is made to the vehicle. It is what whiplash and other injuries in a car accident.

Potential and kinetic energy

Energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another

Potential energy: Before energy is expressed in any form (kinetic, thermal or otherwise), it exists as potential energy. For example, when your car is stopped on a hill, gravity creates potential energy for your car. The second your car begins to roll downhill, the potential energy then becomes kinetic energy. All objects encompass kinetic energy while they are in motion. When an object is stationary, that kinetic energy is stored as potential energy.

Kinetic energy: Kinetic energy is expressed by motion. In the parked car example above, the only thing keeping the vehicle’s potential energy from becoming kinetic energy is the car’s brakes. In the event your brakes fail, the car will begin to roll and collect kinetic energy. The amount of kinetic energy an object has affects how easily it can be stopped. As speed increases, so does kinetic energy. The car in our example would be harder to stop, the further it rolls down the hill.

Momentum

For every action there is an equal and opposite reaction.

The force of any moving object is referred to as momentum. The momentum of an object is related to its weight and speed. For example, a football traveling at 15 MPH has more momentum (force) than an empty soda can traveling at the same speed.

While driving a vehicle, you are acquiring more momentum as you gain speed. If you increase your speed from 25 MPH to 45 MPH, you are essentially doubling your car’s momentum. Therefore, a crash at 45 MPH would be much more devastating than a crash at 25 MPH.

Friction

When an object A exerts a force on object B, object B exerts an equal and opposite force on object A.

Friction is a force that is caused by the contact of one surface to another. It results in the level of resistance applied to an object on a moving surface. As an example, it’s easier to slide a hockey puck across ice than it is across the asphalt because asphalt contains more friction than ice.

In relation to driving, the amount of friction is dependant on:

  • how heavy your vehicle is (the heavier your vehicle, the more friction there will be)
  • whether your tires are under-or-over inflated
  • the tread of your tires (the less tread you have, the less friction there will be)
  • roadway surfaces (the smoother the surface, the less friction there will be)

Stopping distance

The rate of change of momentum of a body is directly proportional to the force applied

Because friction is dependant on the weight of your vehicle, a car transporting 5 people has more friction and momentum than it would if it were transporting 1 person because the car carrying 5 people would be much heavier.  Remember, the weight of a vehicle assists in stopping the vehicle by creating more friction between the tires and the road.

So, the heavier the vehicle, the longer it will take the vehicle to come to a complete stop.

The importance of wearing your seatbelt

A properly fastened seatbelt will assist in diffusing the forces of inertia. If you are ever involved in an accident, the seatbelt restraints your body almost instantly. Seatbelt mechanisms have saved hundreds of thousands of lives since its advent. They prevent you from hitting the windshield and dashboard, which could result in serious injuries, including brain injury, broken bones, lacerations, and even death.

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