Saturday, June 3, 2006

Much of the recent wave of increasing gas prices can be attributed to the law of supply and demand. If we can reduce demand, we can reduce the price.

The first way to reduce demand is to reduce the massive waste of our precious natural resources. Though governments need to be more proactive in creating legislation to encourage energy conservation and development of alternative and renewable energy resources, and automakers need to develop better fuel-efficient technologies, there are many steps we ordinary citizens can take to reduce consumption.

As a physicist, I see ubiquitous examples of incessant squandering of energy. Twenty-seven percent of our nation’s energy (70 percent of our fuel) is consumed by vehicles. I attempt to explain from a physicist’s point of view some simple steps that will drastically reduce demand of fuel and will help reduce the ever-increasing costs that affect us all.

From one of the first laws of physics, a body in motion (or at rest) stays in motion (or at rest) unless acted upon by a force. In applying a force to a body over distance, work is performed which increases the energy of motion (kinetic energy) of the body. In the case of automobiles and trucks, chemical potential energy from the fuel is converted into heat via combustion and a small percentage (usually around 20 percent) of this is converted into useful work to accelerate the vehicle.

By accelerating the vehicle, we increase its velocity and thereby change its kinetic energy (which is proportional to the square of velocity). For a large vehicle just under 8,000 pounds (Ford Excursion), I calculated that with today’s U.S. gas prices ($3 per gallon), it costs 10 cents to accelerate this behemoth from rest to 50 miles per hour (mph).

In this calculation, I neglected the massive loss of efficiency when an engine must accelerate from rest (especially the way many drivers accelerate “hard” putting the “pedal to the metal”) and thus, the real cost could be much higher. Think how many times we must stop and start when driving in city traffic to be more aware just how fast money is literally “burned” away by poor driving habits.

Whenever vehicles must accelerate, energy must be supplied (from the gasoline). When vehicles decelerate, this kinetic energy is lost and must be resupplied when resuming motion. Any situation where a vehicle can coast (for example to arrive in motion at a traffic light as it just turns green) will save much more energy (gas) than one might think. Thus, drivers should drive strategically. Look at the traffic lights far ahead and adjust driving speeds accordingly. When you see a red light, coast until you see it change. When you must stop, coast to diminish your speed as much as possible before braking. Cities should better design traffic lights to maintain flow and momentum of the maximum number of vehicles that travel at a designed speed.

Keeping more distance between cars also allows more time to coast and slow naturally than does hard braking. Often, with stop-and-go traffic, the increased time it takes to coast a fair distance between the car in front of you is enough so the front car starts moving and you don’t have to brake but instead move uninterruptedly.

Unnecessary braking not only causes accidents but wastes everyone’s energy. Rapid acceleration not only risks loss of control and overheating the vehicle but reduces engine efficiency during acceleration and wastes gas.

Removing unnecessary weight reduces the mass of your vehicle (and therefore the energy required to accelerate it). The kinetic energy is proportional to the mass. Idling of vehicles should be avoided as superfluous heat and greenhouse gases are generated for nothing.

Once a vehicle is in motion, the “natural” slowing in coasting relates to friction. Energy dissipated via friction ends up mostly as heat. Friction is seen in many forms from resistance to rolling of tires on the road to wind resistance/turbulence and resistance in moving parts of the engine. Maintaining the proper air pressure in tires is thus vital as underinflated tires have more surface contact with the road and therefore more friction.

Ensuring the brakes function properly also reduces friction. Removing unnecessary drag by leaving windows closed, removing superfluous or unused appendages and designing cars with reduced drag will reduce the energy lost as the vehicle moves in the wind.

The drag on vehicles is proportional to the square of the speed. Thus, a truck traveling at 77 mph experiences twice the frictional drag force as when it travels at 55 mph, neglecting any windspeed. Changing oil at scheduled intervals will reduce the cylinder/piston friction as replacement of old oil (with waste metallic particles sloughed-off from the cylinder walls) will reduce piston/cylinder friction. Use specified oils that are as low viscosity as possible to reduce friction. Bearings, axles and other moving parts should be well-lubricated.

Finally, maintaining the engine also reduces waste via more efficient combustion and cooling. Cleaning the carburetor and replacing the air filter, fuel filter and spark plugs can help dramatically improve fuel efficiency. Flushing the cooling system and using proper cooling fluid can go a long way to ensuring the engine operates properly by maintaining proper operating temperatures. A combustion engine’s efficiency directly relates to the difference between the high-temperature (after combustion) and the low-temperature reservoir.

My car is equipped with a digital gauge that measures instantaneous and average fuel efficiency. I was shocked when I watched how the fuel efficiency changed with different driving habits and conditions. Every car should be equipped with such a gauge so drivers can see how important their actions can be in saving or wasting fuel.


Assistant professor of physics

University of Nevada, Las Vegas (UNLV).

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