by Nigel Holmes

Created on: July 18, 2009   Last Updated: March 27, 2012

The great scientist Sir Isaac Newton never saw an automobile, yet he can teach you how to improve your gas mileage. How can this be possible?

Newton concerned himself with motion. He studied the forces that put an object into motion, keep it moving, and bring it to a stop. These forces are all involved when we drive, so understanding his "Laws of Motion" can help us use gas more efficiently.

Getting a vehicle moving takes energy, and the amount of energy needed is proportional to the weight of the vehicle. So a lighter vehicle uses less gas to accelerate.

Weight can be reduced by taking out everything you don't need. Carry a toolbox in the trunk? Then take it out. The same goes for the child seats the grandkids use once a month, the old road atlas and the spare bottle of screen-wash. No point in using gas to accelerate these things up to 30 mph.

The rate of acceleration is also important. Gather speed slowly, and you'll use less energy than if you bury the gas pedal in the carpet.

You might be surprised to learn that braking is also a form of acceleration. When the brakes are applied, friction material is pressed against the brake rotors, converting motion into heat. Keep braking to a minimum, and you avoid wasting that energy.

Energy is also needed to keep the vehicle moving at a steady speed. This is because wind resistance and friction act against motion and will slow you down unless you continue to expend energy.

As your car rolls down the highway, it has to push air out of its way. When you're moving slowly, the air flows gently and little force is needed. At higher speeds it has to be moved faster, and this takes more energy. To make matters worse, wind resistance is proportional to the square of speed. In other words, it doesn't increase that much from say 30 to 35 mph, but from 70 to 75mph it increases a lot.

So what can you do to reduce wind resistance? First, drive slower. Drive on two lane roads rather than freeways because you'll be nearer to 55 mph than 70. Second, remove anything that interferes with the airflow. For example, take off roof-mounted storage boxes and roof racks.

A less obvious source of wind resistance is having the windows rolled down. At low speeds, this doesn't make much difference, but on the highway you definitely want to be using air conditioning.

There are two main sources of the friction that opposes forward motion: the tires and from within the engine. Tires have a 'stickiness' that has to be overcome to make them roll, and as they roll, the sidewalls deflect. This wastes energy as heat. Keeping the tires inflated reduces both the 'stickiness' and the sidewall deflection.

The engine in your vehicle has many moving parts that slide against each other. Minimize friction here by using a high-quality, low-viscosity engine oil, and remember to change it at the recommended intervals.

One last tip: Shut off the engine anytime you're not going to be moving for at least a minute. A good example is at a railroad crossing. After all, if you're not moving you're getting zero miles per gallon!

So in summary, Isaac Newton's "Laws of Motion" help us understand the forces that act on our motor vehicle. Driving gently will keep these forces low, leading to fuel-efficient driving. And efficient driving saves gas!

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