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We have mentioned in passing a few times here on Planet Green that you will save gas if you strive to keep a relatively constant speed while driving. Our goal today is to elaborate a bit on that, and explain why that is the case. To some readers, it will seem very obvious. But we think that to many people who have never thought about it, it can be very useful to know. It's always easier to remember to do something when you understand how it works.

Lets start with Physics 101: Objects in movement tend to keep moving. But what's the difference between here on Earth and the vacuum of space? Friction. Your car has to fight friction from the tires on the road and from pushing against the air.

Once you are up to speed and cruising, your engine is basically working against that friction. Why is it less efficient to constantly slow down and accelerate instead of maintaining a relatively constant speed? Because every time you hit the brakes, forward-movement energy is converted to heat by the brake pads and lost. Every time you accelerate, your engine must fight against friction and inertia, and must work much harder than just to cruise at a constant speed.

It is the combination of these two things - energy lost as heat when braking, and extra energy necessary to increase speed - that makes changing speed unnecessarily a wasteful way to drive. Much better to keep a constant speed as much as possible. When you want to decelerate, it is better to coast down to that speed (just take your foot off the gas pedal, but don't hit the brakes).

We hope that now that you understand how it works, you will remember it the next time you are behind the wheel. It can save you money, and reduce the harmful emissions of your car.

Difficulty level: Easy.