Driving like an old lady; no one wants to do it, and there isn’t a single person the road in America that likes being stuck behind someone who does. But have you ever stopped to think that maybe people who don’t zoom from stoplight to stoplight know something you don’t about their cars? It may well be that they’re getting 10 miles per gallon better driving the way they do than you are. Here’s why.

Cars use what are broadly defined as “friction brakes” to reduce speed. When you hit to Stop Pedal, carbon-metallic pads clamp down on the rotating disks (or drums) attached to your wheels and grab them. However, unlike a gear drive, these pads are designed to slip linearly over the surface to provide an infinite degree of reductive force. An unfortunate by-product of this slippage is heat. If you want to see this for yourself, rub your hands together very lightly but quickly for ten seconds. Notice the slight heat produced by the friction of their contact. Now, push your hand together very hard, hard enough to make it difficult to slide one against the other, and move them back and forth at the same pace. Unless your palms are made of asbestos, more than likely you won’t make it ten seconds before the pain overwhelms your willingness to proceed. Twenty seconds of this treatment is enough to blister even the most calloused palm.

Here’s where the physics come in. The First Law of Thermodynamics states that energy can never be created or destroyed; it can only change form. The heat produced by your car’s braking system, and the heat which just gave you second degree burns on your hands, had to come from somewhere. It had to be converted from some source in order to exist, but what is that source? In short: fuel. The heat produced by friction is converted from the kinetic energy (movement) of the rotating wheel. The wheel’s kinetic energy was transferred to it by the engine, which creates movement by converting chemical energy (fuel) through the process of combustion.

So what does all this amount to? What it means in practical terms is if you accelerate to a higher speed than you need to and then have to hit the brakes, you’re wasting fuel. So, peeling out from a stoplight, accelerating to 60 mph and then slamming on the brakes 500 feet away will create more heat, and thus use more fuel, than doing the same thing at 45 mph. That 15 mph difference is a gaping hole where your money goes, never to be seen again. And what have you accomplished really? You didn’t get where you were going any faster, because you had to stop for the car ahead anyway, but you sure wasted a whole bunch of dinosaur juice to do it.

So, the next time someone passes you at 20 over the limit and slams on his brakes, point your finger and laugh. All the way to the bank.