Pumping the brakes.
In: Engineering
The coefficient of rolling friction is higher than the coefficient of sliding friction. What this means is that you actually “stick” to the road better when the tire is still rolling than if you’re sliding across the road. This is especially important on ice, where the friction is lower and you need every little bit of grip you can get.
In other words, the fastest way to stop the car is to brake the hardest you can while still keeping the tire rolling. If the tire stops rolling and you switch to sliding, it will actually take longer to stop. And while slowing, it is much easier to steer while the tire is rolling than when it is sliding.
In older cars, pushing the brake all the way down would lock the brake, causing you to slide. The way to counteract this was to manually lift your foot off the brake and allow the tires to start rolling again, then apply the brake again, and keep doing the brake-release-brake cycle until the car stops. This is called “pumping the brakes.”
Since the mid 1990s, anti-lock brakes (ABS) have become standard. ABS uses a computer to pump the brakes several times per second, far faster than any human can do it. ABS also can pump the brake on each wheel individually and ensuring each is at its maximum rolling friction, while a human using the brake pedal pumps all of them at once. For this reason, ABS is *far* more effective at slowing your car and keeping you in control than pumping is. If your car has ABS (which is likely unless your car is 30 years old,) you should not be pumping the brake.
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