Pumping the brakes.
In: Engineering
In older cars, pushing the brake pedal hard will lock up the wheels completely so they no longer spin.
This is bad because the car will skid. When the wheels are locked, the car can’t turn at all to avoid a crash or stay on the road.
Pumping the brakes with your foot slows the car down while giving you a chance to turn the car since the wheels don’t lock up.
Newer cars have ABS (Anti-lock Braking System) brakes which just means the car pumps the brakes automatically, so you don’t have to.
Before all the cars had anti-lock brakes, you would have to pump your brakes to stop. If you just slammed on the car brakes, your car’s brakes would lock and force you into a skid. Hence the phrase “pump your brakes” meaning stop what you’re doing or slow down what you are doing otherwise you are going to have an accident. See, “slow your role.”
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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