Remember the old "Flintstones" cartoon where Fred Flintstone would push his feet down to the ground to stop his car? Our car brakes today are surprisingly similar: We put our feet down, and the car stops. In our case, though, there are a couple things between us and the road -#- tires, brakes and an amazingly useful and underappreciated liquid we call "brake fluid."

Without brake fluid, there's no way for the pressure you apply with your feet to make it to the brakes. It's like Fred reaching down with his feet, but not quite being able to reach the roadway -#- not a good feeling when you're heading down a winding hill.

Because liquids are by nature relatively uncompressible (that is, applying pressure to a liquid doesn't appreciably decrease its volume), it makes an ideal medium to transfer pressure from your foot to the brake without losing force. An advantage of brake fluid over a strictly nonliquid mechanical option is that the driver doesn't feel the strong forces at work on the brake pads, where temperatures can soar to around 800 degrees Fahrenheit (426.7 degrees Celsius).

If you look at a 19th century stagecoach, you'll see a big lever on one side -#- this is what they pulled to stop the carriage. Just imagine the vibrations shooting up your arm, especially if you needed to stop quickly. [Qingdao Gofar]