These cars are known as Lowriders, and they seem to be most popular in southern California. A Lowrider is any car that has modifications allowing it to ride very low to the ground. Some people really like the look.
The problem with a Lowrider is that things like speed bumps and rough roads can make driving difficult. To solve these problems, Lowrider enthusiasts install hydraulic lift kits that allow a completely adjustable height for the vehicle. These kits use electric hydraulic pumps and normal hydraulic cylinders like those described in How Hydraulic Machines Work to raise and lower the vehicle. Imagine connecting the cylinder along side the shock absorber or the spring and you get the idea. It's a pretty involved installation and can cost several thousand dollars.
What happened next was unpredictable and amazing -- it's one of those strange things that can happen in an evolutionary process. Someone at some point realized that, with enough power, the hydraulic system could make the car hop! Lowrider hydraulic systems quickly evolved to make hopping more and more interesting, until cars could eventually hop 6 feet off the ground! Originally there was one 12-volt or 24-volt pump driving all four wheels in unison. It is now possible to find cars that have four pumps (one for each wheel) and 8, 10 or even 12 batteries to power them. An 8 battery system typically contains two banks of four batteries, for a 48 volt x 2 system. 12 batteries create two 72 volt systems. These powerful systems are what you see in American movies.
Here are several interesting links: