The culture based around the idea of parkour is a sport entirely based around momentum. The idea is to be able to control your movements to be able to maintain your momentum while running around. Normally parkour involves a lot of vertical movement, as well as large horizontal movements. The difficulty comes from having the strength to pull yourself up and over obstacles, or if you're good enough being able to stay at speed and direct your momentum to allow for fluid movements in all directions. Classic examples of this are wallrunning to cross a gap, or using a corner to jump to a higher height. By using the wall, they run up and jump off, using their forward momentum to help keep traction, allowing them to gain extra upward momentum. While there are many different ways one can "Parkour", it's often done in an urban setting, which means there is a lot of hard ground if they fall. One technique that is used to avoid hurting one's self when jumping from a height is rolling when landing. The idea is to land loosely on your feet, bending your knees and tucking into a forward roll. This slows down the impact, and obviously greatly reduces the chance of injury. Once you have the physical aspect down, many people like to add flair to their routines, doing tricks and flips to add style to their maneuvers. Lots of these things involve doing these tricks while transferring from one stunt to the next. This is why it has become a sort of art to people, having their own style and look to make their own kind of parkour.