Zip line courses can consist of one or many cables that are suspended between trees or man-made structures. Participants (often referred to as “zippers”) are suspended from a pulley that moves across the cable, propelled by gravity. The cables are mounted descending from a higher to lower point. The amount of incline as well as the weight of the zipper determines the speed at which the participant travels from point to point. Zip line courses can be designed purely for speed (adrenaline rush), while others are designed to allow zippers to enjoy the natural surroundings such as forest, jungle or waterfalls (often referred to as canopy tours). Others employ elements of both.