what is a gravity knife

A gravity knife is a type of knife that opens its blade through the force of gravity. Unlike a switchblade, which extends its spring-propelled blade, a gravity knife uses a button, trigger, or fulcrum lever to release the blade from both the open and the closed positions. The blade is contained in the handle and may use a side-folding or telescoping (out-the-front, or OTF) blade. While most military gravity knives utilize a locking blade design, other types may not mechanically lock open but rely instead upon friction to wedge the rear section of the blade against the interior of the handle. There are various types of buttons, triggers, and fulcrum levers used to release the blade from both the open and the closed positions. In some countries, such as the United Kingdom, Canada, and certain U.S. states, a gravity knife is prohibited under the law as a prohibited weapon, with attendant criminal penalties.