A gravity knife is a folding knife which can be opened solely by the force of gravity or centripetal force. Also implied is usually some kind of locking mechanism to keep the blade locked in place once opened. A release lever releases the blade whilst folding back. Many such knives are spring loaded for easy release (opening) of the blade.

Types of gravity knives

Rampuri

The rampuri is the dreaded Indian gravity knife having a single edged blade usually about 9 to 12 inches long . It formed the basic weapon for indian thugs or "goondas" during the beginning of the 19th century. The rampuri is used even to this day by the local Indian mafia although sophisticated automatic pistols have largely taken their place