重力刀（Gravity Knife），用单手打开保险后，押住保险且将刀头朝下，此时刀刃便会受重力影响而从握柄中掉出，十分简单但耐用／实用的设计；

• 匕首
• 小刀

A gravity knife is a knife with a blade contained in its handle, and which opens its blade by the force of inertia or gravity. As the gravity knife requires gravity or spinning motion to propel the blade out of the handle, it differs fundamentally from the switchblade, which opens its spring-propelled blade automatically upon the push of a button, switch, or fulcrum lever. The main purpose of this opening method is that it allows opening and closing to be done one handed, in situations where the other hand is occupied. A major historical use has been in issue to parachutists to cut off their parachutes when tangled in a tree or in similar situations.