Lever fulcrum to where the output force is applied (point "B"), then the lever amplifies the input force. On the other hand, if the distance "a" from the fulcrum to the input force is less than the distance "b" from the fulcrum to the output force, then the lever reduces the input force. The use of velocity in the static analysis of a lever is an application of the principle of virtual work. A lever is modeled as a rigid bar connected to a ground frame by a hinged joint called a fulcrum. The lever is operated by applying an input
Lever frame of them have been taken out of use. The lever frame is located in the signal box, which can be a building at ground level or a tower, separated from or connected to an existing station building. Early lever frames were also built as "ground frames" next to the track, without any form of shelter and were usually operated by traincrew and not permanently staffed. Especially in England, lever frames with the pivot underneath the floor of the signal box were common (as seen on the photo on the left). This design's relatively short lever angle is a major disadvantage,