تسجيل الدخول

تسجيل

The Lever

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-99

2025-11-05

534

is a rigid bar that is capable of movement about a fixed point called the fulcrum. There are three classes of levers, which are distinguished by the relative positions of the fulcrum and of the points of application of the applied force (power) and the resistance (weight).

FIG. 2.- First Class

• Levers of the First Class. -In a lever of the first class (AB, Fig. 69) the power is applied at one end P and the weight at the other, with the fulcrum between them.

The mechanical advantage in levers of this class may be either of speed or of force. If the power arm is greater than the resistance arm, the mechanical advantage is one of force; while if the power arm is less than the resistance arm, it is one of speed.

FIG. 2.-Second Class

• Levers of the Second Class. -In a lever of the second class (Fig. 2) the power is at one end and the fulcrum at the other, with the weight between them. In levers of this class the mechanical advantage is always one of force. It can never be one of speed, since the resistance arm is always less than the power arm.
• Levers of the Third Class. -The lever of the third class (Fig. 3) has  the weight at one end and the fulcrum at the other, with the power between them.

FIG. 3.-Third Class.

The mechanical advantage in this class of levers is always one of speed, since the resistance arm is greater than the power arm.