ABSTRACT
Levers, cranks, and connecting links are the basic elements of mechanical linkages. What is a lever? Figure 20.1a presents a bar hinged at one point and loaded by two forces F1 and F2 applied to its ends. Archimedes was apparently the rst who represented mathematically the principle of the lever: F1 ⋅ L1 = F2 ⋅ L2. That means, the sum of moments about the pivot point must equal zero: condition of static equilibrium. (By the way, the sum of forces must also equal zero; therefore the support reaction R equals F1 + F2.)
The lever transforms forces into torques. Any force exerted at any point of the lever (e.g., F1 in Figure 20.1b) can be resolved into two components:
• One of them (F1c) is directed along the line connecting this point with the pivot center (this component is neutralized by the pivot reaction and does not exert any turning moment on the lever).
