Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement.  So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

Solving for R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{60 lbs. \times 7 ft.}{8 ft.} \) = \( \frac{420 ft⋅lb}{8 ft.} \) = 52.5 lbs.

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{160 lbs.}{40 lbs.} \) = 4

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.