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.

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

The formula for force of friction (F_f) is the same whether kinetic or static friction applies: F_{f =} μF_N. To distinguish between kinetic and static friction, μ_k and μ_s are often used in place of μ.

The Joule (J) is the standard unit of energy and has the unit \({kg \times m^2} \over s^2\).

Static friction is friction between two or more solid objects that are not moving relative to each other. An example is the friction that prevents a box on a sloped surface from sliding farther down the surface.