# Block and tackle - efficiency approximation - without friction factor

## Description

f is the number of sheaves in the purchase, and there is a roughly % loss of efficiency at each sheave due to friction, then:

Related formulas## Variables

eff | mechanical efficiency of the system (equal to one for an ideal frictionless system; a fraction less than one for real-world systems with energy losses due to friction and other causes) (dimensionless) |

S | number of sheaves in the purchase (dimensionless) |

χ | loss of efficiency at each sheave due to friction (dimensionless) |