# Torque to lower a load (by lead screw-related to the coefficient of friction))

## Description

A leadscrew (or lead screw), also known as a power screw or translation screw, is a screw used as a linkage in a machine, to translate turning motion into linear motion.

The torque required to **lower** a load can be calculated by “unwrapping” one revolution of a thread. The force of the load is directed downward, the normal force is perpendicular to the hypotenuse of the triangle, the frictional force is directed in the opposite direction of the direction of motion (perpendicular to the normal force or along the hypotenuse), and an imaginary “effort” force is acting horizontally in the direction opposite the direction of the frictional force. Using this free-body diagram the torque required to **lower** a load can be calculated

## Variables

T_{lower} | Torque (N*m) |

F | Load on the screw (N) |

d_{m} | Mean diameter of the screw (m) |

π | pi |

μ | Coefficient of friction depending on the material (dimensionless) |

α | one half the thread angle (deg) |

l | Lead (m) |

T_{c} | frictional torque of the thrust collar (N*m) |