Table of Contents
What Is Torque?
Torque, also known as the moment of force, is a measure of the rotational force applied to an object. It describes how much a force acting on an object causes that object to rotate around an axis. Torque is a vector quantity, meaning it has both magnitude and direction. The SI unit of torque is the Newton-meter (N-m).
In everyday life, torque is encountered when tightening a bolt with a wrench, opening a door, or pedaling a bicycle. The longer the wrench or lever arm, the more torque you can generate with the same force, which is the principle behind most mechanical advantage systems.
Torque Formula
Where τ is torque in Newton-meters, F is the applied force in Newtons, r is the lever arm distance in meters, and θ is the angle between the force vector and the lever arm. Maximum torque occurs when the force is perpendicular to the lever arm (θ = 90 degrees).
Common Torque Units
| Unit | Symbol | Conversion to N-m |
|---|---|---|
| Newton-meter | N-m | 1 |
| Pound-foot | lb-ft | 1.3558 |
| Kilogram-centimeter | kg-cm | 0.09807 |
| Dyne-centimeter | dyn-cm | 1e-7 |
Applications of Torque
- Automotive: Engine torque determines the pulling power of a vehicle. Higher torque at lower RPM means better towing capacity.
- Construction: Torque wrenches ensure bolts are tightened to specific values for safety-critical joints.
- Robotics: Servo motors are rated by their torque output, which determines the load a robotic arm can manipulate.
- Aerospace: Propeller torque is critical for aircraft engine design and performance calculations.
Frequently Asked Questions
What is the difference between torque and force?
Force causes linear acceleration of an object (F = ma), while torque causes rotational acceleration around an axis. Torque depends on both the magnitude of the force and the distance from the axis of rotation.
How does torque relate to power?
Power is the rate at which work is done. For rotational systems: Power (watts) = Torque (N-m) x Angular velocity (rad/s). In automotive terms, horsepower = torque (lb-ft) x RPM / 5252.
Why does a longer wrench make tightening easier?
A longer wrench increases the lever arm distance (r) in the torque equation. Since torque = F x r, doubling the lever arm halves the force needed to achieve the same torque.