Torque

The Turning Effect: Understanding Torque

Torque, also known as moment of force, is the rotational equivalent of linear force. While a linear force causes an object to accelerate in a straight line, a torque causes an object to acquire angular acceleration—that is, to rotate, twist, or turn. It is a measure of how much a force acting on an object causes that object to rotate around a pivot point or axis. The magnitude of torque depends on three key factors: the amount of force applied, the distance from the pivot point at which the force is applied (known as the lever arm), and the angle at which the force is applied relative to the lever arm.

To get the maximum turning effect, you apply the force as far from the pivot as possible and at a right angle (90 degrees) to the lever arm. This is why it's easier to open a heavy door by pushing on the edge farthest from the hinges, and why a long wrench makes it easier to tighten a stubborn bolt. This converter helps you translate between the different units used to measure this turning force, including the SI standard (Newton-meters), the common US automotive and engineering unit (pound-feet), and the older metric gravitational unit (kilogram-force meter). This tool is essential for mechanics, engineers, physicists, and anyone working with rotating machinery or fasteners.

Relevant Formulas in Science and Mathematics

• Definition of Torque (Physics): The basic formula for torque is τ = rFsin(θ), where τ (the Greek letter tau) is torque, 'r' is the length of the lever arm, 'F' is the magnitude of the force, and 'θ' is the angle between the force vector and the lever arm. When the force is applied perpendicularly (θ=90°), this simplifies to the more common τ = r × F.
• Rotational Second Law (Physics): Similar to Newton's F=ma for linear motion, the rotational equivalent is τ_net = Iα, where τ_net is the net torque, 'I' is the moment of inertia (rotational mass), and 'α' is the angular acceleration.
• Power and Torque (Physics): The power (P) of a rotating system is the product of its torque (τ) and its angular velocity (ω): P = τω. This is how engine horsepower is calculated from torque and RPM.
• Work Done by Torque (Physics): The work (W) done by a constant torque is W = τθ, where 'θ' is the angular displacement in radians.

A Deep Dive into Common Torque Units

• Newton-meter (N·m): The SI unit of torque. It represents the torque resulting from a force of one Newton applied perpendicularly to the end of a moment arm that is one meter long. It is the standard for scientific and international engineering applications.
• Pound-foot (lbf·ft): An Imperial/US unit of torque, very common in the automotive industry in the United States. It represents a force of one pound-force applied at a perpendicular distance of one foot from the axis of rotation. It is often used to specify engine performance ("My car has 300 lb-ft of torque") and bolt tightening specifications in repair manuals.
• Kilogram-force meter (kgf·m): A gravitational metric unit of torque. It represents the torque produced by a force of one kilogram-force (the weight of a 1kg mass) applied one meter from the pivot. It is an older unit but may still be encountered in some contexts or regions.