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Torque in Physics

Torque is a physical quantity in physics that describes the rotational effect of a force on an object. It is often referred to as the "rotational force" or "moment of force." Torque is essential for understanding the behavior of objects in rotational motion, such as the rotation of a wheel, the twisting of a screwdriver, or the operation of a wrench.

Definition of Torque

Definition of Torque (τ): Torque (τ) is the product of a force (F) applied to an object and the perpendicular distance (r) from the point of application of the force to the axis of rotation. Mathematically, it is expressed as:

τ = F * r * sinθ


  • τ (tau) is the torque.
  • F is the magnitude of the force.
  • r is the lever arm or the perpendicular distance from the axis of rotation to the line of action of the force.
  • θ (theta) is the angle between the force vector and the lever arm.

Key Points about Torque

  1. Direction of Torque: Torque is a vector quantity with both magnitude and direction. Its direction is determined by the right-hand rule: If you curl your fingers in the direction of the force, the thumb points in the direction of the torque.

  2. Unit of Torque: The SI unit of torque is the newton-meter (N·m). In the Imperial system, it is often expressed in foot-pounds (ft·lb).

  3. Lever Arm: The lever arm (perpendicular distance) plays a crucial role in determining the torque's magnitude. The longer the lever arm, the greater the torque for the same force.

  4. Angle θ: The angle between the force vector and the lever arm is important. Torque is maximized when the force is applied perpendicular (90 degrees) to the lever arm (sin θ = 1). If the force is applied at an angle, the component of the force perpendicular to the lever arm is used to calculate torque.

Example of Torque

Consider the following example of a wrench being used to tighten a bolt:

  • Force (F): When you apply a force to the handle of the wrench, you are essentially pushing or pulling on the handle.
  • Lever Arm (r): The lever arm is the distance from the center of the bolt (the axis of rotation) to the point where you are applying the force. It represents the distance from the axis to your hand.
  • Angle (θ): In this case, the force you apply is likely to be perpendicular to the lever arm, so θ is 90 degrees, and sin θ = 1.

To maximize the torque, you would:

  • Apply a larger force on the wrench.
  • Use a longer wrench handle (increasing the lever arm).
  • Apply the force perpendicular to the lever arm.

This would result in a greater torque, making it easier to tighten or loosen the bolt.

In summary, torque is essential for understanding rotational motion and is influenced by both the force applied and the lever arm's length and orientation. It plays a crucial role in many everyday applications, from turning a doorknob to the operation of machinery.

Published on: Sep 18, 2023, 03:16 AM  


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