Counter-torque

Counter-torque, also sometimes called reaction torque, is the equal and opposite rotational force generated in response to an applied torque. It arises from Newton's Third Law of Motion (for every action, there is an equal and opposite reaction) when a rotating object exerts a force on another object. The magnitude of the counter-torque is equivalent to the applied torque, and its direction opposes the initial rotation, often manifesting as a twisting or rotating force that must be resisted. Understanding counter-torque is vital in engineering for designing stable systems and controlling movement.

Counter-torque meaning with examples

• When tightening a bolt with a wrench, the counter-torque is felt in your hand, as the wrench attempts to rotate in the opposite direction of the applied force. Without a secure grip, this counter-torque can cause the wrench to slip. The stronger the bolt is tightened, the greater the counter-torque will be, requiring more force from the user to maintain the bolt's tightening.
• In a helicopter, the main rotor generates a large torque, causing the helicopter's body to want to spin in the opposite direction due to counter-torque. The tail rotor is specifically designed to counteract this counter-torque, providing a stabilizing force that keeps the helicopter oriented correctly during flight. This careful balance of torque is critical.
• Automobile engines produce a significant amount of torque, and the counter-torque affects other components. For example, during acceleration the engine and wheels will produce torque. That causes a counter-torque that can twist the engine block or the chassis if these are not rigidly reinforced. Mounts are designed to absorb the counter-torque.
• In robotics, counter-torque is a fundamental consideration when designing robotic arms. If the motors move parts of the arm, then the arm experiences a counter-torque. Sensors and control systems must actively manage the counter-torque produced by the motors and the weight of the arm segments to ensure the arm maintains its desired position and trajectory with minimal deviations.