Torque and Couple

Torque is a turning force that causes an object to rotate around a fixed center point, known as the axis of rotation. A couple occurs when two equal forces act in opposite directions at different points on an object, making it rotate in place.

Factors that determine torque

• Force applied: Torque is directly proportional to force, so applying more push creates greater turning force.
• Distance from the axis: Torque increases as the distance from the axis of rotation increases, which is why handles on doors and grinding stones are placed near the outer edge.
• Angle of the force: Pushing at a perpendicular 90-degree angle produces the maximum torque, while pushing parallel to the surface produces zero torque.

Calculating torque

The formula for torque, represented by the symbol tau, is force multiplied by distance multiplied by sine theta. For example, a 10 Newton force applied at a distance of 0.5 meters and an angle of 60 degrees produces 4.3 Newton meters of torque to turn a nut. Curling the fingers of the hand in the direction of the force causes the thumb to point in the direction of the torque. Rotating an object anti-clockwise is treated as positive, while clockwise rotation is treated as negative.

How a couple works

A couple uses two equal forces acting in opposite directions, and its formula is force multiplied by the distance between the two forces multiplied by sine theta. Jar lids are designed wide so that the larger distance between the two hands creates a stronger couple, making the lid easier to open. Bottle caps are made small so the distance between forces is short, keeping them tight and preventing liquid from spilling.

Everyday applications

Engineers use the science of torque and couple to design moving machinery. Common examples include turning a bicycle chain, the movement of pistons inside an engine, and the shifting of gears.