Torque is defined as the twisting force necessary to support a 1-lb weight on a weightless horizontal bar, 1 ft from the fulcrum.

• A. The twisting force necessary to support a 1-lb weight on a weightless horizontal bar, 1 ft from the fulcrum.
• B. The amount of linear force along the bar.
• C. A measure of rotational speed.
• D. The vertical load at the fulcrum.

Answer: (A)

Torque is the rotational effect a force has about a pivot, essentially the twisting moment you must apply to keep something from turning. It equals the force times its perpendicular distance from the pivot (the lever arm). Here, a 1-lb weight acts 1 ft from the fulcrum on a weightless, horizontal bar, and the force is perpendicular to the bar, so the twisting force needed to hold it is 1 lb × 1 ft = 1 ft-lb. That matches the described idea of “the twisting force necessary to support a 1-lb weight on a weightless horizontal bar, 1 ft from the fulcrum.” The other options don’t describe torque: it is not a linear force along the bar, not a measure of rotational speed, and not the vertical load at the fulcrum (the latter is the reaction force at the pivot).