Relationship between force (F), torque (τ), and momentum vectors (p and L) in a rotating system.

Torque – anything that causes another object to spin.

Torque is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Torque is a measure of the turning force on an object. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque (turning force) that loosens or tightens the nut or bolt.

Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotation. Just as a force is a push or a pull, a torque can be thought of as a twist to an object.

Torque in action

  • Torque, center of mass (video 4:29) – explains the laws of physics as they apply to the player who stays the lowest and masters the concept of torque – which is the tendency of a force to make an object rotate around an axis.
  • opening a door, playing on a teeter-totter, riding a Ferris wheel, and using a wrench or screwdriver – forces are applied to rotate an object. This is “turning force” or torque.
  • walking – as our thighs rotate about a ball joint in our hips, our muscles are applying torques to our legs

Tractor Pull (video 4:30) – 850hp diesel vs. 18hp steam tractor. Just because it is old, doesn’t mean it won’t work, or has to be retired. It’s all about torque and traction.

  • traction
  • horsepower

Engineering ideas

  • force, torque, momentum vector, center of mass, moment, inertia, lever arm, axis, fulcrum, pivot, load, traction, horsepower

Do it
Here are some challenges for you to work on…

  • List at least 2 examples in which torque is used in daily life
  • Describe how offensive linemen use the concept of torque to their advantage
  • Choose 4 different “Lever Arms of the Applied Force”. For each, find out how many pennies it takes to just lift the load pennies. Record the information and calculate the applied clockwise torque in each case. Need 20 pennies, a ruler and a pencil. …activity

Learn more…