Torque

Torque applied via an adjustable end wrench

Relationship between force, torque, and momentum vectors in a rotating system

In physics, torque is the tendency of a force to turn or twist. If a force is used to begin to spin an object, or to stop an object from spinning, a torque is made.

The force applied to a lever, multiplied by the distance from the lever's fulcrum, multiplied again by the sine of the angle created, is described as torque. This is also known as "r cross f," or "force times fulcrum distance times sine theta."

Fulcrum

Fulcrum is the axis of rotation or point of support on which a lever turns in raising or moving something.

Equation

The equation for torque is:

[math]\displaystyle{ \boldsymbol \tau = \mathbf{r}\times \mathbf{F}\,\! }[/math]

where F is the net force vector and r is the vector from the axis of rotation to the point where the force is acting. The Greek letter Tau is used to represent torque.

The units of torque are force multiplied by distance. The SI unit of torque is the newton-metre. The most common English unit is the foot-pound.

Torque Media

• 

  A particle is located at position r relative to its axis of rotation. When a force F is applied to the particle, only the perpendicular component F⊥ produces a torque. This torque τ = r × F has magnitude τ = = sin θ and is directed outward from the page.

• 

  Diagram showing moment arm.

• 

  The torque caused by the two opposing forces Fg and −Fg causes a change in the angular momentum L in the direction of that torque. This causes the top to precess.

• 

  Torque curve of a motorcycle ("BMW K 1200 R 2005"). The horizontal axis shows the rotational speed (in rpm) that the crankshaft is turning, and the vertical axis is the torque (in newton-metres) that the engine is capable of providing at that speed.

Other websites

• "Horsepower and Torque" Archived 2007-03-28 at the Wayback Machine An article showing how power, torque, and gearing affect a vehicle's performance.
• a discussion of torque and angular momentum in an online textbook Archived 2010-12-14 at the Wayback Machine
• Torque and Angular Momentum in Circular Motion on Project PHYSNET.
• An interactive simulation of torque