5.3 Torque

Identify the torques exerted on a rigid system.

• T orque results only from the force component perpendicular to the position vector from the axis of rotation to the point of application of the force.
• The lever arm is the perpendicular distance from the axis of rotation to the line of action of the exerted force.

Describe the torques exerted on a rigid system.

• T orques can be described using force diagrams.
  • i. Force diagrams are similar to free-body diagrams and are used to analyze the torques exerted on a rigid system.
  • ii. Similar to free-body diagrams, force diagrams represent the relative magnitude and direction of the forces exerted on a rigid system. Force diagrams also depict the location at which those forces are exerted relative to the axis of rotation.
• The torque exerted on a rigid system about a chosen pivot point by a given force is described by
  • i. The cross -product between two vectors, A and B, results in a vector quantity of magnitude
  • ii. The direction of the vector resulting from the cross-product of vectors A  and B  is perpendicular to both vectors A  and B  and therefore is normal to the plane defined by vectors A  and B  .
  • iii. The direction of the vector resulting from the cross-product of vectors A  and B  can be qualitatively determined by applying the appropriate right-hand rule.