Biomedical Engineering Reference
In-Depth Information
Chapter 2
Torques
Torque exerted by a force is an important physical quantity in our daily life. It is
associated with the rotation of a body to which a force is applied, unlike the force
that is related to translation. For a body to be in rotational equilibrium, the sum of
all torques exerted on it must be zero.
2.1 Objectives
To discuss the concept of torque
To obtain the torque due to more than one force
To establish the conditions for rotational equilibrium of a rigid body
2.2 Concept of Torque
Torque or moment of a force,
M
F
, is a physical quantity associated with the
tendency of a force to produce rotation about any axis.
Torque is a vector quantity, but, in this topic, we will use it as a scalar,
introducing a sign convention that will allow us to add algebraically several torques
due to the forces applied on a body. The sign of torque is taken to be positive (+) if
the force tends to produce counterclockwise rotation and negative (
) if the force
tends to produce clockwise rotation about an axis.
The effect of rotation depends on the magnitude of the applied force
F
and on the
distance
d
⊥
(perpendicular) to the axis of rotation. Torque is calculated by the
product of the magnitude of force by the distance (
d
⊥
) from the line of action of
force
F
to the axis of rotation. The line of action is the straight line, imaginary, that
determines the direction of the force vector. The distance
d
⊥
is called the moment
arm or the lever arm of the force
F
. The segment that defines the lever arm is
perpendicular to the line of action of the force and passes through the axis of
rotation. The magnitude of the torque,
M
F
, is defined by (
2.1
):
