Biomedical Engineering Reference
In-Depth Information
2.4 Torque Due to Two or More Nonparallel Forces
2.4.1 Resultant of Two Nonparallel Forces Applied
on a Body and Its Line of Action
We have already seen that one of the ways to determine the net torque on a body is
by summing the torques due to each force separately. By another method, we use
the resultant force and its point of application, or better, its line of action and the
correspondent arm.
In the study of torque, it is clear that the point of application of a force is of
fundamental importance. Actually, if the line of action of the force is determined,
the problem is solved, since the arm of the force corresponds to the perpendicular
distance between this line and the axis of rotation.
Observe that the effect of a force on a body does not change if its point of
application is changed, since it stays on the line of action of the force. Using this
property, the resultant force can be determined, dislocating the vectors on their lines
of action to work as shown in Fig.
2.10
for the case of two nonparallel coplanar
(which are in the same plane) forces.
lines of action
F
1
F
2
Fig. 2.10
Resultant force
R
is obtained by the rule of
parallelogram, summing
two forces whose points of
application on the body do
not coincide. Note that the
rule is applied, first, by
dislocating the points of
application of forces to the
same point. The line of
action of the resultant is also
determined by obtaining its
torque about any axis
F
1
R
F
2
