2. Moment :
โข The Moment of a force is a measure of its tendency to cause a body
to rotate about a specific point or axis. This is different from the
tendency for a body to move, or translate, in the direction of the
force. In order for a moment to develop, the force must act upon the
body in such a manner that the body would begin to twist. This
occurs every time a force is applied so that it does not pass through
the centroid of the body. A moment is due to a force not having an
equal and opposite force directly along it's line of action.
3. Elements of a Moment
โข The magnitude of the moment of a force acting about a point or axis
is directly proportinoal to the distance of the force from the point or
axis. It is defined as the product of the force (F) and the moment arm
(d). The moment arm or lever arm is the perpendicular distance
between the line of action of the force and the center of moments
โข Moment = Force x Distance or M = (F)(d)
4. Moments
Calculate M on point C : Solve
โข (100 pounds)(12 in) = 1200
pound-inches
โข (200 pounds)(0 inches) = 0
pound-inches
โข 1200 pound-inches + 0 pound-
inches = 1200 pound-inches
7. Couple
โข The moment produced by two equal, opposite, and noncollinear
forces is called a couple. Couples have certain unique properties and
have important applications in mechanics.
Assignment Problem : 57,59
8. Resultants
โข The resultant of a system of forces is the simplest force combination
which can replace the original forces without altering the external
effect on the rigid body to which the forces are applied. Equilibrium of
a body is the condition in which the resultant of all forces acting on
the body is zero. This condition is studied in statics. When the
resultant of all forces on a body is not zero, the acceleration of the
body is obtained by equating the force resultant to the product of the
mass and acceleration of the body. This condition is studied in
dynamics. Thus, the determination of resultants is basic to both
statics and dynamics.
