Chapter 6: Concurrent and Parallel Forces
(Ewen et al. 2005)
Objectives:
•Analyze equilibrium in one dimension.
•Analyze concurrent forces using force diagrams.
•Distinguish between compression and tension.

Equilibrium is a state of a body in which
there is no change in its motion.
 Object is not accelerating, either at rest or moving
at a constant velocity.
 Net force is zero (Fnet = SF = 0)

The study of objects in equilibrium is called
statics.

A cable supports a large crate of weight 1250 N.
What is the upward force on the crate if it is in
equilibrium?

Four persons are having a tug-of-war with a
rope. Harry and Maria are on the left. And
Juan and Jill are on the right. Maria pulls with
105 lb, Harry pulls with 255 lb, and Jill with
165 lb. With what force must bill pill to
produce equilibrium?

When two or more forces act at a point, the
equilibrant force is the force that when
applied at the same point produce
equilibrium.

In two dimensions, for an object to be in
equilibrium, the sum of BOTH the x- and ycomponents must be equal to zero.
 Fx  0 and  Fy  0

Tension – stretching force produced by
forces pulling outwards on the ends of an
object.

Compression – force produced by forces
pushing inward on the ends of an object.

Two cables supports a crate. The first cable is
positioned at a angle of 00 relative to the
crate. The second cable is at an angle of 120o
and has a tension of 375 lb. Find the tension
on the first cable and the weight of the crate
if the crate is in equilibrium.

A homeowner pushes a 40.0 lb lawn mower
at a constant velocity. The frictional force on
the mower is 20.0 lb. What force must the
person exert on the handle, which makes an
angle of 30.0o with the ground? Also, find the
normal force.

The crane is supporting a crate weighing
6.00 E3 N. Find the tension in the horizontal
supporting cable and the compression on the
boom. Assume the crate is in equilibrium.