Forces in Equilibrium

Vectors in Equilibrium

When 3 vectors are in equilibrium, the resultant vector = 0. After joining all the vectors tail to head, the head of the last vector will join to the tail of the first vector.

Forces in equilibrium

Forces are in equilibrium means the resultant force in all directions are zero.
When the forces acting on an object are balanced, they cancel each other out. The net force is zero.

Effect :
  • an object at rest is continuely at rest [ velocity = 0]
  • a moving object will move at constant velocity [ a = 0]


Diagram above shows a load of mass 500g is hung on a string C, which is tied to 2 other strings A and B. Find the tension of string A.


Tension of string C, TC = weight of the load = 5N
All forces in the system are in equilibrium, hence

Vertical component of tension A (TA) = TC
TAcos60o = TC
TA = TC/cos60o
TA = 5/cos60o = 10N

External Link

Interactive Animation
Newton's third Law of Motion - Java Applet