Everything Science Grade 11

CHAPTER 12. FORCE,MOMENTUM AND IMPULSE 12.3

As an example of an object in equilibrium, consider an object held stationary by two ropesin the
arrangement below:

50 ◦ 40 ◦

Rope 1 Rope 2

Let us draw a free bodydiagram for the object.In the free body diagramthe object is drawn as adot
and all forces acting onthe object are drawn inthe correct directions starting from that dot. Inthis
case, three forces are acting on the object.

�

50 ◦

40 ◦

Fg

T 1

T 2

Each rope exerts a forceon the object in the direction of the rope away from the object. These tension
forces are represented by T 1 and T 2. Since the object has mass, it is attracted towards the centre of the
Earth. This weight is represented in the force diagram as Fg.

Since the object is stationary, the resultant forceacting on the object is zero. In other words thethree
force vectors drawn tail-to-head form a closed triangle:

50 ◦

40 ◦

Fg

T 1

T 2