When is the body said to be in static equilibrium?

When is the body said to be in static equilibrium?

Options:

a. when the vector sum of the forces acting on the body is zero

b. when the vector sum of the moments about any arbitrary point is zero

c. when if the body is at rest, it tends to remain rest and if the body is in motion, it tends to keep the motion

d. all of the above

Correct Answer: d. all of the above

Explanation:

The body is said to be in static equilibrium if it remains in its state of rest or remains in its state of motion. When a body is in static equilibrium the vector sum of forces acting on the body is zero as well as the vector sum of the moments about any arbitrary point is also zero.

Mathematically,
In the static equilibrium,
ΣF = 0
ΣM = 0

The study of static equilibrium is applicable in the machines where the movements are relatively low, such as hand operated tools like plier, cutter etc. It is applicable in lifting cranes also.