Question

What is the first condition of equilibrium?

Answer 1

The vector sum of the forces acting on an object is equal to zero. This is known as static equilibrium. This is also in all directions.
\[\sum_{}^{}F _{x}=0\]\[\sum_{}^{}F_{y}=0\]and any other directions being accounted for.

Answer 2

Don't forget rotations! The vector sum of all forces acting on a body must be equal to 0, but to avoid rotations, the vector sum of all torques caused by those forces about any point must also be zero. If you want static equilibrium, then the vector velocity of the object relative to the reference frame must also be zero. In other words, no translations and no rotations

Answer 3

Well, she said the first condition of equilibrium, not the second.

Answer 4

the VECTOR summation of ALL the forces must be equal to zero