Question

what is the first condition of equilibrium ​

Answer 1

$The first condition of equilibrium states that for a body to be in equilibrium\\, the vector sum of all the forces acting on that body must be zero.\\ But equation 11.1, the first condition of equilibrium,\\ is just a special case of equation 5.9, Newton's second law of motion$

Answer 2

the first condition of heat equilibrium is that the temperature of the bodies in direct contact should be equal