Define spring balance.

Hint:You can easily reach the solution to this question by trying to recall what spring balance is and on what principle it works upon. Let us help you by sharing the fact that spring balance works by Hooke's Law.

Complete step by step answer:
A spring scale commonly known as spring balance is a type of mechanical force gauge or weighing scale. A spring balance consists of a spring fixed at one end with a hook to attach an object at the other. It works by Hooke's Law, which states, “The force needed to extend a spring is proportional to the distance that spring is extended from its rest position.” Therefore, the scale markings on the spring balance are equally distributed. Remember, a spring balance cannot measure mass, only weight.
Another interesting fact about spring balance is that a spring balance will only read correctly in a frame of reference where the acceleration in the spring axis is constant. This can be proven by taking a spring scale into an elevator, where the weight measured will change as the elevator moves up and down changing velocities. A spring balance may be labeled in both units of force (poundals, Newtons) and mass (pounds, kilograms/grams). But as a matter of fact, only the force values are correctly labeled. In order to cross-check whether the labeled mass values are correct or not, an object must be hung from the spring balance at rest in an inertial reference frame.

Note: Mathematically, Hooke’s law for a spring balance can be written down as:
$F = - kx$
Where $F$ is the restoring force,
$k$ is the spring constant of the spring balance and
$x$ is the displacement from the rest position of the spring balance.
This formula is extremely useful in other chapters too, like Simple Harmonic Chapter, Newton’s Laws of Motion, etc.