# Principle and use method of spring scale

Spring balance is also called spring dynamometer.
The principle of the spring balance: within the elastic limit, the length of the spring stretched or compressed is proportional to the tensile force or pressure. Writing:
F=k·x
Among them: “F” represents the elastic force of the spring, which is the force applied to the force when the spring deforms.
“X” is the length of the spring that is stretched or shortened. Note that “x” is based on the length of the spring without deformation, that is, x=x’-x0 or x=x0-x’.
“K” is called the stiffness coefficient of the spring. It describes the magnitude of the elastic force generated by the unit deformation. The large value of k indicates that the force required for the deformation unit is large, or the spring is “hard”. k is related to spring material, length, thickness, etc. The international unit of k is cattle/meter.
If several identical springs are connected in series or in parallel, the stiffness coefficient of this new spring is no longer the original stiffness coefficient. Assuming that the stiffness coefficient of two springs with both stiffness coefficients k in series is k1, then F=k1·x. Since the elastic force at point a is also F, the two stiffness coefficients can be written for spring 1. When the springs with the same original length are connected in parallel, the stiffness coefficient is k2, then
F=k2·x
Use of spring dynamometer
Before using the spring dynamometer, you must understand its structure. As shown in Figure C, there are mainly springs, pointers, irons, hooks, etc.
(1) First of all, you must see its range clearly. The force to be measured cannot exceed its range. Because the spring has a certain elastic limit, the measurement will not be accurate if it exceeds this limit, and it may damage the dynamometer.
(2) Before measuring, you must see the division value of the spring dynamometer so as to read during the measurement.
(3) Before measuring, check whether the pointer is pointing at the zero scale line. If it is not pointing at the zero scale line, adjust to make the pointer point at the zero scale line.
(4) Before use, gently pull the hook of the spring dynamometer back and forth to prevent the pointer from being jammed, which may cause larger errors in the measurement.
(5) When measuring, the force of the hook of the tension spring dynamometer should be parallel to the shell of the dynamometer to avoid distortion and friction, and minimize the measurement error due to friction.
(6) Wait until the reading is stable before reading. When reading, the line of sight should be perpendicular to the surface of the scale panel.