The weigh scale is based on the principle that a spring always stretches in proportion to the weight attached to it. A spring is used as a weighing scale. It is a very simple to make a weigh scale.
Things Required : We need a piece of wood about 15 inches x 6 inches x 0.5 inches, small screw, glue, adhesive tape, a cutting board, a spring, small saucer, ply board of about 12 inches x 0.25 inches thick, large screw hook, small screw hook, card strip, adhesive tape, glue, vise and scissors, a cutting board and strings.
Experiment : Drill a hole along the midline from each end of the wood. The hole should be of about one inch. Fix the screw hooks in both the holes. The large hook has to be fixed into the edge on the six inches of the board. Next, take the string and cut it into three, each one should be 15 inches. Tie them together at both ends. Place the saucer in between the strings. It should be so placed that holding the string at the other end lifts it off. Another six inches long string is to be tied to the end where the saucer can be lifted. Next fix the spring from the small screw hook.
The free end of the short string is then passed from the cradle through the small spring on the other end of the board and tied to the free end of the spring tightly. One ply board strip is then pasted on one side of the spring and a card pointer is attached to the bottom of the spring.
The weighing scale is ready. Now, hold it vertically from the hook on the top. Mark a zero where the pointer stands with the empty saucer. Put a 100 gms weight on the saucer and mark where the pointer stands at 100 gms. Add 100 gms weight and again mark. Go on adding weight and marking the pointer. The weigh scale is now complete. One can take weight of many things using the scale.