Elastic constant of a spring.

Actual experiment.

1. Introduction: The aim of this experiment is to find and measure the elastic constant of a spiral spring.
2. Apparatus:

1. Light spiral spring.
2. A scale pan.
3. A meter rule.
4. 2 Clamps and Stands.
5. 2 Boxes of weight.
6. Light pointer for spring.
7. Stop watch.

(c) Method:

1. Suspend the light spring from the clamp and attach a light pointer to the spring.
2. Set up a fixed vertical meter rule beside the spring using the clamp and stand.
3. Attach a scale pan to the spring, and then add suitable weights, noting the reading of the pointer each time.
4. Do this for about 8 loads on the scale pan.
5. Then remove each weight, and record the reading of the pointer each time.
6. If the spring has not been permanently strained the reading of the pointer will return to it’s original or zero reading when all the weights and the scale pan have been removed.
7. Finally weigh the scale pan.

4. Results:

When loading

1. Mass of scale pan = 0.05kg
2. Zero reading of spring = 140mm.

When off loading:

5. Health and safety precautions:

1. Since you are dealing with weights, ensure that you work in the middle of the table because if you work at the edges they might fall on to your foot.
2. You must also be careful when handling the pointer if you are using a sharp pin. This is because it might penetrate you and eventually get tetanus.

6. Report on Elasticity:

            Forces and weights are often measured by means of spring balance. This was investigated in the 17th century by Robert Hooke.

           He showed that when a spring is fixed at one end and force is applied to the other end, the extension of the spring is proportional to the applied force, provided the force is not large enough to stretch the spring permanently.

           The value of the force to which the extension is such that, on the removal of the force, the spring fails to return to it’s original length and begins to stretch permanently is called the elastic limit.

7. Evaluation:

1. Since I was using plasticine and a pin as a pointer, it was a bit difficult to get a perpendicular horizontal position for the pin to the meter rule.
2. Also when you add weight on to the scale pan, the spring kept oscillating for some time before coming to rest. I ensured that at all time when I was taking my reading that the spring was at rest, and this made my reading accurate.

6. Conclusion:

(i)     =      kg per meter extension is the mass hung on the spring per meter extension.

(ii) Since the graph is a straight line passing through the origin, the extension of the spring is directly proportional to the tension in the spring that is Hooke’s law.