The rigidity is an ability of a detail or design to counteract the external force applied to it, whenever possible keeping the geometrical parameters. The main characteristic of rigidity – rigidity coefficient.

## It is required to you

- - spring spring;
- - cargoes with a certain weight;
- - ruler;
- - notebook for records;
- - calculator.

## Instruction

1. Present that you decided to build the hands the cargo cart for the motorcycle or the car to take out garbage from the yard, to bring from the field a harvest and so on. It is desirable that the cart was on springs. If you have springs, and you know their coefficient of rigidity, you can calculate what weight they are capable to bear cargo. The coefficient of rigidity can also be calculated by practical consideration.

2. Various springs are intended for work on compression, stretching, torsion or a bend. At school at lessons of physics of children learn to define coefficient of rigidity of the spring working for stretching. For this purpose on a support the spring in a free state is vertically suspended. One of pupils by means of a ruler measures its length. And the result registers in a notebook as L 1 = …

3. Then by the lower end the cargo of a certain mass, for example, of 0.1 kg is suspended. It influences a spring, stretching it, with a force of 1 Newton (1H). The workmate measures the turned-out length of the stretched spring. The testimony of L 2 which, naturally, will be big also registers in a notebook as L 2 = … The size of stretching of L is simple arithmetic action of L 2 – L 1 =.

4. On Hooke's law: Ex. F = kL. Therefore, to find coefficient of elasticity (k), it is necessary to divide force of stretching of a spring (F) into the size of lengthening (L). k = F/L.

5. By practical consideration to define coefficient of the elasticity prepared by you for the spring cart it it will be necessary to squeeze. This work is much more complex carried out in school laboratory. First, measure spring length in a free state and write down result (L 1).

6. Establish a spring vertically in some sleeve, having left free a small top part. Take a certain cargo, for example, gymnastic weight 16, 24 or 32 of kg. Install it on the top face of a spring and note on a sleeve or directly measure by a ruler length of the compressed spring (L 2). Carefully remove the weight.

7. Calculate value L as a difference: L 1 - L 2. Substitute values in already known formula k = to F/L. Select for formula F = kL the admissible mass of the transported cargo, proceeding from the size of compression of a spring.