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Investigating Hooke's Law into thin wires.

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Introduction

Investigating Hooke’s Law into thin wires

Aim

To find out weather or not Hooke’s Law applies to thin wires.

Theory

This is an investigation into Hooke’s Law and how it operates in relation to the thin wires we are going to be testing. the basic equation for Hooke’s Law is F=KX. What this basically means is that the force is directly proportional to the extension. This is shown in Fig 1.1. In the darkly shaded area the material is elastic and thus the Law applies. However, if the external force is too strong, the material can become permanently deformed thus meaning that Hooke’s Law on longer applies. This is represented in Fig 1.1  by the lightly shaded area.

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        The elastic limit - also shown in Fig 1.1 - of a material is determined by the molecular structure of the material. The distance between molecules in a stress-free material depends on the balance between the molecular forces of attraction and repulsion. When an external force is applied, creating stress within the material, the molecular distances change and the material becomes deformed. If the molecules are tightly bound to each other, even for a large amount of stress there will be little strain. If, however, the molecules are loosely bonded to each other, a relatively small amount of stress will cause a large amount of strain.

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Middle

        The experiments will have to be repeated in order to obtain more accurate results. I have decided that three is a good observation range and should eliminate most errors. The results will differ from one another so I will work out an average.

        The safety of myself and others is very important in the lab. In order to make the experiment as safe as possible I am going to ensure that the following requirement is satisfied:

Everybody must wear safety goggles just in case the fishing wire breaks.  

Apparatus

Thin Wire

Metre Rule

Stand

Clamp

Goggles

Weights

Method

This is an investigation into Hooke’s Law. In order to prove this theory right or wrong I am going to carry out a practical investigation. It will be carried out in the following order:

Place stand on a bench and attach the metre rule using a clamp, ensuring that it is perfectly vertical.

Cut piece of fishing wire about 60-75 cm in length.

Attach the wire to the clamp, leaving a loop at the bottom in order to hang the force.

Measure the length of the again.

Start putting on a force.

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Conclusion

        As further investigation the whole experiment would have to be done again using the horizontal method. Another possibility is that instead of testing one, or the same, material other materials could be tested. For example 32swg copper wire or nylon. This would give a broader understanding of materials which behave in accordance to Hooke’s Law. Different materials could also be compared so that it can be understood whether or not all materials behave in accordance to Hooke’s law. The materials that could be compared are copper wire, rubber and nylon fishing wire.

        Apart from the material and the accuracy, there are other ways of conducting further work into Hooke’s law. The other two variables that could be changed are the thickness of the wire and the length of the wire to begin with - when it has no strain. The thickness would have to be just right so that the wire does not take too much of a load to snap but equally does on snap under a fairly lighted load.  

        Another change that could be made in order to gain detailed results is the Force which is being applied. Instead of applying 2N, as in this investigation, ½ N would mean that the results can be studied more carefully. This would also mean that the elastic limit can be pinpointed to ½ N instead of 2N.

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