Hookes lab

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Siddharth Nair

          10 C

PHYSICS LAB REPORT

VERIFYING HOOKE’S LAW

AIM:

The aim of performing this experiment is to find out if the extension produced by a spring is directly proportional to the tension force applied to it and thus verifying Hooke’s law.

THEORY:

Hooke's law is the relationship between the force exerted on the mass and its position x. Consider a object with mass m, that is on a frictionless surface and is attached to a spring with spring constant k. The force the spring exerts on the mass depends on how much the spring is stretched or compressed, and so this force is a function of the mass's position.

The idea behind Hooke's Law is that any object that is initially displaced slightly from a stable equilibrium point will oscillate about its equilibrium position. It will, in general, experience a restoring force that depends on the displacement x from equilibrium.

The extension or the strain will keep increasing as you increase the weight added as long as the spring doesn’t remain stretched permanently.  A point is reached where the spring can’t stretch any more when more tension force is applied to it and snaps. This is defined as the ‘elastic limit’ of the spring.

The force constant ‘k’ of a spring is the force needed to cause unit extension, i.e. 5cm. If a force ‘F’ produces extension ‘e’ then,

k = F

       e

HYPOTHESIS:

As seen the Hooke’s law states that the extension of a spring is directly proportional to the tension supplied to it. Therefore I predict that as more weights will be added the extension will increase almost proportionately. Therefore I also predict that the graph will be as shown below:

The x axis shows the extension produced by the spring, whereas the y axis shows us the stretching force applied to the spring.

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VARIABLES:

Constant:

  •  The surroundings that mean temperature, wind force, etc.
  • The equipments used in the experiment

Independent:

  • The number of weights put on the spring

Dependent:

  • The extension produced on the spring

APPARATUS:

  • Clamp stand with a stable base.
  • Metal spring with a pointer at the end.
  • Uniform meter- rule.
  • Uniform metal weights of 100g each.

FAIR TEST:

  • It should be made sure that the surroundings are not very breezy so that it is made sure that the spring does not oscillate.
  • The same apparatus should be used always so ...

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They have generally shown good grammar and spelling throughout – with only a few ‘typos’ such as ‘nad’ instead of ‘and’. They have used scientific terms usually correctly, with a few notable mistakes, for example they described the elastic limit as the point where the spring snaps – the elastic limit is actually the point after which the spring undergoes permanent deformation under stress, and so will no longer return to its original shape once the stress is removed. They have at times shown a lack of knowledge about Physics conventions – for example they used 10ms-2 as the acceleration due to gravity, when it is more accurate and customary to use 9.8(1) ms-2 for this figure. They have also laid their report out rather unusually – it is much better to describe the experiment logically and more chronologically, beginning by describing the aims of the experiment and a hypothesis, then a clear diagram and description of method (including ‘fair test’ and ‘safety precautions’ sections), followed by a table of results and graphs. This should be followed by an analysis of results and conclusion, and then some suggestions for improvement. As the author has redone the experiment with these modifications, the second experiment should be written up as before, like a new experiment, then the whole thing concluded by a comparison of the two methods. This would have made the experiment much easier to follow and understand, and is, in my experience, essential for gaining good marks. However, the experiment was directly related to Hooke’s law and was clearly carried out well, which helps to make up for the poor layout.

The author has analysed their results to come to the conclusion that Hooke’s law is true. They have considered causes of uncertainty in their measurements, and used this to suggest improvements in the experiment. However, in their place, I would have continued the experiment up to the limit of proportionality in order to be able to compare the springs better and discuss how Hooke’s law only works up to the limit of proportionality. I would also have calculated the spring constant (the gradient of the graphs) in order to see the effect using two springs had on the results. The author has shown in many places a good understanding of the physics involved, although they occasionally confuse terms, such as extension and strain – extension is the increase in length, whereas strain is extension/original length, which gives a fractional value for the ‘stretch’ of the spring. They have also made some flaws in their analysis such as saying ‘spring 1 is more flexible as it does not produce anomaly results’, which is incorrect – the lack of anomalies shows that the experiment was carried out more accurately, with reduced uncertainties. They have shown their workings for calculating the Force exerted on the string from the masses added, which is very easy to forget to do in the write up of an experiment, but very important.

The author has successfully carried out an experiment confirming that Hooke’s law is true. They have considered the results when two springs were used, although they fail to give an accurate description or diagram of this experiment to show whether these springs were used in parallel or series. They have produced graphs which clearly show the relationship between Force and Extension, although these should have been properly labelled. I would also have added uncertainty bars – at GCSE these may not be essential, but they have already worked out the uncertainties anyway, so may as well add them to the graphs. This would have allowed them to more easily identify any anomalies, although there don’t appear to have been any in their experiment.