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# Find the efficiency of energy conservation of a staple fired by an elastic band.

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Introduction

Harwinder Kalirai

Physics coursework

## Aim

Find the efficiency of energy conservation of a staple fired by an elastic band.

## Apparatus

2 clamps

2 G- clamps

Elastic string

Staple (2g)

2 Rulers (m)

Weights (N)- 100g masses

Blue-tack

Goggles

String

## Theory

Energy conservation: in any process, energy can be transferred but cannot be created or destroyed. There are two types of energies, potential energy (elastic stored energy) and kinetic energy.

Elastic bands have a rest length in which they are in a normal state, having zero elastic energy stored.

When they are stretched they are deprived of their normal state and become storage of elastic energy. Elastic bands have a natural tendency to want to return to there rest state and thus resist being stretched. It is the resistance that provides the elastic energy.

When you release the band it snaps to its original length. This stored elastic energy has been changed to kinetic energy. This provides a force that is strong enough to push the staple into the air, so the staple gained potential energy.

Elastic energy                       Potential energy

In this particular experiment stretching the elastic band to find the efficiency of energy transfer of a staple fired by an elastic band.

To find the efficiency of the energy transfer to the staple I will use the equation;

Efficiency = mgh   *  100

Area

To calculate the potential energy gained by the staple I will use the equation:

Potential energy = mg h                 (g = 9.81)

## Variables

Middle

I will also be using equipment, which is accurate and give me reliable results.

I will use an electric weighing machine that weighs to every gram. I would use this to measure the staple.

I will also use two one-meter rulers, which I will measure the height of the staple when fired. I will measure to every 5cm because when the staple is fired it will be to quick to get a precise height of the staple but I will repeat the same test 3 times.

I will also be using an 8cm piece of string to attach it onto the weight holder and the elastic band. So when the elastic extends I can place the staple on the elastic and when in position to measure the height of the staple I will cut the string and the staple will be fired into the air and I will measure, I will do this for each test.

I decided to use the piece of string instead of holding the elastic band with my fingers and then taking the weights of with my other hand. This is because holding the elastic band at a specific extension with my fingers could increase or decrease the extension and so would effect my results very much. Using a

Conclusion

Another reason could be that when stretched, energy could of been lost as a form of heat. When the elastic band is stretched the rubber polymer chains become more orderly and H bonds form between these chains. This H bond formation is exothermic therefore the stretched elastic band will feel warm and heat will be lost.                                               (Reversing this process (when unstretched), the polymer chains become disorderly, the H bonds break and as this is endothermic, heat is absorbed and the band feels cool.) This heat energy lost will have an effect on the transfer of energy between the elastic band and the staple.

To keep this experiment as accurate as possible I took 3 reading for each test and then I took an average. I used appropriate and reliable equipment and used them properly.

When taking the results I will also draw the graph at the same time so if any chance an anomalous result does occurs I can go back and repeat the same test to get the right result. I also design the experiment so I would be as accurate as possible using the equipment from the lab.

I thought that the experiment went well, the results that I got I thought was accurate and reliable. I thought that the experiment was well planned, reducing any factor that would lead to unreliable results.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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