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 During the experiment the only factor that I will change will be force applied (by the 100g masses given) to the elastic band. The different weights that I will be using will be: 100g, 200g, 300g, 400g, 500g, 600g, and 700g. The variables that will stay constant will be: 1) The height of the clamp from the table to the floor. 2) The same elastic band will be used. 3) The same staple will be used. 4) The same distance from the elastic band to the ceiling (207cm, this will be the maximum height the staple will reach)
5) The same width of the elastic band while attached to the clamp (5cm) 6) The same equipment will be used eg clamp and stand, ruler etc. 7) The length of the string-8cm Below is the table, which I will collect my data/results in. FORCE (N) EXTENSION (cm) HEIGHT (cm) HEIGHT (cm) HEIGHT (cm) HEIGHT Average (cm) ELASTIC ENERGY (J) Once I have collected the data I will use it to draw a force-extension graph as shown below. If the elastic band obeys Hooke’s law then the results plotted should give us a straight line and then we can find out the elastic energy stored from the area under the graph.
If the elastic band does not obey Hooke’s law then the results plotted will not give us a straight line and so I will estimate the elastic energy stored (area under the graph) using an approximation method. E. g. find the energy represented in one square and count the number of squares. In this case the energy stored: At extension of 0. 1 = area A under the graph At extension of 0. 2 = area A+B under the graph At extension of 0. 3 = area A+B+C under the graph At extension of 0. 4 = area A+B+C+D under the graph Accuracy and Sensitivity.
To maximize the accuracy in the experiment I will take 3 reading for each test and then I will take an average. 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 string between the weights and the elastic band, the extension will stay the same and I will have time to get into the right position to measure the height of the staple. This method is more accurate and will give me more reliable results. When doing the experiment the 2 meter rulers will be stuck with some blue-tack on the wall opposite to the stand/clamp on the table. I will sit on the table behind the stand and clamp lining myself with the 2-meter rulers so when judging the height of the staple when fired is easier and I can get a more reliable and accurate results.