To use rubber bands to produce an accurate and reliable spring balance to weigh fish caught by an Angler. We have to consider how reliable and sensitive the gauge will be.

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The Anglers Problem

Aim

To use rubber bands to produce an accurate and reliable spring balance to weigh fish

caught by an Angler. We have to consider how reliable and sensitive the gauge will be.

Prediction

I predict that the greater the weight applied to the band, the further it will stretch. This is due to extension being proportional to load, and so if the load increases so does the extension and so does the stretching distance.

I believe that the best device would produce results to form a graph similar to the one below (line of best fit shown in red).

I predict that the two bands in series will be the most sensitive device, due to its length. It will also be more stretchy (blue line). However its elastic limit will not be that high. The 2 bands in parallel will not be as sensitive but it will have a high elastic limit (green line). I believe that the 2 parallel connected to the one band will be a good device. It will be sensitive (due to its length) and it could cope with a heavy load due to the thickness of the top half. The two bands in parallel connected to the two bands in parallel will be both sensitive and strong. This would make the best device.

Hypothesis

Hookes Law states that if you apply force (f) to a spring, the spring will stretch by some length (x). Doubled force means double the stretch. This is known as a mathematically direct relationship. Line of best fit for a force vs. stretch graph would be a straight line ascending steadily, as the weight increases. This is because the amount the spring stretches is directly proportional to the stretching force.

This direct relationship can be represented by the formula: y = mx+b, where m is the slope and b is the y-intercept. So y is the force and m is the spring constant (size of force that stretches spring by 1cm) and b is 0.

So using Hookes Law we can write F= KX (force=spring constant x extension). To find the value of K I will add weights so the band stretches by 1 cm. Using elastic band I will try and replicate the properties of a spring, as this would make the best suited device.

Higher values represent stronger, less stretchy bands, and lower values represent weaker easier to stretch bands.

The only limitation to Hookes Law comes if you stretch the band beyond its elastic limit or, in other words, when you stretch the band so far it permanently deforms.

If the F=KX relationship applies to results gained from a certain formation with the bands, then this is the best device to weight the fish, as it show that the spring is both accurate and sensitive, and that the amount the band stretches is proportional to its stretching force. So if the extension doubles when you double the force, and the band goes back to its original length afterwards, then this is the best formation for the Angler.

For a regular rubber band doubling the weight would more than double the extension. This is due to its elasticity and is why I have to use different formations.

If the bands are in series they will stretch a lot and be very sensitive, due to its length.
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If the bands are in parallel they wont stretch as much, but will cope with more weight. I will use this to create a formation that will use the positive aspects of both, without the negative aspects thus creating the best device.

Rubber bands are polymers. For such a versatile material, it has a very simple structure. A molecule of polyethylene is nothing more than a long chain of carbon atoms, with two hydrogen atoms attached to each carbon atom. Sometimes it's a little more complicated. Sometimes some of the carbons, instead of having hydrogens attached to ...

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