# I am doing an investigation in to how much a metre rule bends when one end is clamped to a table and a varied load is attached to the other end that hangs off the table, thus bending the rule.

Tom Owens

Set 5

Physics Sc1

The Plan:

Simple procedure:

I am doing an investigation in to how much a metre rule bends when one end is clamped to a table and a varied load is attached to the other end that hangs off the table, thus bending the rule. I shall take relevant readings that I shall repeat three times and record the results in a table.

Hypothesis:

I hypothesise that the greater the load attached to the metre rule, the more the metre rule will be inclined to bend. There are two reasons for this. The first is because ‘the extension is directly proportional to the stretching force.’ This is Hooke’s Law but cannot only be applied to springs, but also to metal wires, girders in bridges, but more importantly anything where the extension will be affected by the load. To see if my prediction is correct I will experiment, and obtain results using Hooke’s Law. He found that the extension is proportional to the downward force acting on the spring. The formula that represents that is:. This is where F = force in Newton’s, k = spring constant and x = extension in metres. I also believe that the amount that my metre rule will bend shall be quantitative. By this I mean that if the load doubles, so will the extension. I believe that if I put on three times the load, I will get three times the extension (and so on until eventually the metre rule cannot hold any more weights and snaps.) This shows that the extension is directly proportional to the stretching force. Therefore I will choose the following loads: 100g, 200g, 300g, 400g, 500g, 600g, 700g, 800g, 900g, and 1000g. This will make it easy for me to tell whether my results will be quantitative and it is unlikely that the metre rule will snap with only 1000g as the maximum load. If the rule did snap, we could say that it had gone passed the elastic limit, which means that if something is bent beyond this point, in the case of the metre rule, it would snap and not be able to return to its original shape. Hooke’s law can only be applied up to the limit of proportionality as after this, permanent damage is done to the metre rule. It no longer obeys Hooke’s Law as equal increases in stretching force produce larger increases in extension than expected.

The second reason is that gravitational potential energy acts on the increasingly heavy masses and draws them towards the floor. The heavier the mass, the greater the gravitational pull as mass (kg)  g (N/kg)  change in height (m) = change in gravitational potential energy (joules). As height remains constant and (g) on earth is 10N this means that only the mass varies. Therefore if the mass is 100g (0.1kg), g is 10N on earth and height is always 90cm (0.9m), then change in gravitational potential energy = mass x g x change in height = 0.9 joules. But if (g) and height remain constant and the mass becomes 1000g (1kg) then the gravitational potential energy = 1kg x 10N x 90cm (0.9m) = 9 joules. This also proves that the greater the mass, the more the rule will be inclined to bend as there is a greater change in gravitational potential energy making the heavier masses more inclined to fall to the ground.

My Pre investigation Plan:

I have done a pre investigation plan so that I now have a much clearer picture of what I am going to investigate when I actually collect my results. It gives me an incite in to the investigation. I set up the experiment with the necessary apparatus and took one set of readings. When I collect the results for my proper investigation I shall repeat the results three times so as to identify any anomalies and make sure that all my results are quantitative, thus obeying my hypothesis. This will also allow me to calculate the averages and the range, to make suitable graphs. It was unnecessary to repeat my readings for my pre investigation plan as I was only getting a feel of what I was going to do. I collected my results in the table below:

These results show that my hypothesis is correct, as they are quantitative, e.g. when the load is 400g the extension is 8.5cm, and when the load is 800g the extension is 16.7 cm. I can see that the extension is almost doubled when the load is doubled which proves that my results are quantitative. Even in the pre investigation plan this show us that the extension is directly proportional to the stretching force and proves that Hooke’s Law is correct. In my pre investigation plan I also found out that the metre rule that went vertically upwards from ...