, Research Paper

Physics Coursework:-

Bridges. Plan.

Aim: -

The aim of this experiment is to find out the amount of sag a bridge of different lengths can cause when under different kinds of tension and mass. Apparatus: -

To carry out this experiment we will need the following apparatus -

Weights (In different proportions)

A measuring apparatus (Ruler)

1 metre of wood

Two wooden blocks.

Method: – We will assemble the apparatus together and set the pieces up as shown in fig.1. The two wooden blocks shall act as the supports and the material will be the main beam linking the two blocks.

We shall place the material across the blocks. We shall measure the length from the bottom of the beam and floor using a ruler (in centimetres). We shall have the length of the actual bridge at 90 cm, then 70cm and 50cm (fig2) if so we shall use the measurements in between the stated for further knowledge. We shall place different amounts of weights onto the centre of the bridge so we can measure the maximum sag it causes. The weights shall increase at 50g intervals or at 0.5N until we reach to 500 kg or 50N (Mass = 10 / Weight on Earth). So we are looking for 10 results and that should enough to draw a suitable graph.

We shall then be able to measure the sag, which is caused by the mass on the main beam using a ruler; we shall measure the sag from its lowest point to the floor (fig.3). We shall repeat the experiment for the same weight times so we have an accurate reading, if the measurements are not all the same then we shall take the resulting average. We will have to be safe that the beam does not snap especially the in case shards fly out so will be taking minor precautions and shall not be adding ludicrous amounts of weight onto the beam.

There will be a number of factors that can or will affect the experiment.

ØThe Measurements –

The measurements that we shall take must be fair or the results shall not be accurate. The ground or the floor on which we measure to must be even or the measurement will be inaccurate, the ground should not have any large cracks or crannies in which the ruler can set into or there will be inaccuracies. If the ruler cannot be able to measure the sag then we shall use a string as necessary.

ØThe Equipment –

The equipment that we shall be using will be checked to see if there is anything wrong with it, for example the main beam already has a sleight bend within it or if the blocks are uneven. We shall a bottle full of water to check if the floor is even etc. We will have to use the most accurate equipment available to us so we can obtain the best possible results.

The material that we are using as the main beam we be one metre in length otherwise the sag we not be the same proportion and will also be a regular shape (length, height, width) or again the sag will not be proportion to each other. The materials will have an equal variable 1.5 cm overlap on both sides on the blocks to stabilise the beam. Planning Help: –

My plan is a sophisticated plan because it has a lot of controlled factors and variables that are suited if anything in the plan goes wrong. The different materials will give us a good understanding in the different amount of tension is caused when the materials molecules is under tension, as using concrete as an example many people think it is strong but it is actually weak when under tension! The amount of measurements that we will make will help draw a graph which we can understand and see any mistakes. The experiment of Hooke’s Law (= The extension is directly proportional to the force) in which we used springs also corresponds to this experiment. The object will extend until it reaches

‘ The Limit Of Proportionality’ and then the object will become deformed. I have researched from textbooks and the Internet to help in my planning.Prediction: –

I predict that the largest bridge length will sag the most due to the fact that the supports are further away and thus gravity plays a little part and also there are more of the molecules not being supported and thus will stretch more than the other measurements. I predict that the sag the different lengths cause will decrease in a noticeable pattern; I predict this because in the experiment with the springs we noticed that the extension went up in pattern, (directly proportional to the force) and thus the same will happen in this experiment but the length of the bridge will determine the length of the sag when the different weights are placed on top it.

Results: – We gathered our results and placed them into a table and onto a line graph. (On extra pages.) Explanation Of Graphs – The 3 main graphs are the line graphs of the 90, 70 and 50cm spans. These show a proportion, that the more mass on the bridge the higher the amount of sag that occurs, which is Hooke’s Law. The straight line of best fit within the graph shows this. Conclusion: – I conclude that my prediction that shorter the span of the bridge then the lower sag it will produce was correct. We noticed a pattern in the amount of sag that reduced in every span. 90cm span – The sag increases by 0.2cm every 100kg.

80cm span – The sag increases by 0.15cm every 100kg

70cm span – The sag increases by 0.1cm every 100kg

60cm span – The sag increases by 0.1 or 0.05cm every 100kg

50cm span – The sag increases by 0.05cm every 100kg

From these results we can potentially predict the amount of sag that will occur at every length of span, if we had an extremely accurate measuring instrument.

My prediction matched the result due to an experiment on Hooke’s Law which we conducted previously and because the two where connected we could roughly see what the results were supposed to be.

I also did some research using the Internet and found out the formulae for Hooke’s Value, this is used for checking proportions. Hooke’s Value = Mass

Extension In the graph and the tables that have been drawn the value is equal for each of the weights and this shows that the proportion between the weight and the extension is correct.

Evaluation: – The experiment worked out to produce good and accurate results so we could plot a graph and draw a sensible conclusion.

The results obtained were accurate enough but the was a few amorous results obtained when experimenting the span of 60cm this is most likely due to the fact that the measurement that was required was too small to be measured by a standard ruler of 15cm.

70cm span – The sag increases by 0.1cm every 100kg

60cm span – The sag increases by 0.1 or 0.05cm every 100kg

50cm span – The sag increases by 0.05cm every 100kg As we can observe here the sag is decreasing at a steady amount but when we reach 60cm the progress is stopped so the increase of the sag could be 0.75cm and we need an instrument capable of going into minute measurements or it could be that the measurements taken at the time were not taken properly and thus need to be retaken.

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