Problem I have been asked to investigate the stresses and strains on the Queens bridge caused by traffic. Hypothesis I predict that as the mass increases the sag on the bridge will increase as well, thus obeying Hookes law. Variables The span of the bridge The thickness of the bridge The width of the bridge The material that the bridge is made of The mass put on the bridge Apparatus Pen Paper 2 G clamps Boss and clamp Sand bucket 2 Metre rulers Pointer 2 Stools Boss head Retort stand 10 x 100 g Masses Fair Test To make it a fair test i will keep: The span of the bridge same ruler metre Safety Clamp metre rulers to the stools so that they do not fall Set a sand bucket directly under weights so that if they fall they will do so into the bucket Sellotape weights to the ruler so they dont fall Observations / Measurements I will measure the weight on the bridge two times for each mass and average them to make it accurate. I will add 200 g each time, which will give it a better depression then 100 g making my experiment more accurate.
I will do this up to 1 kg, but no more as larger masses may break the metre ruler. I will measure the sag in mm using a metre ruler. Strategy I will display my results in table and then into a graph of depression against mass. Scientific Explanation the particles in a solid are packed closely togeetherand therefore there are strong forces of attraction between them. Forces of attraction are weakened when tensile forces are acting this is what causes the Queens bridge to sag, if the tensile forces were removed the forces of attraction in between the particles would be stronger and they would move closer together provided you dont go past the elastic limit. Scientific Knowledge Hookes law states that the extension of a spring is proportional to the force provided it does not go past its elastic limit.
Method I will set up the apparatus as shown in the diagram below. I will keep the metre ruler with no mass on it and take the initial reading. I will place a 200 g mass on the metre and take the reading of how much the ruler has staged. I will take off the mass and place it on again and record the reading again. I will do this twice to ensure accurate results and a fair test. Iwill repeat this for 200 g, 400 g, 600 g, 800 g, and 1 kg.
I will take an average of all the readings to put them in a graph. This is a diagram of how to set up the apparatus. Table of results Trends I noticed that each time i added 200 g, the sag increased by 2 mm. Conclusion From my table of results i can see that my prediction was correct. My hypothesis was that as the mass increased the sag would increase as well. My graph was a striaght line passing through the double zero.
The sag was directly proportional to the mass and didnt pass the elastic limit. Evaluation I do not think that i need to improve my experiment in any way because my results were all in a striaght line which proves my results were accurate.