Experiment
Introduction
Last fall I did a research project on landslides. I wanted to do an experiment on one aspect of landslides, but I was not sure what kind of experiment I could do about landslides. Landslides are too dangerous and unpredictable for a grade 6 student to study, so I talked to my uncle who is a geotechnical engineer. He suggested making an apparatus that could measure the angle at which different rocks slid over one another.
Hypothesis
When an object slides against another object, the type of material and the roughness of the surface changes the angle of the slope when the object begins to slide.
Materials
I used four pieces of wood, a protractor, screws, three different kinds of rocks, and a hinge.
Method
I made a slope out of wood and hinges. Because my slope was hinged I was able to make the slope more or less steep. I attached a protractor to the base of the slope so that I was able to measure the angle of the slope. I collected different types of rock including slate, granite, gneiss, and Gambier formation. I collected the gneiss at the site of the Porteau landslide which occurred in 1969 on Route 99 on the Sea to Sky Highway in British Columbia. My uncle cut several of the rocks with a rock saw so that several of my rock samples had smooth surfaces. He did that so that I would have smooth as well as rough rock surfaces to slide over one another. I put one rock onto the slope. It was supported by a strip of wood so that it was held securely. Then I put another rock on top of the first rock. I made the slope gradually steeper until the second rock slid on top of the first rock. I noted the angle of the slope when the second rock began to slide. I repeated this procedure with the different types of rocks and with different combinations of smooth and rough surfaces. Each time when the rock began to slide I recorded the angle of the slope.
Results
Conclusions
Generally the rocks with smooth surfaces slid at a shallower angle than the rocks with rough surfaces. Different kinds of rocks slid at different angles. When I tested the smooth surfaces of "gneiss" against each other I got one very low result and one very high result. This is because in one position, the bottom rock tilted downward and made it very easy for the second rock to slide. In the other position the bottom rock tilted upward, so it made it very difficult for the second rock to slide. If I had had a flatter sample of rock, I would have got a more accurate result and the angle at which the rock slid would probably have been an average of the two results. I had one piece of "gneiss" which had a natural joint. The top section did not slide until it was tipped at a very steep angle. It fit together so well that it was almost as if the pieces of rock were locked together.