Angle of Repose Lab
From GeoClasses
The objective of this lab is to design an experiment to determine the angle of repose of differnt sediments.
Contents |
Angle of repose
A rock on a flat surface is held down by gravity. To move it you have to exert a force on the rock that exceeds the maximum frictional force that keeps it in place (the critical shear stress)
On a slope there is a component of gravity called the shear stress that acts along the slope to move the rock. This force has to compete against the frictional force. In this example, on a 15 degree slope the shear stress does not exceed the maximum friction (critical shear stress).
At a certain slope however, the shear stress is able to overcome the maximum friction and the rock begins to slide. This is the critical slope. If you tried to make a pile of sand for example, the slope of that pile would be this critical slope, called the angle of repose.
- Typical slopes have angles of repose between 33 and 37 degrees.
 Rock on a horizontal surface. |
 Beneath the angle of repose. |
 Beyond the angle of repose. |
 Diagram demonstrating the angle of repose.]] |
Exercise Part A
Using the sediment samples given to you, create an hypothesis, and design an experiment to determine what controls the angle of repose. If you need equipment that is not present, ask your instructor if they are available.
Designing experiments and peer review
The object of this lab is to get a better understanding of the angle of repose, and of the scientific process. Designing experiments and peer review are important elements of the scientific process.
Example of Hypothesis testing
One hypothesis, which probably would not be a good one, is that the color of the sediment grains determines the angle of repose. (You will need to state what evidence you used to come up with your hypothesis.)
Thus you could design an experiment with samples of differnt colors to determine if color is important. To do this you would need to use multiple samples of sediment that are the same except for their color.
Hypothesis
State your hypothesis. Be sure to mention how you came up with the hypothesis.
Experiment Design
Give complete instructions on how to perform the experiment to test you hypothesis. Your instructions need to be clear enough so that someone could replicate your experiment to confirm your results. Remember, repeated testing is the key to the scientific method.
Observations
Put in the measurements you made while following your instructions. Be clear so that someone reading this can understand what exactly you measured.
Conclusions
Well, did you hypothesis pan out. Why or why not? Explain. Accept, reject or modify you hypothesis based on your results.
Exercise Part B: Peer review
You will now exchange your experiment instructons with someone from another group. We'll call this other person the reviewer. Then each of you will attempt to follow the instructions to replicate the other's experiment.
Name of reviewer
Instruction Detail
Were you able to follow the instructions? Please make detailed comments about what was difficult to follow.
Replicating results
What results did you get from replicating the experiment? Do they agree with the original results?
Validity of experiment
Was the experiment adequately designed so that it could accurately test the hypothesis. Explain why or why not.
Do your results concur with the original results. Why or why not?
Exercise Part B: Response to peer review
In this section, the original author of the experiment gets to respond to the comments of the reviewer. You may respond to each item detailed by the reviewer separately, or altogether.
Based on the reviewer's comments and your response, do you stand by your orignal experimental design and conclusions. (explain why or why not).
Did you find the peer review to be useful? Do you think it benefits the scientific process?
