Monday, 24 March 2008

How to weigh a dinosaur

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Dinosaurs sometimes left footprints in wet mud or sand, which hardened to leave trace fossils. We can work out how heavy the dinosaur was, if we can compare the footprint with the mark made by a known weight in the classroom. The relationship between pressure, force and area can be used to estimate the mass of a two-legged dinosaur from the area and depth of one of its fossilised footprints.
Do try this out with your pupils and let us have your results.


NTNUES said...

When finding this learning idea, we felt very surprised, because the theorem of this experiment is very easy to catch. Pressure is the only theorem be used, which is defined the force on per unit area or force is equal to pressure multiply area.
But there are more place we can discuss, for example, although we can use the tools that are easy to take in the classroom to complete the experiment and know the result of the experiment in short time in a convenient situation, but the problem would be simplified and the error will be rose. For educational aim, we can still use it to help the understanding of the concept.

There are simple physical concepts be used in this experiment to measure the weight of the dinosaurs. But there are many problems not be up for.
• In this case, we assume that the pressure and the depth of the footprint are in direct ratio. But we think that it is more complicated then our assumption, because of the ingredient of the ‘sand’. It might make the correlation of pressure and depth are not in direct ratio. For instance, you can think about that the rut made by a jeep and the human footprint, the depth of these two things is not in big difference.
• The trace fossils are not formed by sandstone, and it might be another rock. So the result would be affected by rock.
• When we estimate the area of the trace fossils, the error would be produced because of its irregular shape.
• In “follow up the activity” section, it mention that the problem of “how many feet?” For example, the result of walking dinosaurs and standing dinosaurs would be different, even if they were in same depth.
• In the same section of above, the speed of walking or running will made different result.
• Maybe the dinosaur were holding their food in teeth, and this situation would make it different.

Suggestion and direction:
 Do the experiment many times to compare the results.
 Compare the parallel fossils.
 Compare the experiments from different persons.
We can still measure the weight of dinosaurs approximately by using the relationship between pressure and depth. But if we go a step further and combine with other subjects, we might get more in this case. For instance, collecting more footprints and make the result into a synopsis. Maybe we can analysis the activity status of the dinosaurs, like speed and age, and broaden the scope to populations, societies even ecological systems, to make the concept more complete.

ntnues said...

Sorry,We forgot to leave our information.

Bo dong Lin, Hsien lung Cheng, Chia rong Wu, Yi chun Liao, Ting hsiang Huang

Department of Earth Sciences, National Taiwan Normal University.