Practice make Perfect Pracs!

Experiments or Practical Activities (called pracs for short) are a critical part of school science, not (just) because they are fun, but because they form the basis of science in the world. Theories are one thing (and an important part of science) but they are dependent on experiments – without the proof that real world experiments provide, theories would be nothing more than opinions – and have no more validity for understanding the world than any number of other belief systems.

The scientific method developed in ancient Greece, but has continued through a great deal of  “western” science. The basic idea behind the scientific method is that nothing is ever proven conclusively and forever. This means something different than most people interpret it to mean – not that nothing can ever be known (after all ideas like evolution are almost universally accepted amongst the scientific community), but that any theory is always subject to challenge if new information or evidence is uncovered – there is no precedence of authority or ranking. Anyone can look into a theory, and if they find evidence that would seem to challenge the prediction of a theory, present that evidence to the world and the scientific community for evaluation – and if others confirm the evidence, the theory that it challenges may be reconsidered. If the required change is significant enough, it is called a paradigm shift. The most classic example of a paradigm shift is Einstein’s update of Newtonian dynamics to take speeds approaching light  into consideration.

Regardless of what the data is, the development of theory is dependent upon the accuracy and precision of these measurements. Accuracy is how closely the measurements reflect the actual object being measured, Precision is how closely the individual measurements are grouped. Imagine the situation that a group of six people are estimating the height of a tree (which is later measured to be 2.46 m tall) . They make the following estimates:

2.1m, 2.9m, 3.0m, 2.3m, 2.8m, 2.8m

These estimates are neither precise nor accurate. Another group guesses:

2.7m, 2.6m, 2.8m, 2.75m, 2.8m, 2.7m

These estimates are not accurate, but are precise. A final group guesses:

2.4m, 2.45m, 2.35m, 2.4m, 2.3m, 2.5m

These estimates are both accurate and precise. Can you imagine a set of measurements accurate, but not precise?

Measurements can be off for any number of reasons, but there are two main categories of error:

1. Systematic Error: this is the error that results from poor experiment design or poor choice of measurement strategy.

Here is an example of systematic error – if you were measuring air temperature, you want to position your thermometer in a way such that it is not being affected by other heat sources (such as hot asphalt, aircon exhausts, or BBQs)  unlike the thermometer below:

Lots of other examples of poorly sited instrumentation at the surface stations website

2. Random Error: Errors due to inaccuracy in measurement – when repeated measurements of the same phenomenon show different results.

OK, on to the videos:

Another good video.

WordPress doesn’t support playlists, so you can view the rest of the videos here.

See you in class.

Explore posts in the same categories: General Science, Physics

Tags: error, experiment, scientific method, uncertainty

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