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Thursday, 27 September 2012

Measure for Measure

Any matter in the physical world can be measured. We weigh things, we record temperatures, chart distances and the passage of time, we can determine electrical charges and the amount of force exerted on objects, we are able to calculate the speed of light, describe energy as joules and use candela scales for measuring the intensity of light - and the list goes on and on.

Measurements answer questions about how many, how big, how long, how much? They allow us to make comparisons, make changes and make it possible to describe and record our interesting world. Sometimes it is appropriate to estimate measures or to be 'in the ball park', for example when we might say there are around 20 sweets in a packet or there are about four or five minutes to go before the end of a film. But there are many instances when being quite close isn't close enough.

Scientists in particular have to very accurate when they measure. The more precise a measurement needs to be the more important it is that the measuring tools are calibrated to small units of measurement. It would not be good enough for a rocket scientist to give approximate measures of distance for lunar landing crafts, or for a surgeon to cut fairly close to the heart; they need to be accurate to the millimetre.

Very accurate forms of measurement are relatively new. The idea of measuring and comparing goes way back in the history of mathematics. I am looking at a picture that was brought from Egypt. It shows a Pharaoh watching his attendants weight containers. Measuring things figures prominently in paintings and carvings that were made in Ancient Egypt.

The earliest measurements were based on very portable tools - body parts! A main measurement 5,000 years ago for the Egyptians was the cubit. This was the length from fingertip to elbow. The Greeks used a different measure - the finger, while the Romans used the foot. A foot was based on the average size of a Roman man's foot. The same measurement is used still in many countries and today is a standard 12 inches. Do you think the average size of a man's foot is still the same today? The foot is broken into twelve smaller units, inches. Medieval Britain saw the introduction of the inch, which was as long as five barleycorns. This turned out to be about the same length as the top joint of a man's thumb. That was a convenient discovery, because it was so much easier to measure with the top of a thumb that with five barleycorns!