# Misconceptions - Measurements

 Measurement is only linear. Double the dimensions of an object and they think the csa and volume also double - they find the fact that csa increases by a factor of 4 and volume (and therefore the mass) by a factor of 8 surprising. Any quantity can be measured as accurately as you want. .... all you have to do is use a modern 'digital' instrument - they think 'old' instruments are out of date and useless. They find the accuracy of precision instuments being related to construction difficult to understand - it needs to be 'new' and 'electronic' to be any good in their eyes! Children who have used measuring devices at home already know how to measure with them. You can't teach an old dog new tricks - if they have done it at home - or been show it at primary school they do not listen when you go through how to use it! Imperial measurements are inaccurate ....all down to 'old' is inaccurate way of thinking! You can measure to any proportion of the smallest unit shown on the measuring device. They think they can estimate a third or quarter of a scale division - put them right on this! You should start at the end of the measuring device when measuring distance. Zero errors due to 'bashed' metre rulers always give a problem - so do ones that are constructed with a 'gap' to allow for wear and tear! Some objects cannot be measured because of their size or inaccessibility. They think a n object must be "touched" to measure it. Use of trig to measure the height of a tree is sometimes suspect! Mass is a quantity that you get by weighing an object. In general speak they are interchangable - to a pupil so are their units and numerical values! The five senses are infallible. Optical illusions are good on this one! There is only one way to measure perimeter. .... and that is 'all of the way' round - mathematical calculation is suspect! Only the area of rectangular shapes can be measured in square units. The idea of measuring a circle in square units give some children problems Surface area can be found only for two-dimensional objects. Surface area is a concept used only in mathematics classes! Practical making of wrapping for an object helps with this - it is limited to rectangular shapes, but it helps - they have done 'nets' in maths. You cannot measure the volume of some objects because they do not have "regular" lengths, widths, or heights. They need to think of volume as an occupied 'space' rather than a mathematical construct - displacement can experiments are fun! The density of two samples of the same substance with different volumes or shapes cannot be the same. Density is a concept difficulty for many... practical hands on experience is vital.