Physical Quantities and Measurement Techniques PDF

PHYSICAL QUANTITIES AND MEASUREMENT TECHNIQUES HOW TO MEASURE QUANTITIES ACCURATELY WHERE TO POSITION YOUR EYE View the scale wrongly introduces what we call a parallax error. The reading obtain will be inaccurate by a small...

PHYSICAL QUANTITIES AND MEASUREMENT TECHNIQUES HOW TO MEASURE QUANTITIES ACCURATELY WHERE TO POSITION YOUR EYE View the scale wrongly introduces what we call a parallax error. The reading obtain will be inaccurate by a small amount. To reduce this error and improve the accuracy of the reading, the scale should be viewed DIRECTLY IN LINE with it. Examples Length using a ruler Micromete r screw Gauge Measuring cylinder Must be on the flat surface. Bend down to the meniscus to take the reading level with the meniscus Repeated readings 1. Take repeated results of the same measurement. 2. Calculate the AVERAGE from all the results. 3. The results are presented in a table. Example measuring the diameter or mass of an object. MEASURING LENGTH Rulers can be used to measure small distances of a few centimetres (cm). They are able to measure to the nearest millimetre (mm) A ruler can measure small distances to the nearest mm The length of the pencil is …………………………. LARGER DISTANCES When measuring larger distances (of a few metres) a tape measure is more appropriate or, when measuring even larger distances, a trundle wheel MEASURING VOLUME Measuring cylinders can be used to measure the volume of liquids By measuring the change in volume, a measuring cylinder can also be used to find the volume of an irregular shape Measuring Time Stop-clocks and stopwatches can be used to measure time intervals An important factor when measuring time intervals is human reaction time. This can have a significant impact upon measurements when the measurements involved are very short (less than a second) Worked example A stopwatch is used to measure the time taken for a runner to complete a lap of a 400 m track. The images below give the readings on the stopwatch at the start and the end of the lap. Calculate how long it took the runner to complete the lap. Give your answer in seconds. Multiple Readings Suppose you have to measure the thickness of a sheet of paper The thing that you are trying to measure is so small that it would be very difficult to get an accurate answer If, however, you measure the thickness of 100 sheets of paper you can do so much more accurately Dividing your answer by 100 will then give an accurate figure for the thickness of one sheet This process of taking a reading of a large number of values and then dividing by the number, is a good way of getting accurate values for small figures. EXAMPLES