Section 1-2 Measurement

Measurement Measurement – a comparison between an unknown quantity and a standard Ex: if you measure the mass of a rolling cart the unknown quantity is the mass of the cart and the standard is the gram In order to measure something you must have a standard

Comparing Results When comparing measurements, even if the numbers aren’t exact they can still support each other if they fall within the uncertainty of the other measurements If the results including uncertainties overlap, then the answers are in agreement

Precision Versus Accuracy Both are characteristics of measured values. Precision – the degree of exactness of a measurement The finer the divisions on the scale used to measure the more precise the measurement will be Ex: Figure 1-10 on page 12 Accuracy – describes how well the results of a measurement agree with the “real” value The most accurate measurement is the measurement closest to the “real” value Instruments are calibrated to ensure accuracy

Techniques of Good measurement Instruments have to be read at the right angle If a spring balance is not read from directly above the measure, if it is read at an angle you will get a different, less accurate value This shift is caused by Parallax – an apparent shift in the position of an object when viewed from different angles

GPS The GPS system offers a good example of accurate and precise measurement There are 24 satellites orbiting the earth sending signals 4 satellites are used for each location measurement to ensure accuracy Accuracy depends on the receiver, for your car it may be within a few meters, for geophysicists they can detect millimeters of movement