1. Section 1-2
Measurement

2. 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

3. 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

4. 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

5. 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

6. 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