P1- measurements and their errors

SI units

The international system of units (SI) is founded on the seven base quantities. It was created in order to establish an internationally agreed set of quantity measurement standards.

Base quantity Unit Symbol
Mass Kilogram Kg
Length Meter M
Time Second S
Quantity of matter Mole Mol
Temperature Kelvin K
Electric current Ampere A


SI prefixes

Each prefix can go before any SI unit.

T tera x1012
G giga x109
M mega x106
K kilo x103
C Centi x10-2
M milli x10-3
µ micro x10-6
n nano x10-9
p pico x10-12


Limitations of physical measurements

Types of errors:

Measurement error: The margin of error when taking measurements.

Anomalies: A result which does not fit the trend/pattern.

Zero error: Error when taking measurements that don’t start from zero e.g. scales.

Random error: An uncontrollable error.

Systematic error: A continuous error that keeps occurring.


Accuracy- how close to the true value it is

Precision- values with very little spread about the mean values

Repeatability- can the experiment be repeated with the same method and equipment and still obtain the same value.

Reproducibility- can the investigation be repeated by another person using different equipment and get the same results.

Calculating uncertainties

Resolution- the smallest quantity that can be measured with the equipment.