Measurements in physics
Fundamental Concepts in Measurements
- Physics is fundamentally a science of measurement which seeks to quantify the properties of the world around us.
- Working with measurements often requires an understanding of the SI units (International System of Units).
- Base units are the simplest building blocks of measurement. These include the second (s) for time, the metre (m) for length, the kilogram (kg) for mass, the Ampere (A) for electric current, the Kelvin (K) for temperature, the mole (mol) for amount of substance, and the candela (cd) for intensity of light.
- Derived units are complex units formed by combining base units, such as the Newton (N) for force or the Watt (W) for power.
Accuracy and Precision
- Accuracy refers to how close a measurement is to the true value of the measure.
- Precision however, is about how consistently you can get that result.
- Be wary of the parallax error that occurs when the measured quantity and the marking of the measuring device are not in the same line of sight.
- The zero error is another common error, occurring when the measuring instrument does not start measuring from exactly zero.
Uncertainty in Measurements
- Random uncertainties arise from unpredictable statistical fluctuations in the measured data.
- A systematic uncertainty is one that remains constant across all measurements.
- Absolute uncertainty is expressed in the same units as the original measurement.
- Percentage uncertainty is the absolute uncertainty divided by the measured value, multiplied by 100%.
- Uncertainty can be reduced by using better quality equipment, performing more trials, and controlling the experiment conditions more carefully.
Significant Figures and Scientific Notation
- Significant figures are digits in a number that carry meaning contributing to its precision.
- We adjust our measurements to contain an appropriate number of significant figures based on the precision of the measuring device.
- Scientific notation is a way of writing numbers that accommodates values too large or small to be conveniently written in decimal form.
- When writing numbers in scientific notation, one digit is placed to the left of the decimal point, and the decimal place is then moved to create a number between 1 and 10. This number is multiplied by ten raised to an exponent.
Data Presentation
- To present data effectively, you can use tables, graphs, or diagrams.
- Tables should be well-organised with columns and rows labelled appropriately.
- When drawing graphs, label the x and y-axes with the quantity being measured and its unit. The independent variable typically goes on the x-axis.
- Diagrams and plots should be neat and clearly annotated for effective communication.