Measurement of Length
While the S.I. unit for length is the metre (m), there is a large range of lengths – from subatomic particles measuring mere femtometers (10-15 meters) to astronomical distances spanning billions of light-years. In physics, precise measurements of length are essential for understanding the fundamental principles that govern our universe.
The following items are used to measure lengths of different ranges:
| Instrument | Typical Range | Precision | Examples of Uses |
| Measuring Tape | zero to 10 metres | 1 mm | Width of a room |
| Metre Rule | zero to 1 m | 1 mm | Length of string for a pendulum |
| Digital Calipers | zero to 15 cm | 0.01 mm (can be recorded to 0.1 mm) | External and internal diameters of a beaker, depth of a hole |
| Digital Micrometer Screw Gauge | zero to 3 cm | 0.001 mm (can be recorded to 0.01 mm) | Diameter of a ball bearing or wire |
The following video shows how digital calipers are used.
How to use the digital micrometer
Measurement of Time
In the physics laboratory, time measurements are typically carried out using a digital stopwatch. Although this device can provide time values accurate to 1/100th of a second, the recorded time measurements are generally rounded to one decimal place in seconds. This practice is influenced by the inherent limitations of human reaction time.
One of the common measurements made is the period of oscillation of a simple pendulum, which the time it takes for one complete back-and-forth motion, from one side (e.g., the rightmost point) to the other side (e.g., the leftmost point) and back again. For example, the period of oscillation for the pendulum in the animation below is 2.8 s.
Using a stopwatch such as the one in your mobile phone, measure the time it takes for one complete oscillation in the simulation of a simple pendulum below. Vary the length of the pendulum by adjusting the position of the blue dot and observe how the period changes.
In order to improve the precision of measurement using a digital stopwatch for a pendulum, rather than timing just one swing, time multiple swings (e.g. 10 or more) and calculate the average time. This reduces the impact of reaction time and other human errors.
Additionally, try to start and stop the stopwatch as the pendulum crosses the centre position instead of the turning points, where the uncertainty of start and stop time is higher.
For even greater precision, consider using a photogate and a datalogger. Photogates are devices that can automatically record the time when an object, such as a pendulum bob, passes through a light beam. This eliminates the need for manual timing and can provide very accurate measurements.