Physical Quantities and Measurement

Study Notes

Measurement involves a number and a unit to describe a physical quantity.
Units are universally accepted and used to communicate scientific information without ambiguities.

Concept of length: distance between two points.
Units of length:
- Metre (m)
- Submultiples: centimetre (cm), millimetre (mm)
- Multiples: kilometre (km)
Devices for measuring length:
- Metre ruler
- Measuring tape
Measurement with a ruler:
- Readings can be affected by parallax error
- Correct reading is obtained when the eye is in front of and in line with the reading

Concept of mass: quantity of matter contained in a body.
Unit of mass:
- Kilogram (kg)
- Submultiples: gram (g), milligram (mg)
- Multiples: quintal, metric tonne
Devices for measuring mass:
- Beam balance
- Electronic balance
Measurement with a beam balance:
- Standard weights are used
- The total of standard weights gives the mass of the given body

Concept of temperature: degree of hotness or coldness of a body.
Unit of temperature:
- Celsius (°C)
Devices for measuring temperature:
- Clinical thermometer
- Laboratory thermometer

Symbols for units are written in small letters.
Units are never written in plural.
A space is left between the numerical value and the unit.
Negative powers are used to express compound units.### Electronic Balance
The structure of an electronic balance is the load-bearing part that transfers the load of an object to the load cell.
The load cell converts the load force into electrical signals.
The signal conditioner is the electronic part that processes the electrical signal and displays the mass.

Time is the interval between two instances or events.
A solar day is the time taken by the Earth to complete one rotation about its own axis.
The mean of 365 solar days in a year is called the mean solar day.

The S.I. unit of time is the second (s), which is defined as 1/86400 part of a mean solar day.
One second is the time between two consecutive ticks of a pendulum wall clock.
A minute (min) is a bigger unit of time, with 60 seconds making 1 minute.
An hour (h) is a still bigger unit of time, with 60 minutes making 1 hour.
A day is the time taken by the Earth to rotate once on its own axis, which is equal to 24 hours.
A year is the time taken by the Earth to complete one revolution around the Sun, which is equal to 365 days.

A pendulum clock measures time by the time taken for a pendulum to complete one oscillation (2 seconds).
The clock has a circular dial with 12 markings divided into four quadrants, with 60 small divisions.
The second's arm moves one small division every second, the minute's arm moves one small division every minute, and the hour's arm moves 5 divisions every hour.