Physical Quantities and Measurement

Study Notes

A physical quantity is a characteristic of an object or phenomenon that can be measured
Examples: length, mass, time, temperature, electric current
Physical quantities can be classified into two categories:
- Fundamental quantities: cannot be expressed in terms of other quantities (e.g. length, mass, time)
- Derived quantities: can be expressed in terms of fundamental quantities (e.g. speed, force, energy)

Measurement: the process of assigning a numerical value to a physical quantity
Measurement involves comparison with a standard unit
Units:
- SI units (International System of Units): standardized units used globally
- Non-SI units: units that are not part of the SI system (e.g. inches, pounds)
Measurement instruments:
- Direct measurement: measuring a quantity directly using an instrument (e.g. ruler, thermometer)
- Indirect measurement: measuring a quantity indirectly by measuring other related quantities (e.g. measuring speed by measuring distance and time)

Direct measurement: measuring a quantity directly using an instrument
Indirect measurement: measuring a quantity indirectly by measuring other related quantities
Fundamental measurement: measuring a fundamental quantity (e.g. length, mass, time)
Derived measurement: measuring a derived quantity (e.g. speed, force, energy)

Systematic error: error that occurs due to a flaw in the measurement instrument or technique
Random error: error that occurs due to chance or unpredictable factors
Uncertainty: the range of values within which the true value of a measurement is likely to lie
Precision: the closeness of repeated measurements to each other
Accuracy: the closeness of a measurement to the true value

A physical quantity is a characteristic of an object or phenomenon that can be measured, such as length, mass, time, temperature, and electric current.
Physical quantities can be classified into two categories: fundamental quantities and derived quantities.
Fundamental quantities cannot be expressed in terms of other quantities, whereas derived quantities can be expressed in terms of fundamental quantities.

Measurement is the process of assigning a numerical value to a physical quantity, which involves comparison with a standard unit.
Standard units used globally are called SI units (International System of Units), while units that are not part of the SI system are called non-SI units.
Measurement instruments can be used for direct measurement, which involves measuring a quantity directly, or indirect measurement, which involves measuring a quantity indirectly by measuring other related quantities.

Direct measurement involves measuring a quantity directly using an instrument.
Indirect measurement involves measuring a quantity indirectly by measuring other related quantities.
Fundamental measurement involves measuring a fundamental quantity, such as length, mass, or time.
Derived measurement involves measuring a derived quantity, such as speed, force, or energy.

Systematic error occurs due to a flaw in the measurement instrument or technique.
Random error occurs due to chance or unpredictable factors.
Uncertainty is the range of values within which the true value of a measurement is likely to lie.
Precision refers to the closeness of repeated measurements to each other.
Accuracy refers to the closeness of a measurement to the true value.