Physics Topic 1 Physical Quantities, Units and Measurements (part 1)

 Syllabus Content 

• 1.1 Scalars and Vectors 
• 1.2 Measurement techniques 
• 1.3 Units and symbols

1.1 Physical Quantities and Units

• Physics is the study that deals with matter and energy and their interactions.
• Major branches of physics are general physics, thermal physics, waves, electricity, magnetism, and atomic physics
• Any measurable  characteristic of something is called physical quantity 
• Some of the commonly used physical quantities are mass, time, force, speed, distance, electric current, pressure, volume, temperature.

                                                                     Fig. 1.1

• A physical quantity always needs a magnitude (i.e. a numerical value and a unit) in order to specify it. Fig. 1.1
• There are two types of Physical quantities

1. base quantities 
2. derived quantities 

• Base quantities are the physical quantities in terms of which other physical quantities can be described. Mass, time and distance are some examples of base quantities.
• Derived quantities are the physical quantities which can be described in terms of base quantities. Force, Velocity, and acceleration are some examples of derived quantities. 
• A unit is a standard of measuring a physical quantity correctly.
• There are two types of Units: 

1. base units
2. derived units        

• Base Units are units for base quantities e.g. second (s), meter (m), kilogram (k), etc.
• Derived Units are the units for derived quantities e.g. newton (N), watt (W), meter per second (m/s) etc.
• A set of base and derived units is called system of units.
• British Engineering System and System International Units (SI units) are two examples of system of units. 
• System International units (SI units) have been adopted internationally for the efficient measurement of physical quantities.

                        

Fig. 1.2

• Fig. 1.2 shows a list of seven base quantities and their corresponding SI units.

  Derivation of Derived Units.

                                                                            

                                                                          Fig. 1.3

• Derived units are expressed in terms of base units by means of mathematical symbols of multiplication and division.
• The fig. 1.3 shows how some of the derived units are derived from base units.

Prefixes 

• Prefixes are the terms used internationally for the multiples and sub multiples of various units. For example, 2500g can be better written as 2.5 kg and 0.008 m can be written as 8mm.
• A list of commonly used prefixes are given in fig. 1.4.