Unit 1 – Introduction to Physics
QUANTITIES AND UNITS
VOCABULARY
Physical quantities
mass
force
 Current
unit
SI units
 International system
kilogram second
 Basic quantities
meter
ampere
 Derived quantities
Kelvin
mole
 Candela
scale
periods
 Avogadro’s number
triple point
 Absolute temperature scale
black body

QUANTITIES AND UNITS
Physical quantities are things such as mass,
force, and current, which can be quantified by
measurement.
 All physical quantities have to be measured in
some way and each therefore has its own unit.
 Units are chosen by international agreement
and are called SI units abbreviated from the
French (Systeme International d’Unite).

QUANTITIES AND UNITS
All quantities are classified as either basic
quantities or derived quantities.
 Basic quantities are a set of quantities from
which all other quantities can be defined.
 Each basic quantity has its basic SI unit, in
terms of which any other SI can be defined.

Insert basic quantity table
QUANTITIES AND UNITS
Basic SI Units
 Kilogram (kg) is the SI unit of mass. It is equal
to the mass of a platinum iridium cylinder kept
at Sevres, near Paris.


Second (s) is the SI unit of time. It is equal to
the period of a type of radiation emitted by the
cesium-133 atom.
QUANTITIES AND UNITS

Meter (m) is the SI unit of length. It is equal to
the distance light travels in a vacuum in
1/299,792,458 of a second.

Ampere (A) is the SI unit of electric current. It
is equal to the size of a current flowing through
wires in a vacuum, that produces a force of 2 X
10-7 N every meter.
QUANTITIES AND UNITS

Kelvin (K) is the SI unit of temperature. It is
equal to 1/273.16 of the temperature of the
triple point of water on the absolute
temperature scale.

Mole (mol) is the SI unit of the quantity of a
substance. It is equal to the amount of
substance which contains 6.023 X 1023
particles. (Avogadro’s number)
QUANTITIES AND UNITS
Candela (cd) is the SI unit of intensity of light.
It is equal to the strength of light from
1/600,000 m2 of a black body at the
temperature of freezing platinum and at a
pressure of 101,325 N/m2.
 A black body is a hypothetical object which
absorbs all radiation that falls on it, and is also
the best radiator (heat energy emitter).

QUANTITIES AND UNITS
Prefixes
 A given SI unit may sometimes be too large or
small for convenience.

 Example:
The meter is too large for measuring the
thickness of a piece of paper.
QUANTITIES AND UNITS
Prefixes
 Standard fractions and multiples of the SI units
are therefore used and written by placing a
prefix before the unit.

 Example:
1 millimeter (mm) is equal to 1/1000 of a
meter.
 Thickness of a sheet of paper is 0.1 mm which
equals .0001 m or 1/10,000 of a meter .
Insert Fractions and multiples table
QUANTITIES AND UNITS
Derived quantities are quantities other than
basic quantities.
 Derived quantities have derived SI units which
are defined in terms of the basic SI units or
other derived units.
 They are determined from the defining
equation for the quantity and are sometimes
given special names.

Insert derived quantity table