Physics is the study of the natural world and how physical objects behave. It began in ancient Greece when early scientists called "physikoi" tried to understand the natural world using observations and experiments. Today, physics involves measuring various quantities accurately using standardized metric units like meters, kilograms, and seconds. Measurements in physics consist of a number and a unit, and the International System of Units (SI) precisely defines the fundamental base units and derived units used in physics.

1. What is physics?
Physics is a way of describing the physical
world
• 6th Century B.C. in the Greek city of
Miletus (now in Turkey) a group of men
called “physikoi” tried to answer questions
about the natural world. Physics comes
from the Greek word φύσης “physis”
meaning “nature”, and the Latin word
“physica” meaning natural things.

2. Investigations in physics generally follow
the scientific method

3. Units in Physics
Some old measuring units

4. • Physics experiments involve the
measurement of a variety of
quantities.
• These measurements should be
accurate.
• The first step in ensuring accuracy is
defining the units in which the
measurements are made.

5. The Nature of Measurement
A Measurement is a quantitative
observation consisting of TWO parts
Part 1 – number
Part 2 - scale (unit)
Examples:
20 grams
6.63 x 10-34 Joules

6. The Fundamental SI Units
(le Système International, SI)
Physical Quantity (symbol) Name Abbreviation
m
Kg
S
A
K
Mol
cd

7. SI Definitions
meter:
The meter is the length of the path
travelled by light in vacuum during a time
interval of 1/299 792 458 of a second.
Historical International
Prototype Metre bar, made
of an alloy of platinum and
iridium, that was the
standard from 1889 to
1960, then this was
replaced by the above-mentioned
definition.

8. SI Definitions
kilogram:
The kilogram is
the unit of mass; it is
equal to the mass of
the international
prototype of the
kilogram. This is made
of platinum-iridium & it
is kept at the BIPM, in
France.
Photograph @ BIPM
“Visit the page”

9. SI Definitions
second:
The unit of time, it was defined
originally as “the fraction 1/86 400 of the
mean solar day”.
In 1967 it was replaced by the following
definition :
The second is the duration of
9 192 631 770 periods of the radiation
corresponding to the transition between the
two hyperfine levels of the ground state of
the cesium 133 atom.

10. SI Definitions
ampere:
The ampere is that constant current
which, if maintained in two straight parallel
conductors of infinite length, of negligible
circular cross-section, and placed 1 meter
apart in vacuum, would produce between
these conductors a force equal to 2 x 10-7
newton per meter of length.

11. SI Definitions
candela:
The candela is the luminous
intensity, in a given direction, of
a source that emits
monochromatic radiation of
frequency 540 x 1012 hertz and
that has a radiant intensity in
that direction of 1/683 watt per
steradian
(http://en.wikipedia.org/wiki/Steradian)

12. SI Definitions
kelvin:
The kelvin, unit of thermodynamic
temperature, is the fraction 1/273.16 of
the thermodynamic temperature of the
triple point of water.
mole:
The mole is the amount of substance
of a system which contains as many
elementary entities as there are atoms in
0.012 kilogram of carbon 12.

13. Derived units
Derived units are combinations of fundamental
units.
Examples:
speed (v) = distance/time
units: m/s
acceleration (a) = velocity / time
units: m/s/s = m/s2
force (F) = mass x acceleration
units: kgm/s2 = N (Newton)
energy (E) = force x distance
units: kgm2/s2 = Nm = J (Joule)
charge (Q) = current x time
units: As = C (Coulomb)

14. SI Derived Units

15. SI Prefixes
Common to Chemistry
Prefix Unit Abbr. Exponent
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro  10-6

16. Metric Conversions
g
m
103 102 101 L 10-1 10-2 10-3
kilo hecto deka deci centi milli
Base
unit
Conversions in the metric system are
merely a matter of moving a decimal point.
The “base unit” means the you have a
quantity (grams, meters, Liters, etc without
a prefix.

17. Metric Conversions
g
m
103 102 101 L 10-1 10-2 10-3
kilo hecto deka deci centi milli
Base
unit
18 L
1 2 3
18 liters = 18 000 milliliters
Example #1: Convert 18 liters to milliliters

18. Metric Conversions
g
m
103 102 101 L 10-1 10-2 10-3
kilo hecto deka deci centi milli
Base
unit
3 2 1
450 mg = 0.450 g 450 mg
Example #2: Convert 450 milligrams to grams

19. Metric Conversions
g
m
103 102 101 L 10-1 10-2 10-3
kilo hecto deka deci centi milli
Base
unit
20 kg
1 2 3 4 5 6
20 kg = 20 000 000 mg
Example #3: Convert 20 kilograms to milligrams