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Lecture 01: Standards and Units, Unit Consistency and
Conversion,
Uncertainty and Significant Figures
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Objectives
At the end of this lecture, you should be able to: describe what
physical quantities are; convert quantities into different units;
recognize the importance of significant figures; express quantities
in scientific notation; justify the dimensional consistency of a
relation.
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PHYSICS
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Example:
Physical quantityPhysical quantity is any number that is used
to
describe a physical phenomenon. Units are very important!
F = 30 N
(physical quantity) (magnitude) (standard)
Time 60 secondsLength 1.0 meterMass 50 kilograms
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Fundamental unitsInternational system (SI or the metric
system)
Table 1. SI Base Units
Quantity Name of Unit SymbolLength meter mMass kilogram kgTime
second sElectric current ampere AThermodynamic temperature
kelvin KAmount of substance mole molLuminous intensity candela
cd
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Significant figures
All non-zero digits are significant Zero digit/s before or after
a decimal point is/
are significant only if preceded by non-zero digits.
If there is no decimal point, zero digit/s after the rightmost
non-zero digit is/ are not significant.
The coefficient/s of a number written on scientific notation
is/are significant.
a x10 b a = coefficient , 10 = base, b = exponent
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Significant figures
Addition and subtraction The sum or difference can contain no
more
place values than the least precise measurement.
Multiplication and division The number of SF in the final answer
is equal
to the least number of SF among the values.
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Unit consistency and conversion
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Dimensional AnalysisDimensional analysis can be used to: -
derive an equation - check if the equation is dimensionally correct
- know the units or the dimension of a physical quantity
*check/simplify the dimension of the LHS and RHS of the
equation
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Example: Dimensional Analysis
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Exercise: Dimensional Analysis
LHS: s = Length
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LHS: s = Length
LHS and RHS are consistent (unit: Length)
Seatwork: Dimensional Analysis
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