Numbers And Units Worksheet With Answer Key
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8W4 NUMBERS AND UNITS
SI Base Units
In almost all cases, reporting numerical results requires that the units are specified. If sports
reporters announce a new world record of “9.79 s for the 100 m sprint”, we know exactly what
they are talking about. Similarly, a TV cook specifies that 25 g of butter is needed for a recipe –
merely stating that “25 of butter is required” can lead to obvious ambiguity.
*
The preferred units in science are the SI
base units, shown in Table W4-1 below. Other units
are derived from these seven units.
Table W4-1 SI Base Units
Physical Quantity
Name of Unit
Symbol
Mass
kilogram
kg
Length
metre
m
Time
second
s
Temperature
kelvin
K
Amount of substance
mole
mol
Electric current
ampere
A
Luminous intensity
candela
cd
Derived and Compound Units
Units for other quantities are derived from these seven units. To do this, take the equation used
to define the quantity and substitute the appropriate SI base unit.
Example
The volume (V) of cube is given by the length (l) of a side cubed:
l
3
V = l
As the SI unit of length is the metre, the SI unit of volume is the
3
cubic metre or m
.
l
l
An extremely important derived unit is that for energy. There are many equations that relate
2
quantities to energy changes. (eg Einstein's famous E = mc
) In every case, the SI unit for
2
–2
energy is the joule (symbol J = kg m
s
).
If there is not a common derived unit, the unit may be made of two units.
W4-1
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The International System of Units (abbreviated SI from the French Le Système International d'Unités)
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