Game Development Reference
In-Depth Information
Quantity
Notation
SI unit
Other units
Length
L
m
cm, km, in, ft, mi, light year, furlong
Time
T
s
min, hr, ms
Mass
M
kg
g, slug, lb (pound-mass)
Velocity
L/T
m/s
ft/s, m/hr, km/hr
L/T
2
m/s
2
ft/s
2
, (m/hr)/s, (km/hr)/s
Acceleration
ML/T
2
Force
N (Newton)
= kg m/s
2
lb (pound-force), poundal
L
2
m
2
mm
2
, cm
2
, km
2
, in
2
, ft
2
, mi
2
,
acre, hectare
Area
L
3
m
3
mm
3
, cm
3
, L (liter), in
3
, ft
3
, teaspoon,
fl oz (fluid ounce), cup, pint, quart, gallon
Volume
psi (lbs/in
2
), millibar, inch of mercury,
atm (atmosphere)
Pressure
Force/Area
= (ML/T
2
)/L
2
= M/(LT
2
)
Pa (Pascal)
= N/m
2
= kg/(m s
2
)
Energy
Force × Length
= (ML/T
2
) L
= ML
2
/T
2
J (Joule)
= N m
2
=
kW hr (kilowatt-hour), foot-pound, erg,
calorie, BTU (British thermal unit),
ton of TNT
kgm
s
2
m
kgm
2
s
2
=
Power
Energy / Time
= (ML
2
/T
2
)/T
= ML
2
/T
3
W (Watt)
= J/s
=
hp (horsepower)
kgm
2
s
2
s
−1
kgm
2
s
3
=
1/T = T
−1
Hz = 1/s = s
−1
= “per second”
Frequency
KHz = 1, 000 Hz, MHz = 1, 000, 000 Hz,
“per minute”, “per annum”
Table 11.1
Selected physical quantities and common units of measurements
a given duration of time. So we can write frequency in generic units as 1/T
or T
−1
, which you can read as “per unit time.” One of the most impor-
tant measurements of frequency is the Hertz, abbreviated Hz, which means
“per second.” When you express a frequency in Hz, you are describing the
number of events, oscillations, heartbeats, video frames, or whatever per
second. By definition, 1 Hz = 1 s
−1
.
Table 11.1 summarizes several quantities that are measured in physics,
their relation to the fundamental quantities, and some common units used
to measure them.
Of course, any real measurement doesn't make sense without attaching
specific units to it. One way to make sure that your calculations always
make sense is to carry around the units at all times and treat them like
algebraic variables. For example, if you are computing a pressure and your
answer comes out with the units m/s, you know you have done something
wrong; pressure has units of force per unit area, or ML/(T
2
L
2
). On the
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