AJO. METRIC VALUES FOR PHYSICAL CONSTANTS
535
A.1O Metric Values for Physical Constants
The primary physical constants used in coastal engineering are the properties of water. The metric equivalents of these properties are given in
Table A.5. Additional physical constants which may be helpful are given
in Table A.6. Any other necessary constants can be easily converted from
their English system value using the conversion factors given in Table A.4.
A. 11 Rules of Thumb
All engineers through their experience develop a feel for what the magnitude of certain quantities should be. For example, the maximum flow
velocity through a tidal inlet is probably between 3 to 6 feet per second.
This experience, and the ability to estimate the probable order of magnitude, serves as a valuable check on the engineer’s work. For instance, if a
calculation revealed that the inlet tidal flow speed was 18 feet per second,
or a calculated wave height for average conditions was 62 feet, the engineer
would suspect an error in the analysis.
For engineers not familiar with using the metric system, a change over
can be difficult because of the loss of feel. For this reason, the coastal
engineer must be particularly careful when first starting out using the SI
system of units. One way to check metric quantities is to convert them
into the familiar English units to see if the answer is in the expected range.
However, this often would not be necessary if a few simple approximate
conversions are committed to memory. These allow the engineer to mentally
convert from SI to English units to get an approximate result which can
then be judged according to the engineer’s feel for what the value should
be. This method is particularly useful in the field, where conversion factors
may not be readily available.
As an example of an approximate conversion, most people remember
that 1 meter is a little more than 3 feet. Therefore, a 5-meter wave is
about 5 x 3 = 15 feet high. Although the error of this approximation
is about 9%, it still provides a feel for the height of a 5-meter-high wave.
Table A.7 provides similar “rules of thumb” which can be used to mentally
convert metric values to English values.
535
A.1O Metric Values for Physical Constants
The primary physical constants used in coastal engineering are the properties of water. The metric equivalents of these properties are given in
Table A.5. Additional physical constants which may be helpful are given
in Table A.6. Any other necessary constants can be easily converted from
their English system value using the conversion factors given in Table A.4.
A. 11 Rules of Thumb
All engineers through their experience develop a feel for what the magnitude of certain quantities should be. For example, the maximum flow
velocity through a tidal inlet is probably between 3 to 6 feet per second.
This experience, and the ability to estimate the probable order of magnitude, serves as a valuable check on the engineer’s work. For instance, if a
calculation revealed that the inlet tidal flow speed was 18 feet per second,
or a calculated wave height for average conditions was 62 feet, the engineer
would suspect an error in the analysis.
For engineers not familiar with using the metric system, a change over
can be difficult because of the loss of feel. For this reason, the coastal
engineer must be particularly careful when first starting out using the SI
system of units. One way to check metric quantities is to convert them
into the familiar English units to see if the answer is in the expected range.
However, this often would not be necessary if a few simple approximate
conversions are committed to memory. These allow the engineer to mentally
convert from SI to English units to get an approximate result which can
then be judged according to the engineer’s feel for what the value should
be. This method is particularly useful in the field, where conversion factors
may not be readily available.
As an example of an approximate conversion, most people remember
that 1 meter is a little more than 3 feet. Therefore, a 5-meter wave is
about 5 x 3 = 15 feet high. Although the error of this approximation
is about 9%, it still provides a feel for the height of a 5-meter-high wave.
Table A.7 provides similar “rules of thumb” which can be used to mentally
convert metric values to English values.