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Dimensions and units
We usually consider quantities like mass,length, time, and
perhaps charge andtemperature, as fundamental dimensions.
We then express the dimensions of otherquantities like speed,
which is length/time,in terms of the basic set.
Every quantity which is not explicitlydimensionless, like a pure
number, has
characteristic dimensions which are notaffected by the way we
measure it.
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Dimensions and units (cont)
Units give the magnitude of somedimension relative to an
arbitrary standard.
For example, when we say that a person issix feet tall, we mean
that person is six timesas long as an object whose length is
definedto be one foot.
In contrast to dimensions, of which only afew are needed, there
is a multitude ofunits for measuring most quantities.
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Dimensions and units (cont)
Dimensionless quantities should be easier,in that they do not
have units at all, but insome ways they are more complicated.Some
examples: Ratios, Angles,Pressure,
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Graphing To be useful, the results of a scientific
investigation or technical project must becommunicated to others
in the form of an oralpresentation, technical report, journal
article ormonograph.
Effective communication often requires figures,such as
photographs, drawings, or graphs, inaddition to words and
equations.
When choosing the type of figure to use, startwith the type of
data you have collected orintend to collect, and the type of
information thatyou intend to convey.
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Reporting data in text or tables
Assuming that you have a normaldistribution, a set of data for a
singlesample can be written in text or in a tableas mean error,
which is usually eitherthe standard deviation or the
standarddeviation of the mean (e.g., 9.8 0.02 m/s2).
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Random Error
Random error, known also as experimentalerror, contributes
uncertainty to anyexperiment or observation that
involvesmeasurements.
One must take such error into account whenmaking critical
decisions.
When you present data that are based on
uncertain quantities, people who see yourresults should have the
opportunity to takerandom error into account when decidingwhether
or not to agree with your conclusions.
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Random Error (cont)
Without an estimate of error, theimplication is that the data
are perfect.
Random error plays such an important rolein decision making, it
is necessary torepresent such error appropriately in text,tables,
and in figures.
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Random Error (cont)
To represent random error, wecommonly use what we call an
errorbar, consisting of a vertical line thatextends from the mean
value inproportion to the magnitude of the error.
The most common type of error bar that
you will encounter includes a "cap" thatclearly indicates the
end of the bar in eachdirection.
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References
Introductory Laboratory Courses inBiochemistry & Cell
Biology,syllabushttp://www.ruf.rice.edu/~bioslabs/bios211/index.htm
Abdisalam Issa-Salwe lecture notes,Taibah University.
