Introduction to the Metric System:
Mass
Mass:
Strictly speaking mass measures how much matter (atoms and
molecules) an object contains. In the context of health care you
can approximate mass as being the same as weight – that is it
measures how heavy something is.
Units (from smallest to largest):
microgram (microgram or microg), milligram (mg), gram (g),
kilogram (kg).
Common uses:
The amount of medication is often stated as a mass.
For example, 30 mg of codeine phosphate per tablet.
This means that there is exactly 30 mg of codeine phosphate in a
single tablet. (It does not mean that the tablet weighs 30 mg).
Points to consider:
•
You will commonly use weights of grams (g) and kilograms
(kg) in day to day activities such as shopping for groceries.
You therefore have an understanding of how ‘heavy’ these
masses feel relative to each another.
•
Very small masses such as micrograms (microgram or
microg) and milligrams (mg) are not detectable unless you
are using very sensitive measuring equipment. They are
not commonly used on a day to day basis.
•
Medications are dispensed to patients in very small
quantities and therefore need to be measured using very
small units such as microgram and mg.
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Representing microgram, mg, g and kg
Consider a single lead weight with a mass of 1 microgram as
shown below (the lead weight on the left hand side). In real life this
lead weight would be very, very tiny since 1 microgram is so small
but for the purpose of our explanation we can use a lead weight to
represent 1 microgram. If you were to place 1000 of these 1
microgram lead weights on top of one another you would have the
equivalent mass of 1 milligram (mg):
1000 microgram = 1 mg
1 microgram = 0.001 mg
In the same manner if you had a lead weight with a mass of 1
milligram (mg) (represented by the lead weight on the left hand
side of the image below) and you placed 1000 of these 1 mg lead
weights on top of one another you would have the equivalent mass
of 1 gram (g):
1000 mg = 1 g
1 mg = 0.001 g
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And if you had a lead weight with a mass of 1 gram (g)
(represented by the lead weight on the left hand side of the image
below) and you placed 1000 of these 1 g lead weights on top of
one another you would have the equivalent mass of 1 kilogram
(kg):
1000 g = 1 kg
1 g = 0.001 kg
© Copyright IntelliLearn Pty Ltd 2012. All rights reserved