Volume, Capacity and Weight
Name: Linda L.
How can I explain to my 5th graders the difference
between volume, capacity and weight?
Probably one of the best ways to show the difference between volume and
weight is to get a brick and a piece of Polystyrene foam that is the same size as
the brick. The kids can determine the volume of both by measuring the
length, width, and depth of both objects. They will see they are the same,
but when they weigh them on a scale, they will see the difference in weight.
This would also be a great time to tell them about density.
Volume is a word that is intended to describe the three dimensional size
of an object or space. For something like a box, one calculates its
volume my multiplying its length by its width by its height. You know,
the old familiar V = L x W x H. For something with an irregular shape,
like an ocean -- things get much more complicated. In the end, however,
volumes are expressed in cubic units such as, cc or cubic feet or cubic
Capacity is a term that refers to a measuring vessel or a container of
known volume. We speak of a graduated cylinder as having a capacity of
100 cc or 100 mL. If one were to measure the capacity of an irregular
vessel like a vase, by filling it with water and then pouring the water
into a graduated vessel. one would have indirectly determined the volume
of the vase and thus, its capacity.
Weight is an entirely different matter, which on its face, can have
little to do with either volume or capacity. We cannot say something is
heavy just because it is big. Consider a balloon. Nor can we say
something is light just because it is small. Consider the weight of a
rock that's much smaller than the balloon, yet much heavier. Demonstrate
this by using a scale, a balloon, and a rock to show the students.
Instead of being size-related, weight is a measure of the gravitational
force between an object and the earth. If you weighed a pillow and then
squeezed it down to the smallest possible size, you would have reduced
it volume and made no appreciable change in its weight.
Weight and volume are linked by an expression called density where d = m
/ V. Dense objects have relatively small volumes for their weight. The
uncompacted and compacted pillow illustrate this. The uncompacted pillow
has a low density because it has a large volume. Likewise, the compacted
pillow has a much higher density because its volume has been reduced.
All the while, the pillow's weight is essentially the same.
I hope this is of assistance,
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Update: June 2012