Mass is the quantity
of matter in a body. More specifically, it is the measurement of
the inertia or sluggishness that a body, in the absence of friction, exhibits
in response to any effort made to start it, stop it, or change in any way
from its original state of motion. Two items that have the same dimensions
could have different masses, and two different sized objects could have
similar mass. Mass does not change, no matter if you are in space
or on Earth. Mass is a measure of the matter within a body.
Mass is measured in kilograms and grams (metric) and slugs (English).
Weight is the force of gravitational
attraction on a body as observed on the rotating Earth or similar situation.
Weight on Earth and weight on the Moon of the same object, is different.
The English system is measured in ounces and pounds and the metric is measured
in newtons and dynes.
Although the difference between
mass and weight is real, on Earth mass and weight are very similar.
Many books do not distinguish the difference. This activity introduces
the two words, mass and weight, and acknowledges they are somehow different.
This helps students in future labs.
Volume is the quantity of space
a body occupies measured in liters and milliliters in the metric system
and ounces and pounds in the English system. The same volume of two
different substances, may have different weight and mass.
Students in the third grade just have
to understand that weight and mass are similar but not the same.
Mathematical formulas can be used to distinguish the two easier, but not
until a later grade!
- Go over the
difference between volume, mass, and weight. Emphasize that on Earth
the two measurements are similar, but in space the differences are very
important. For instance you will weigh much less on the Moon than
on Earth, but your mass is still the same. Gravity influences
weigh, so the larger the body like Jupiter, the more you will weigh.
It is not important if children remember this, as much as you begin their
understanding of the difference.
- If you have different
scales and balances you should demonstrate mass, volume and weight.
A balance measures mass. A bath scale measures weight. Liter boxes
or graduated cylinders measure volume. Go over this several times.
It is not easy to understand, but very important in later labs. Have
the students measure different things on the balance so they become familiar
with using the balance.
- You may want to use the worksheet
and have students identify which of the instruments are used to measure
volume, weight, and mass. The graduated cylinder measures volume,
the rest of the scales (spring, balance, and scale) are used to measure
weight and mass depending on the type of scale used.