Introduction
In Weather: Air, you helped your students learn that air is a material
"thing" with properties that are typical of all matter, but
are not as readily recognized for air as for some other things; specifically,
having mass and taking up space. Air is all around us. It takes up space
(fills a balloon or a cup), it exerts pressure (holds sheets of newspaper
on a table top), and has inertia which can be seen as it moves or resists
moving from place to place (resists being fanned with cardboard sheets).
Although it is invisible to our eyes, our other senses readily detect
its presence all around us. Later, your students will learn that measuring
the properties of air forms the basis of measuring the atmospheric conditions
that we call "weather".
In these investigations, students make observations and measurements
of additional properties of air that combine to produce weather conditions.
These observations are made at levels appropriate to the students' levels
of understanding and skills. This will form the building blocks they will
need to understand the molecular nature of atmospheric gases and the kinetics
of molecular movement, which are concepts they will develop at later stages
of their learning about the natural world.
One property of air that can be measure is its temperature. Air temperature
is measured with thermometers. Common thermometers consist of a liquid-in-glass
tube attached to a scale.
The scale can be marked (graduated) in degrees Celsius (°C) or degrees
Fahrenheit (°F) or both. The tube contains a liquid that is supplied from
a reservoir or "bulb" at the base of the thermometer. The internal
liquid is usually mercury or red-colored alcohol. In the interest of safety,
alcohol thermometers are mainly used in schools, since mercury is very
toxic.
Alcohol thermometers work due to the expansion and contraction of liquid
relative to temperature. As the liquid in the bulb of the thermometer
is heated, it expands and rises up in the tube. Conversely, as the liquid
in the bulb is cooled, the liquid contracts and falls in the tube.
In this investigation, your students will develop the concept of expanding
liquids on which a liquid-filled thermometer is based, and then apply
this knowledge by using an outdoor thermometer to record daily temperatures.
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