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S1E2abcd
The Water in Weather
Teacher Background Information
This section is included for your own background knowledge
and is not intended for direct student instruction.
S1E2 a, b, c, d:
The focus of this standard is to build the students’ experiences with the water cycle. They
need to understand the water cycle’s relationship to weather by making observations
about changes in water from one state to another, and changes in the weather over time.
The three most familiar states of matter are solid, liquid, and gas. A distinctive feature of
a gas is its ability to expand, filling the volume of any container. Liquids, like gases,
have no fixed shape, but have a fixed volume that they can occupy. Solids have a moreor-less fixed shape.
Matter can change from one of state to another - such as a solid ice cube melting into
liquid water and liquid water changing into steam as it is boiled. As matter goes through
these changes, it cannot be created nor destroyed (conservation of matter), therefore, the
weight of an ice cube would be the same as the weight of the resulting liquid water after
it melts. Likewise, water from an open container does not “disappear”, but exists as
invisible water vapor that escapes into the air over time. In a closed container, the water
vapor is trapped and will eventually condense back into liquid water.
Water continually circulates between the Earth’s surface, the air, and underground,
changing form but never increasing or decreasing in overall volume. This circulation of
water is driven by the sun’s heat energy. As the sun heats bodies of water such as the
oceans, lakes, and rivers, the liquid water evaporates as gaseous water vapor into the air.
This water vapor then rises, cools, and condenses into clouds. From these clouds the
water will fall back to the Earth as liquid or solid precipitation, collecting in streams and
rivers that eventually empty into the oceans.
Liquid raindrops form in warm clouds as millions of cloud droplets coalesce and join
together as they fall to the Earth. In cold clouds, cloud droplets coalesce to form ice
crystals as well as water droplets. The type of precipitation that reaches the ground in
this case depends on the temperature of the air through which the crystals fall. If the air
is chilly all the way down, the crystals will fall as snowflakes, a solid form of
precipitation. Sleet, also a solid, is formed when the crystals fall through a layer of warm
air and melt, then re-freeze as they enter a layer of colder air. Liquid rain results if the
ice crystals fall through a layer of warmer air and melt. Hailstones, another solid form of
precipitation, are formed when the ice crystals are carried up and down by strong air
currents in thunderclouds. During this turbulent ride in the thunderclouds, moisture
accumulates in frozen layers around the ice crystals.
Grade 1 – The Water in Weather
9
Unit Background