Why study water, ice, and snow? We can observe all three states – either directly or indirectly. While we know that water vapor is invisible, students can see their breath condense in cold air or fog a mirror to prove that the vapor is there. Water is an important substance – its constants are used to calculate specific gravity and calories. All our students come to school with firsthand experience, and it is easy to make real world connections.
One real world connection is found in the polar regions, since all three states are found year round in the forms of land and sea ice, the Arctic and Southern Ocean, and of course, the water vapor in the atmosphere.
Depending on where you live, you may have helped your students cut snowflakes out of paper. If so, you know that a snowflake is hexagonal, or 6-sided. This is a direct result of one of the characteristics of water molecules. As the liquid changes to solid, it forms a crystal. In its liquid state, the water molecules can attract the opposite end of the next molecule, which allows them to be closer together than they can be in their crystal form. As the crystal forms, the molecules align themselves to share the hydrogen bond (the green circles)…which develops the hexagonal shape we recognize in the snowflake. Instructions for cutting paper snowflakes: http://www.highhopes.com/snowflakes.html
Because ice is less dense than liquid water, it is able to float. This is the only substance on Earth which behaves this way. This picture of the icebergs in the lower left also illustrate the difference in density between salt and fresh water. Fresh water is less dense than salt water because of the dissolved solids in the salt water. This picture shows icebergs, which are formed from fresh water, floating in the salt water of the ocean. Ice’s ability to float is essential for life on earth, and it makes ice a useful substance for teaching about density and buoyancy.
Ice that forms on land from snow is the result of accumulations of snow that are compressed over time. Over time, the weight of the accumulated snow can cause it to be compressed to form ice. This is how glaciers are formed. On the other hand, ice that forms on a puddle, river, or lake (bodies of water on land) must form from the surface of the water itself. The water must cool to the freezing point, and then the molecules begin to line up (as described previously). Snow also accumulates on lake or sea ice, but it is subject to drifting and isn’t really part of the ice, unless it remains in place and is compressed. So ice forming on water forms on the bottom of the ice, while on land it forms on top. When ice forming on water becomes thicker, it acts as an insulating layer and keeps the water temperature from cooling further. This is why sea ice is only a few meters thick, while the ice sheets in Antarctica and Greenland are miles thick. Let’s talk about some of the locations where ice forms, both on land and on water.
There are many names for ice, depending on the amount of ice, its formation, and position. On land, a very large continent sized mass of ice made from snow is an ice sheet. Earth’s remaining ice sheets are found in Antarctica and Greenland. A smaller, but still sizeable mass of ice at the summit of a mountain or a mountain range is an ice field. An area with a large mass of ice that is moving and surrounded by ice is an ice stream. Finally, a specific area of moving ice because of a slope or its own weight is a glacier.
A glacier can only form if the snow doesn’t melt away over the summer months. Then the next season’s snowfall will accumulate on top of that layer. Over time, the snow becomes grainy and compressed. This is known as firn . After many years, the snow will be compressed enough to become a more dense solid. Even on a relatively flat surface, the compressed snow will begin to spread out under its own weight (sort of like pancake batter). Once the ice is moving, whether downslope or outward from its own weight (or both), it is called a glacier .
Glacial ice may move toward the coast and extend out onto or into the ocean, forming an ice shelf. If chunks break off, they form icebergs. It’s important to remember, though, that these are still both freshwater ice floating on or in saltwater.
Ice that forms on the ocean, however, has its own set of terms. Ice that forms from seawater is called sea ice. Because most of the salt is excluded as it is formed, it is only slightly salty and much less salty than the sea water that it formed from, except where pockets of brine may be trapped. When sea ice breaks into large floating chunks, they are known as ice floes. Sea ice forms in stages, one of which is called pancake ice (picture in upper right). Sea ice is not totally flat! Wave action moves it around, causing the formation of raised edges and pressure ridges.
Land-based ice is obviously above sea level. If the ice is lost, through melting or evaporation (actually called sublimation--directly changing from solid to gas, without going through the liquid phase), then the water will be added back into the water cycle…eventually finding its way back to the ocean. On the other hand, sea ice is already floating (displacing its mass). It was formed from sea water and floats because it is mostly freshwater ice which has expanded in forming the crystals. Melting of sea ice will not raise sea level, except possibly in certain regions, depending on the coastal features.
Both land-based ice and sea ice are found in the Arctic and Antarctica. In the Arctic, Greenland is home to an ice sheet and glaciers are found across the regions. Sea ice forms and melts seasonally, and has been in sharp decline in recent years. Antarctica is made of the East and West Antarctic Ice Sheets, which are separated by the Transantarctic Mountains. Sea ice forms around the continent each winter, doubling its size.
Ice can be used to meet many science content standards. In this presentation, we’ll focus on physical science and refer briefly to earth and space science as well.
One concept that can be taught is states and changes of matter. We promote combining hands-on investigations with content area reading to help students develop content knowledge, vocabulary, and practice reading strategies. In Water and Ice, students in grades K-2 make qualitative observations about water as it changes states. They extend their knowledge by reading 4 books: Water as a Solid, Water as a Liquid, Water as a Gas (not shown), and the Water Cycle (not shown). Students in grades 3-5 take a more quantitative approach in Heat Energy and Water, and generalize their knowledge to all solids, liquids, and gases through nonfiction reading.
While teaching states and changes of matter, you can also make polar connections by modeling and reading about glaciers, icebergs, and sea ice. In How Do Snowflakes Become Ice? Students model glacier formation with marshmallows (or snow cone ice). Do It Yourself Iceberg Science was originally designed for students in the middle school years, but the basic procedure can be used to allow students to create their own icebergs. The sea ice set is a collection of images and videos to help students visualize the ice of the polar regions. Pair these investigations with nonfiction reading: Icebergs, Ice Caps, and Glaciers for primary students and Icebergs and Glaciers by Seymour Simon for upper elementary students.
As we all know, misconceptions can impact learning, so it is important to be mindful when planning instruction. Students may believe that a change in state means a change in mass. We recommend formative assessment, such as the Uncovering Student Ideas in Science series from NSTA Press. Volume 1 includes an assessment probe called “Ice Cubes in a Bag” which will help assess student ideas about this concept.
Another possible misconception is that solids can only melt with heat. We know that solids, like ice, can melt with pressure. Two examples are at the base of glaciers and as an ice skater glides across the ice. Target this misconception with an activity that involves a discrepant event. In Blue Ice Melt, students use blue ice cubes to simulate glacial ice. They leave one as a control and push the other around on wax paper while wearing rubber fingertip pads. They observe dents forming in the top of the ice cube and conclude that since the rubber fingertips block heat transfer, the melting must be due to the pressure they place on the ice cube.
Yet another misconception is that larger volumes of water need lower temperatures to freeze (or melt). The size of the ice cube (or block) will affect how long it will take to melt, But the temperature at which ice melts or freezes is the same. The temperature may be affected by pressure, however…such as at high elevations and under the weight of large masses of ice or water or rock. Another formative assessment probe called “Freezing Ice” in volume 2 of Uncovering Student Ideas in Science helps you assess what your students think about this concept.
Density and Buoyancy are two more concepts that can be addressed with a study of ice. In grades K-2, students investigate whether objects sink or float. Including ice in a variety of sizes and shapes and allowing students to create their own icebergs will help them begin to understand that ice, no matter its size or shape, will float in water. Content area reading – a story written by our project staff (Floating Ice), Icebergs, Ice Caps, and Glaciers, and a fictional story called Lulie the Iceberg can help your students understand that ice floats. Note: Lulie the Iceberg is about an iceberg that breaks off in the Arctic and travels all the way to Antarctica to join the “ancestors” (ice sheets of Antarctica). This is clearly a fictional story! Yet the story is wonderful, with beautiful illustrations, and much of the other scientific content (currents, the climate and weather of the various latitudes) is in fact accurate. It might be a good springboard for science instruction.
Students in grades 3-5 can begin to examine ice and why it is able to float in liquid water. Two discrepant events (water molecule pockets and the magic trick with ice) will prompt students to investigate water’s unique properties – they pour rubbing alcohol into a glass of water and see that it does not overflow! The rubbing alcohol fills in the spaces left by the liquid water (described in the activity as pockets). Students also observe relative density as an ice cube floats in water but not rubbing alcohol. Content area reading is crucial to help students form correct explanations – so you can use our nonfiction stories and Seymour Simon’s icebergs and glaciers for a real world connection.
This is another misconception. Students may observe a bulging frozen can of soda or a lump on a iceberg and assume that this happens because the molecules actually grow. Use content area reading (such as our nonfiction stories) and models (gumdrops and marshmallows) to help students visualize the molecular structure of water. Students can create a model of a water molecule, then work in groups to model the hexagonal structure that forms in ice.
I’d like to take a moment to talk about our nonfiction stories for students. We feature a new story each month that coincides with the theme of our magazine. They are found in the Feature Story column of the magazine. They are available at three grade levels, and as text-only, a full-color, illustrated book, and electronic book with audio narrative.
Another misconception is that floating or sinking is based on an object’s weight, while we know that it is based on the density of an object in comparison to water (or the liquid surrounding it). Again, use formative assessment probes from the Uncovering Student Ideas in Science series to elicit student ideas and plan instruction.
You can also tie in the water cycle by including ice and snow. Many times, we focus on rain as the sole form of precipitation, but the snow and ice of the polar regions is part of the global water cycle. This is especially important to think about as our climate changes and more and more of that ice melts.
Physical Science From the Poles
Saturday, November 1, 2008 Physical Science from the Poles Jessica Fries-Gaither Elementary Resource Specialist and Project Director Ohio State University [email_address]
http://beyondpenguins.nsdl.org Today’s presentation features material related to the August 2008 issue: Water, Ice, and Snow Resource list provided at the end of the session.
Why study water, ice, and snow? <ul><li>We can observe it (directly/indirectly) in all three states </li></ul><ul><li>Specific gravity and calories are determined using water’s properties </li></ul><ul><li>Students have firsthand experience </li></ul><ul><li>Easy to make real world connections </li></ul>
Water in the polar regions: solid, liquid, and gas. Chris Linder, Woods Hole Oceanographic Institute
What can snowflakes teach us about water? http://www.classzone.com Liquid water Solid water Pidwirny, M. (2006). "Physical Properties of Water". Fundamentals of Physical Geography, 2nd Edition . Date viewed: October 16, 2008. http://www.physicalgeography.net/fundamentals/8a.html
Ice formation Ice on land is usually from precipitation, unless it is freezing water that is present in saturated soil. Ice forming on water develops at the liquid surface of the water…and therefore on the bottom of any ice layer at the surface. National Science Foundation National Science Foundation
Land-based ice <ul><li>Ice Sheet </li></ul><ul><li>Ice Field </li></ul><ul><li>Ice Stream </li></ul><ul><li>Glacier </li></ul>National Science Foundation Henning Thing Danish Polar Centre
Glaciers http://www.answers.com/glacier National Science Foundation
Land-based ice…over the ocean <ul><li>Ice shelf </li></ul><ul><li>Iceberg </li></ul>National Science Foundation National Science Foundation
Ice on/in the ocean <ul><li>Sea Ice </li></ul><ul><li>Ice Floe </li></ul>Photos courtesy of Dr. Vicky Lytle, National Science Foundation Science and Technology Center for Remote Sensing of Ice Sheets, University of Kansas; National Science Foundation
Effects on sea level: Land ice vs. sea ice National Science Foundation Jason Box Byrd Polar Research Center <ul><li>Land Ice </li></ul><ul><li>Above sea level </li></ul><ul><li>Formed from fresh water </li></ul><ul><li>Melting will raise sea level </li></ul><ul><li>Sea Ice </li></ul><ul><li>Already floating </li></ul><ul><li>Formed from sea water </li></ul><ul><li>Melting will not raise sea level </li></ul>
Ice in the Polar Regions Images not to scale U.N. Environment Programme: http://maps.grida.no/arctic/ Byrd Polar Research Center
Ice and the National Science Education Standards <ul><li>Science as Inquiry </li></ul><ul><li>Physical Science </li></ul><ul><li>- States and Changes of Matter </li></ul><ul><li>- Properties of Matter (buoyancy, density) </li></ul><ul><li>Life Science </li></ul><ul><li>- Ice as a platform for many species </li></ul><ul><li>Earth and Space Science </li></ul><ul><li>- Water Cycle </li></ul><ul><li>Science in Personal and Social Perspectives </li></ul><ul><li>- Changes in polar ice caps </li></ul>
States & Changes of Matter Water and Ice Heat Energy and Water Students in grades K-2 observe water as it changes states. Students in grades 3-5 investigate heat's effect on water. Hands-on investigations and content area reading
States & Changes of Matter How Do Snowflakes Become Ice? Model glacier formation with marshmallows. Do It Yourself Iceberg Science Create icebergs with film canisters. Sea Ice Set A collection of images and video. Polar Connections: glaciers, icebergs, sea ice
Misconception Alert! A change in state (melting, freezing) means a change in mass. Formative Assessment Probe: “ Ice Cubes in a Bag” (Vol. 1) Use formative assessment to elicit student ideas and plan instruction accordingly.
Solids can only melt with heat. Blue Ice Melt: Ice can melt with pressure . Misconception Alert! Target with an activity that involves a discrepant event. Henning Thing Danish Polar Center Kptyson Flickr
Larger volumes of water need lower temperatures to freeze. Misconception Alert! Use formative assessment to elicit student ideas and plan instruction accordingly. Formative Assessment Probe : “ Freezing Ice” (Vol. 2)
Density and Buoyancy: Grades K-2 Sink or Float? Students determine whether objects sink or float in water. Include ice in various shapes and sizes! Do It Yourself Iceberg Science Create icebergs with film canisters, watch them float.
Density and Buoyancy: Grades 3-5 Water Molecule Pockets Demonstrate liquid water’s molecular structure with a discrepant event and a model. The Magic Trick with Ice A discrepant event – an ice cube floats in water but not rubbing alcohol.
Water expands as it freezes because the molecules become larger. Misconception Alert! Use content area reading and models to help students visualize water’s molecular structure.
Nonfiction stories for students Feature Story column of the magazine Available at three grade levels (K-1, 2-3, and 4-5) Available as text, illustrated book, and electronic book
Misconception Alert! Floating or sinking is based on an object’s weight . Use formative assessment to elicit student ideas and plan instruction accordingly. Formative Assessment Probes: “ Floating Logs” & “Floating High and Low” (Vol. 2)
The global water cycle Don’t forget about ice and snow! Beyond Penguins and Polar Bears Issue 5 (August 2008): Water, Ice, and Snow The Straight Edge, Inc. http://www.straightedgeinc.com/
Beyond Penguins Web Seminar Series: November 13th--Energy and the Polar Environment http://expertvoices.nsdl.org/polar Beyond Penguins and Polar Bears August 2008, Issue 5 http://beyondpenguins.nsdl.org Beyond Penguins and Polar Bears Blog Interested in learning more? Post: Physical Science From the Poles
Jessica Fries-Gaither [email_address] Thank You! Sue Sheridan