1
learning resource guide
backyard bergs
An iceberg is a floating piece of freshwater ice that has broken off the seaward end of a glacier or
polar ice sheet. The separation of icebergs from glaciers mostly occurs during spring and summer
in Greenland and Antarctica.
Only about 11 percent of an iceberg is visible above the water’s surface because ice is only slightly
less dense than water. The ice only just floats; the larger part of the ice sinks beneath the surface.
Make your own backyard bergs to test how much ice floats above the water and how much
hides underneath.
What you need:
• balloon
•
plastic bag (zip-lock bags work well)
•
rubber band
•
large bowl, bucket or fish tank
•
tray of ice-cubes
•
ruler
•
calculator
This activity involves making two icebergs: one in a
balloon, and one in a plastic bag. You could make lots
of other different shaped icebergs using a variety of
balloons, bags and containers.
1. F
ill the balloon with water until it is about the size of
a grapefruit.
2. Tie off the end of the balloon and place it in the freezer.
3. Repeat steps 1 and 2 using the plastic bag, except this
time, seal the top using the rubber band. Be careful
not to overfill the bag.
4. Wait for 12 to 24 hours to fully freeze your icebergs.
5. Fill the bowl, bucket or fish tank with cool water.
6. Add the tray of ice-cubes and stir until they have melted.
7. Take your icebergs from the freezer and remove the
balloon or bag.
8. Place the icebergs on the sink and measure the height
of each one.
9. Place the icebergs in the bowl, bucket or fish tank and
measure how much of your iceberg is floating above
the water.
Put your results into this easy calculation:
HEIGHT ABOVE WATER
TOTAL HEIGHT
= PART A
PART A x 100 = % OF ICE ABOVE THE WATER
The answer should fall somewhere between 11 percent
(1/9 of the height) and about 12.5 per cent (1/8 of the
height).
(Note: This simplified activity only uses height, and not volume, to demonstrate that usually more of an iceberg is underwater than above water.)
Most icebergs look white because they are full of tiny
bubbles that reflect all wavelengths of visible light in equal
amounts.
Icebergs can also be blue, green, brown or black. In blue
icebergs, the ice is compressed so much that the air
bubbles are pushed out. Without air bubbles, blue light is
reflected and the other wavelengths of light are absorbed.
Sometimes crevasses in the parent glacier fill up with
meltwater that refreezes too quickly for bubbles to form,
making the icebergs look blue and white striped.
The unusual and vivid green of some icebergs is a result of
algae growing in the ice. These green icebergs have rolled
over, exposing sections that were previously underwater.
Brown or black icebergs are just dirty. Dust, rocks and
dirt can accumulate in the glacier as it travels over the
land. When an iceberg breaks off the glacier, it can have
dirt layers deep within the ice giving it a brown or black
appearance.
2
learning resource guide
dancing ice
What makes ice float? And how can you make it dance?
Try this activity to find out and learn about buoyancy.
What you need:
• a tall glass or plastic container
•
•
some vegetable oil
ice (try adding some food coloring to make it
easier to see)
1. Fill the glass with oil.
2. Drop a block of ice into the glass. The ice should float
in the middle of the oil.
3. Watch the ice as it melts.
You will find drops form on the ice, then fall slowly through
the oil. As the drops form and fall, the ice will rock from
side to side and move up and down.
This activity i s all about density. The density of a material
is how much a given volume of that material weighs. For
example, one cubic meter of liquid water weighs 1000 kg,
so it has a density of 1000 kg/m³.
When you drop an object into a liquid, it feels the forces of:
•
gravity, which pulls it down
•
buoyancy, which pushes it up.
When you drop something into a liquid, it displaces some
of the liquid (pushes it out of the way). An object placed
in a liquid feels an upward force equal to the weight of the
liquid it is displacing. This force is called buoyancy.
GRAVITY
BUOYANCY
Photography © Vanessa Berlowitz
An object floats if its weight is less than the weight of the
liquid it’s displacing. The object will sink if it weighs more.
In other words, an object will float if it’s less dense than
the liquid it’s displacing, but it will sink if it is denser. This is
even true for liquids. Liquid water is denser than oil, so the
oil floats on the water.
Water is weird stuff! One of the ways water is strange is
that it is less dense as a solid than as a liquid.
Ice and vegetable oil have almost the same density, around
920 kg/m³, so a block of ice dropped into oil will barely
move. As the water melts, it turns into denser, liquid water,
which tends to stick to the ice before it drops off. If there is
enough liquid water on the ice, then the density of the ice
and water together is greater than the oil, so they will sink.
Once the drop of water falls off the ice, the ice floats up
again.
It’s a good thing that ice floats on water. In winter, some
rivers and lakes freeze on the surface. If ice was denser
than water, then the rivers and lakes would freeze from the
bottom up, which would kill plants growing in them and
starve most of the fish and other marine life.
3
learning resource guide
poles apart
Try this activity to see how melting ice and snow affect
sea levels.
What you need:
• film canister filled with soil,
with the lid on
•
two clear plastic glasses
•
water
•
two ice cubes
•
a marker pen
1. Place the film canister upside
down into one cup. This
represents an island.
2. Fill each glass half-way
with water.
3. Place one ice cube on top
of the ‘island’ and the other
ice cube in the water in the
second glass. Mark the level
of the water on each glass.
4. Once both ice cubes have
melted, see whether the
water level has risen.
Photography © Yva Momatiuk & John Eastcott/
Minden Pictures/Getty
The ice cube floating in the water
has already shifted, or displaced,
the water in the glass; so when
it melts, the level will barely rise.
But the ice cube on the land (film
canister) will not displace the
water until it melts and drips into
it, making the water level rise.
Only the melting of land-based
ice and snow (like Antarctica)
will increase the sea level. The
melting of floating ice (like the
North Pole) will not affect the
sea level much.
4
learning resource guide
deep freeze
How do you make super-cool water? You can try putting it in the freezer but you’ll probably find the
water will very quickly turn into ice.
Ever wonder why this happens, and how oceans don’t freeze solid when it’s below 0 ºC? Find out
how by cooling water down without freezing it.
What you need:
• freezer
•
spoon
•
water
•
salt
•
ice
•
two plastic glasses
•
marker pen
•
empty tin
ACTIVITY A:
1. Fill two plastic cups with the same amount of water.
2. Add four big spoonfuls of salt to one cup and mark the
outside of the cup with ‘S’.
3. Place both cups in the freezer (make sure they’re
balanced and won’t fall over!).
4. Check the cups every hour for four hours. Then leave
them overnight and check the next morning. What’s
the different between the two cups?
Water normally freezes (changes from a liquid to a solid) at
around 0 ºC. However, adding salt to the water lowers the
temperature at which water freezes. In other words, water
can be colder than 0 ºC and still not actually be frozen.
Salty water does eventually freeze but the water has to be
a lot colder than ordinary water.
The first activity proves this. The cup with plain water in it
should freeze solid in about four hours, but the cup with
the water and salt may not freeze solid at all. Instead,
some bits of ice will form but they can only do this by
getting rid of the salt. Eventually, you are left with solid
ice and some very salty water at the bottom of the cup.
When this happens in the ocean around Antarctica, the
very salty water sinks to the bottom of the ocean and is
called Antarctic Bottom Water.
In the second activity, adding salt to the can of ice and
water lowers the temperature of the water to below 0 ºC.
When water vapor (tiny bits of water in the air) in the air
touches the cold sides of the metal, the water vapor freezes
into a thin layer of ice or frost on the outside of the can.
ACTIVITY B:
1. Fill the tin can about three-quarters full of ice. Then fill
the tin can with just enough water to cover the ice.
2. Dry the outside of the can with a paper towel.
3. Sprinkle four big spoonfuls of salt over the top of the
ice and give it a quick stir with the spoon.
4. Watch what happens to the outside of the can over the
next ten minutes. Try adding more ice and salt.
Photography © Vanessa Berlowitz
5
learning resource guide
slicing ice
Can you think of a way to cut right through a big chunk of ice without breaking it? It is possible,
and we’ll show you how!
What you need:
• large ice block (freeze some water in a plastic bowl)
•
length of flexible wire
•
two heavy weights
•
narrow board
•
somewhere to perform the activity - a bathtub or large
sink is ideal.
1. Place the ice block on a narrow board across the
bathtub.
2. Attach a weight to each end of the wire.
3. Lay the wire across the top of the ice, with the two
weights hanging down on either side.
4. Take a look every 30 minutes or so.
The weight on the wire causes the ice to melt, just where
the wire touches the ice. The wire will gradually cut
through the ice, but the ice will re-freeze above it. After
a while your wire will be embedded well inside the block
of ice. Eventually it will cut all the way down through the
block - and yet the block will still be whole.
You can see this in action with ice-skates. All of your
weight rests on the two thin steel blades of the skates.
This great pressure causes the ice directly under the blade
to melt. So the blade slips easily across the ice on a very
thin layer of water. As soon as the skate moves away, the
surrounding ice freezes that water again. If you tried to use
ice-skates on a concrete skating rink, you wouldn’t get
anywhere at all.
Glaciers are massive rivers of ice that move slowly along in
the bed they have carved over thousands of years. Some
of the world’s largest glaciers are in Antarctica. When
Antarctic glacial ice finally reaches the sea, it breaks off to
form huge icebergs.
Glaciers move between 15 and 200 meters each year.
There are many different physical effects working on a
glacier to make it form and then flow downhill. One force
is the sheer weight of all the ice. This weight creates
tremendous pressure at the bottom of the glacier. The
wettest part of a glacier is at the bottom, and the slight
melting effect helps the glacier to slide along.
Pressure on ice lowers its melting point. So pressing on a
particular area of ice will make only that part melt, and only
briefly. Then the surrounding temperature of the ice will
cause the melted ice to freeze again.
15 meters
200 meters
6
learning resource guide
notes
sources
http://www.csiro.au/Portals/Education/Kids/Read-it/Polar-eyes/Antarctica-activities/backyard-bergs-activity.aspx
http://www.csiro.au/en/Portals/Education/Kids/Read-it/Polar-eyes/Antarctica-activities/dancing-ice-activity.aspx
http://www.csiro.au/en/Portals/Education/Kids/Read-it/Polar-eyes/Antarctica-activities/poles-apart-activity.aspx
http://www.csiro.au/en/Portals/Education/Kids/Read-it/Polar-eyes/Antarctica-activities/deep-freeze-activity.aspx
http://www.csiro.au/en/Portals/Education/Kids/Read-it/Polar-eyes/Antarctica-activities/slicing-ice-activity.aspx