Rock 'n Ice
Purpose:
This activity explains why rocks are often found in ice. Members
of the North Magnetic Pole expedition team will encounter rocks in ice
quite often in their journey.
What you will need:
1 clear plastic bucket
water
1 black rock
a lot of sunshine
cold weather (Below freezing. If it is too warm outside, a freezer
will do.)
Before you begin:
Ask an adult to help you with this activity.
Be careful when lifting the bucket. It is slippery and you could
drop it on your foot.
What to do:
1. Fill the clear plastic bucket 3/4 full with water.
Take the bucket outside (or place it in a freezer) and let the water
freeze. The freezing process may take a day or two, depending on
the temperature. If outside, make sure the bucket is in the sun and not
the shade.
Place the black rock in the middle of the bucket.
4. Wait a few days and you will begin to notice that the rock has sunken
into the ice. Check the rock's progress as it moves through the ice
in the next few days.
What is going on here?
You must wonder by now how the black stone ômeltedö its
way through the ice. The rock melted into the ice because of black
body radiation, meaning that black objects absorb and radiate all wavelengths
of radiation, including infrared radiation. This absorption causes
the rock to be warmer. The black rock had enough infrared radiation
to melt the ice and sink deep into the bucket. As an additional experiment,
freeze another bucket of ice and put a black rock and a white rock on the
ice. Then, see which one goes through the ice faster.
Have you ever seen a ring of sunken snow around a tree trunk?
The black body radiation of the trunk melted the snow. Did you know
that polar bears have black skin underneath their fur? Again, the
dark skin absorbs the sunÆs heat to help keep the polar bear warm.
Explorers use black body radiation when they choose black tents or black
pots and pans to maximize heat. Another example is black clothes.
You will be hotter in the summer if you wear black clothes. That's
why most summer clothes are made from lightly colored materials.
Activity courtesy of Jeff Ward, a member of the Arctic Exploration Team.
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