BACKGROUND:
Sand has been used to describe many human qualities. A vagabond has been
referred to as "driftless like ...sand". Endless time is
"sand that drifts forever". We are all but a "grain of sand
on the beach." Children can spend hours on the beach, creating sand
castles, or digging to reach the other end of the world. Sand can cover you
up, but not make you dirty...it is clean to play with. Children look at sand
falling through an hour glass fascinated by every grain that falls and some
paint with different color sands to create works of art. Sand is loved so
much by children that adults have created sand boxes, so their children can
play with it.
It's funny to think that sand can be associated with two very opposite
climatic conditions. First, water moves sand at beaches by the ocean and in
lakes or rivers. Second, in hot, dry areas like Death Valley and the Sahara
Desert, the wind shifts sand. If you understand the process that creates
sand, you can see that in both situations some kind of erosion of the
surrounding rock is creating the sand, but different processes move it
around.
Sand is the Earth in miniature. Every rock eventually succumbs to erosion
and will become sand with time. Mighty mountains are slowly chipped away by
natural forces like wind and rain. Over long periods of time, the mountains
will become sand.
There are many different sizes of sand. Particles of sand are cemented
together to become sedimentary rocks, which may have different appearances,
depending on the size and composition of the sand particles.
PROCEDURE:
- Tell students that some sand grains are heavier than others. Ask
students which particles would "settle out" first - the heavy,
big pieces of sand or the small, lighter pieces of sand. Hopefully, they
will agree that the heavy pieces will settle first.
- Tell students that they are going to make a similar
"falling" sand machine." Have the students put about 3-5
tablespoons of the sand mixture from the module in a jar. (Note: the
shorter the jar the less mixture you should put in). Fill the jars three
quarters full of water. Have them put the top on securely and then shake
the mixture. Have them watch the mixture as it settles.
- Ask the students to describe what they have seen. After a few of their
stories draw the following picture on the board, emphasizing that the
heavy particles settled first and the lighter ones settled last. You can
reuse the mixture, even if wet. If you are storing the mixture, dry it
well.
