The atmosphere is mainly composed of
the gases oxygen, nitrogen, and carbon dioxide. Air molecules are
constantly in motion, bumping into each other with a certain force. When
air is heated, the molecules move faster and hit each other with a
greater force, hence the air expands. The weight that the air exerts is
called atmospheric pressure. Atmospheric pressure decreases the higher
you go up in elevation. This is why some people might feel more tired at
the top of the mountain than at sea level. Oxygen is less abundant the
further you go from the surface of the Earth.
- You may want to go over the LAB
materials to make sure students observed this motion of fluid. Many
students will want to play with the materials and may prevent going into
detail on each of the items. Use this post lab to complete the material.
If you have completed the lab we suggest that you demonstrate other
"fun" examples of fluids in motion. The case of the
"dieting egg" can illustrate how pressure not only moves
objects, but can actually force objects through an opening.
- You may want to do this experiment
with your students and then challenge them to repeat it. Remind students
to do this experiment with an adult present.
- You will need a peeled boiled egg,
a bottle with an opening just large enough to prevent the egg from
falling through, a small piece of paper and a match. Set fire to a small
piece of paper. Place the paper into the bottle and quickly place the
egg on top of the bottle. The egg will plop into the bottle!
- The fire heated the air inside the
bottle causing the air to expand and with some of the air molecules
escaping from the top. With less air in the bottle (decreased pressure)
than the outside (greater pressure) the egg is pushed into the bottle.
Students cannot see the motion of the air, but it is occurring.