First Post (Straw)

Experiment Materials Needed:
Straw
Water
Cup

Question:
Why doesn't the water in the straw "drop" when the straw is held in the air if I cover one of the opening of the straw?

Answer:
Air pressure is the main concept behind this. As air is a matter, it experiences gravity as well. Since gravity is strongest near the earth's surface, it holds the atmosphere which contains different types of air and is closest to the earth's surface. This pushing force of the air is called air pressure.

This experiment is to explore air pressure. As you hold your finger on the opening of the straw, the air in the straw could not escape. Air pressure is when air presses down on the Earth's surface. Therefore, when you hold one of the opening of the straw, the water would not drop down as it is "protected" from the weight of air, not experiencing air pressure. However, when you release the finger, there would be air pressure, pushing down the water into the cup.

Reflections/Learning Point:
Air pressure happens because air, which has mass, experiences the pull of gravity. This experiment clearly explains this to me through visually. It is a very good experiment to show air presssure in the simplest form. Another experiment to show air pressure would be the "killer straw" experiment. I feel that this experiment is very interesting and this experiment was done by me when I was an adolescent. I did this experiment unknowingly as I was playing with my straw and water then. I did not expect this to be able to enlighten me in the concept air pressure. I really like this kind of "learning from "life" experiments" style of learning!

Source: http://www.newton.dep.anl.gov/askasci/chem99/chem99313.htm