Here is something for those who paid attention in high school physics class. See the diagram below.
This is a metal (wood, plastic, glass) tube. The end on the left is closed, while the end on the right is open. If you blow across the open end sound waves travel back and forth within the tube. The lowest frequency at which the air column in the tube vibrates is call the fundamental frequency of the tube. In this case the fundamental frequency is 420 Hz.
The tube below is the same length as the tube above, but the left end is open. Again when you blow across the open end on the right you get the air column vibrating.
What is the fundamental frequency of the open tube? Why? Hint: wind musical instruments operate off this principle.
Post your responses in the comments section below.