The air in a tube open at both ends is sent into its fundamental resonance. One end of the tube is then closed and the air column is again set into its fundamental resonance. The resonant frequency after the end is closed.

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask

hi there!

out of the two, (b) precision would be more reasonable.   however, both a and b could be pretty reasonable.

-awesomerepublic   : )

a skateboard rolling across the street - apex