(Kelly of the Clue Crew gives the clue from a lab.)  Stretch a balloon over a glass, secure with rubber bands, then place a straw on top & you have a simple version of this device that measures air pressure
Blowing causes the air pressure between the balloons to decrease creating a... [DOC] [TLE] December 162014.pdf - Morris School District [PAR] Jan 26, 2015 ...