Expert: Ralph Salier-Hellendag - 1/26/2005

Question
" My daughter 8th grade is doing sci fair proj:
Wine bottle filled with solutions of vinegar and baking soda (varying proportions for her data table)cork applied, lay it on its side and wait for gas to build up, shooting cork a measurable distance in a measurable amt of time. She hypothesises that if you use a certain propotion and double it, cork will go twice as far. What equations do we use to calculate the pressure built up inside bottle? Thanks! Desperate Mom with background in bio sciences


Answer
Hi Desperate Mom,

Sounds like a great idea for a science fair project..  

It will be nearly impossible to calculate the pressure in the bottle however, you can infer the pressure by measuring the distance the cork flies.  So make sure that the base of the bottle is anchored so that it does not move and that all of the energy is used pushing out the cork.  You may want to put charcoal on the cork so that it marks the spot it hits to make it easier for you to measure.  The place it stops may not count.  The reason being is that it could bounce off of the wall or other object.  You also need to fix at least two of the variables.  I recommend that you only fill the wine bottle half full of the vinegar and vary the amount of baking soda.  Also you will need to be very carful that the cork us set in the bottle the same distance each time you test since this could impact the release of pressure.

When you lay the bottle down, remember the gas will also push out some of the vinegar in a spray and perhaps as a gush.  Make sure that it is done where it can be easily cleaned up.

To calculate the pressure build up, you will need to know the volume, speed of gas generation and the friction variable on the cork.  I'm not sure that it will be possible to calculate all of these with out instrumentation.  You would need a pressure guage and perhaps a velocity meter.