Fanta-stic Decay

Purpose: to demonstrate that the bubbles made by pouring a fresh bottle of Fanta or Coke pop randomly and thus the foam head decays exponentially

Materials: bottle of Fanta, Coca-Cola, or other soda, funnel, graduated cylinder, stopwatch or clock, scientific calculator (if available)

Procedure: Each lab group needs at least five students: one to pour the soda, two observers, one timer, and one to record data.

1.     Set up the graduated cylinder with a funnel over it as shown. 2.     Pour soda in slowly until the top of the foam reaches the top volume mark. 3.     The timer calls �Go!� every 5 sec. At each call from the timer, the observers read and report the volume at the top of the foam and at the bottom of the foam. 4.     The recorder writes down the time and volumes every 5 sec. 5.     Steps 3 and 4 continue until the foam is just about all gone. 6.     Students should find the volume of the foam for each time entered by subtracting the bottom volume from the top volume. They should then calculate V/VO , where VO  is the first recorded volume of the foam. 7.     If there is a scientific calculator, students may also calculate the natural logarithm of the volume fraction, ln (V/VO ). Lab set-up for the soda decay experiment.

 

With the data recorded, students should graph V/V_O  as a function of time. They should attempt to verify that the curve is similar to exponential decay and try to calculate the half-life from the curve by finding the time at which the value of V/V_O  is equal to 0.5 . If they are able, they should also graph ln (V/V_O ) as a function of time. If the decay is a true exponential, this graph should be a straight line with a negative slope. The half-life is then ln 2 divided by the magnitude of that slope.

Done properly, this lab shows exponential decay similar to that seen with radioactive isotopes and for a similar reason. Bubbles in the foam pop randomly just as particles decay randomly.

Fanta-stic Decay Student Worksheet

Data Table:

Time (sec) Top Volume (mL) Bottom Volume (mL) Net Volume (mL) V/VO ln (V/VO) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Graphs:

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