Diet Cola and Mentos

Sir Broderick George Richter

Archduke Dylan Christopher Moore

The Reverend Kevin Patrick Connelly

IB Physics II

Chris Murray

Janurary 25, 2012

Introduction

Method

Results

Conclusion

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Introduction

Before we developed our hypothesis and method, we each brought a large amount of background information to the experiment. We had all seen many YouTube videos featuring the famous Diet Coke and Mentos experiment and knew its basic parameters. Further research yielded the following background information.

First, we learned that the massive buildup of pressure occurs when carbonation causes bubbles to accumulate on the surface of the Mentos. These bubbles rapidly expand and are forced out of the small opening of the bottle, creating a geyser. Second, we learned that the aspartame in diet cola lowers the surface tension of the liquid, making it specifically more conducive to creating a large plume. Based on this information, we began to wonder how different amounts of cola would react to the same number of Mentos and if the velocity of the plume had any relation to the height.

Our independent variable was the amount of soda in the bottle. Our dependent variables were height and velocity of plume. Our constants were the type of soda used (Big K Diet Cola) and number of Mentos used (10). We used the equation V=D/T to find the average velocity of the plume, in which D is the height of the plume and T is the amount of time it took to reach its maximum height.

Hypothesis: If the amount of soda in the bottle decreases, then the height of the plume and velocity of the liquid will also decrease because there will less liquid with which the Mentos can react.

Method

We conducted our experiment at the Byrom basketball courts, an open area with a wall in the background for scaling and measurement purposes. We set each bottle of soda a foot from the wall to prevent it from interfering with the plume. We set up the camera at the edge of a marked wall-ball court where it stayed for the duration of the experiment. For each trial, we placed 10 Mentos into a length of PVC piping and held a plastic card to the end to keep them in.  after counting down, we then unscrewed the cap of each bottle as quickly as possible. We would then cover the opening with the PVC piping and slide out the plastic card, causing the Mentos to fall into the bottle. The Mentos and cola then reacted, which was captured on camera. At one point during the experiment, the sun set and we had to use car headlights to illuminate the court. We took the footage we acquired from the trials and put them into Logger Pro, using the height of the court as a reference. We measured the height of the plume from the top of the bottle as well as the average velocity on its’ way up. We ran 3 trials at 6 different volumes for a total of 18 videos. We then charted and graphed the heights and velocities from each of these into three separate graphs.

Materials List:

• 20 Diet Cola bottles

• 14 Mentos rolls

• PVC pipe

• Card

• Video Camera

• Logger Pro

• Volume measurement device

•  Meter stick

Calculation of velocity: Velocity = Distance/Time

As the data table and graphs show, the average peak height of plume was not when the bottle was full as we had predicted, but at 1725mL.

Uncertainties were found as follows: For volume, we used a measuring device that had intervals of 50mL, giving us an uncertainty of +/- 25mL. For height, our uncertainty was human error in Logger Pro, so it was not exact. We estimated +/- 3cm. For time, our video in Logger Pro had a time of 0.2 seconds between each slide, making our uncertainty +/- 0.1.

Conclusion

We have concluded that there is an optimal amount of soda to maximize the height of the foam explosion. It peaked at the second highest amount of soda, and we were surprised with the outcome. Our hypothesis was not supported, because there is an amount of soda between full and empty that creates a bigger plume. When we discovered the full soda did not achieve the same height as the trials with slightly less we were shocked. We had assumed that the more liquid there was the more aspartame and carbonation there would be to react. We could not explain this phenomenon but we theorize that the extra space in the bottle allowed more bubbles to form prior to the explosion, therefore providing a higher plume because the bubbles are more easily propelled than the liquid. However, there are many sources of error that could have altered our data. When the sodas were opened some of the reacting gases may have left the bottle at varying speeds, and there were inconsistencies in pouring out the soda as we attempted to do it quickly. Also, the mechanism we used to drop the Mentos was not perfectly efficient, resulting in Mentos that were not all dropped at the same time or speed. And finally some human errors such as shaky video and not exact measurements in Logger Pro. We could have improved the experiment by performing more trials for each amount of soda and by being more careful when following the steps of the method.

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