Analysis and Discussion
After a photograph of the reaction is taken, it is immediately recorded in a data table, and scrutinized with Adobe Photoshop® to see if the image revealed any change in the volume of the balloon at the instance the photo was taken. The desirable photograph will not show any signs of an explosion, which is why it was important to compare the photograph of the reaction with the pre-shot to look for changes in the size of the subject. If the balloon showed no signs of sign reduction, then the appropriate delay interval in the computer would be increased so that the shutter of the camera would open later in the reaction. If the balloon showed signs of expansion or of explosion, a decrease in the delay interval would follow.
If it is suspected that the photograph of the subject during the reaction
is smaller, then an overlay function in Adobe Photoshop® is used to see
the difference between the two photographs. To do this, the reaction picture
is inserted over the pre-shot in a new layer. The ring stand holding the balloon
apparatus is aligned exactly, and we subtract the image of the reaction from
the pre-shot using the difference function in the software. This function
darkens all parts of the overlaid photographs that are the same, showing the
volume difference of the balloons as the only bright area of the photo
Here is one of three groups of pictures where the subject actually did shrink:
We were also able to analyze other photographs that did not show signs of shrinking. One such picture is of an expanding balloon with three color flashes on it. With this picture we are able to calculate how much fast the balloon expanded. The photo is shown here:
Knowing that the diameter of the stopper on which the balloon is secured is 2.5cm, we can calculate the initial diameter of the balloon to be 13.8cm and the final diameter of the balloon to be 28.6cm in diameter. the flashes in this image were set off .799 milliseconds apart and two flash intervals had elapsed before the balloon reached it's final diameter. This accounts for a time interval of 1.598 milliseconds. We can now calculate the average speed of the change in diameter.
Avg. Speed=Change in diameter/Change in time=(.286m-.138m)/(.001598sec)
Avg. Speed=92 meters/sec or roughly 200 miles per hour!
Notice, however, that the calculation is an average speed over the course of the entire image. If you look at the photograph though, you can see that the balloon expands much more from the yellow to the green image, to the green and the red. This reveals a substantial decrease in the expansion speed of the reaction.
Rotating Mirror Analysis
The rotating mirror was a useful tool in giving us a reference in space as well as a reference in time. Using our rotating mirror images we can tell how fast the reaction progresses with respect to time. One such image is again shown below.
Notice that the space from right to left is passing time, so distance measurements must be made vertically. Using the same method as in the first calculation above we can determine dimensions based on the scale of the balloon's stopper. Now we can once again measure the average speed of the reaction.
Avg. speed=change in diameter/change in time=(.24m-.117m)/.00246sec
Avg. speed=50 meters per second or roughly 100 miles per hour!
Notice again that the balloon is not expanding at a uniform speed. As time passes (from right to left), the speed of the expanding balloon is slower. This concurs with the speed decrease in the still photograph above.
Each of our progressive setups yielded photos that gave us a better insight into the behavior of combusting hydrogen and oxygen. Our still photos captured the balloon at key instances in the reaction. This lead to our finding that at least part of the time, the hydrogen and oxygen combustion results in the the reactants or products (or some combination of both) occupying less volume. Our rotating mirror photographs gave us a better perception of the behavior of the reaction over a span of time, which revealed the non-uniform expansion speed.
All photos on this site are copyrighted by Brian Sweeney
and Tim Collier, 2002.
To inquire about picture use please contact Loren Winters at winters@ncssm.edu