I am interested in anti-gravity and levitation. I decided to
experiment with balloons and lifting. I have a small mouse I
wanted to float in the air and wanted to see if I could accurately
calculate the minimum amount of gas and balloons needed to lift the
mouse.
Hypothesis:
Through research and analytical calculations I can accurately predict the minimum amount of gas needed to "float my mouse".
Analytical vs. Empirical methods
I learned that analytical means to rely on equations and calculations rather than trial and error, while empirical
means to obtain a solution by observation or experiment. In this
project it would have been easy to use the empirical method. I
could just have taken my mouse to the store and started adding balloons
to it until it floated. However, I wanted to see if I could
calculate the number in advance. I then used empirical methods to
prove or disprove my hypothesis.
Methods:
Research & learn about gases and lifting
Study periodic table chart to pick gas for lifting
Research and calculate lifting power of gas
Measure weight of object to be lifted
Calculate amount of gas needed to provide lift
Determine weight of balloons and string and add to weight to be
lifted
Determine amount of gas in balloons
Predict number of balloons required
Test lift power one balloon to validate prediction
Attach balloons and lift mouse
Resolve differences between analytical prediction and empirical results
Research & learn about gases and lifting
When a balloon is held by a string, the balloon is floating in a pool
of air. The balloon displaces an amount of air. As long as
the balloon is lighter than the air it displaces the balloon well float
in air. If other objects are attached to the balloon, the balloon
must displace enough air to compensate for the weight of those objects
as well. When the balloon rises it has positive buoyancy. When
the balloon floats in mid air, without moving up or down, it is
neutrally buoyant. I wanted to calculate the minimum amount of
gas used, so my balloon should be just barely positively buoyant.
Study periodic table chart to pick gas for lifting
I studied the periodic chart and learned that it goes from the
lightest element to the heaviest. I found out that Hydrogen
was the lightest element and thought it was a good gas to use. I
later learned that Hydrogen was explosive so I did not use
it. I then looked at the second lightest element and that
was Helium. I used Helium because it was the second lightest
element and is one of the relatively inert Noble gases (which means it
doest easily combine with anything else or explode) It is available at grocery and party stores.
Research and calculate lifting power of gas
I looked at the periodic chart and found the atomic weight and
the atomic radius I was unable to calculate the lifting ability of
Helium from these facts. From a web page at Elmhurst collage I
found that that Helium has a density about 0.18 grams per liter.
Air has a density of 1.28 grams per liter. I subtracted
those and determined that Helium would have a lifting ability of about
1.10 grams per liter. I also found out that Nitrogen weighs
1.2506 grams per liter and makes up 80 % of the air we
breath. That is why the density in air is so close to the density
of Nitrogen.
Measure weight of object to be lifted I used a "triple beam balance" to determine the weight of my
mouse (10 grams). I also weighed an empty balloon and string (9
grams).
Calculate amount of gas needed to provide lift I calculated that 10 liters of Helium would lift 11 grams (1.10 grams/liter of lift x 10 liters = 11 grams).
It should require about 0.9 liters of Helium for every gram to be lifted (11 grams / 10 liters = 0.9090 liters/gram)
I should need about 9 liters of Helium to float my mouse
Determine weight of balloons and string and add to weight to be
lifted The material of the balloons and the string or ribbon also have
weight and must be considered too. I weighed an empty balloon and
string and found that they weighed 9 grams.
Determine amount of gas balloon could hold.
I had planned on calculating this, but since the balloons were an
irregular shape, I could not calculate it and had to use an empirical
method for this. I filled one of the balloons with water from a
measuring cup and found that it held 10 liters. I originally
wanted to use round balloons, because I had a formula to calculate how
much gas they would hold, based on their diameter. However, I
discovered that regular balloons are porous and would lose their Helium
too quickly. Instead I had to use Mylar balloons, which were not
available in a shape that made it possible for me to calculate the
amount of gas they could hold.
Predict number of balloons required
Based on the above calculations and empirical observations, I
calculated that three balloons and the mouse would weigh 37
grams. Since each balloon holds ten liters, three balloons would
only lift 33 grams. Therefore three balloons would not lift the
mouse. Four balloons would be required.
Test lift power one balloon to validate prediction
I then weighed the mouse once more and then attached one balloon.
The attachment of the balloon reduced the mouses weight by about 2.5
grams, which further supported my calculation of four balloons.
Attach balloons and lift mouse
I then began attaching balloons to test my analytical prediction.
I was very surprised to find that the mouse began to float after
attaching only three balloons.
Resolve differences between analytical prediction and empirical results
Looking back at the process, I think that perhaps the method of filling
the balloon with water to determine how much they could hold might not
have been accurate enough. Perhaps the balloons held slightly
more than 10 liters.
Also, I was dependent on the information from Elmhurst
college as to how much lift to expect from a liter of
Helium. It is possible their figure was slightly in error.
Lastly, the air temperature and pressure in the room may also have
contributed. If the temperature were lower, the Helium would have
contracted and the balloons would have had less lift. Perhaps the
Elmhurst figures were based on a lower temperature.
Conclusions:
My hypothesis was incorrect. I was not able to accurately predict
the amount of Helium required. I needed more information,
such as the lift of Helium at various temperatures and the exact
capacity of the balloons.