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 Buoyancy Helium-Balloon Experiments and Fun with the Scientific Method c. Donald Reinhardt, March 4, 2013
 
Helium-filled balloon experiments reveal buoyancy principles, facts and provide some simple math fun– read about virtual and real buoyancy experiments.
 
Helium Balloon with and without added weight. First photo: Balloon pressed against ceiling. Second photo: Equilibrium of balloon with balanced upward and downward forces. Forces are equal and balloon seems to walk with air currents. Photo Credit: © Donald Reinhardt, 2013

Buoyancy Defined and Explained

Buoyancy is the upward force of a gas or a liquid or any fluid. This upward force lifts an object and seems to decrease its weight. Archimedes discovered buoyancy in the third century BC. History and legend record  Archimedes'  discovery as his "Eureka" moment – he discovered a new idea and a solution to a problem, therefore "Eureka". This great idea and revelation moment came it is believed when he placed himself in a tub filled to the brim with water and when he got into the tub, it obviously overflowed. This overflow situation is illustrated by photographs with corks and water displacement shown below and in the buoyancy ideas experiments more fully discussed in this buoyancy idea and experiment article. 
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Water displacement by cork inserted into a small glass filled to the brim with water. The cork displaces an amount of water equal to its volume.
Photo Credit/Copyright 2012: Donald Reinhardt
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According to the principle of buoyancy when a gas or liquid is displaced by an object, an upward force is created that is equivalent to the mass of gas or fluid displaced.
Buoyancy is a principle of physics to know, learn and do some experiments with.
Buoyancy in Gasses or Liquids – Balloon Concepts and Virtual Experiments
Remember the scientific method here: observation,hypothesis, experimentation with results and the gathering of data and, finally, conclusions.

Helium- and Air-Filled Balloon Real or Virtual Experiment 1

Take any two similar-sized balloons. Fill one balloon with air, the other with helium and tie off the end of each balloon to prevent the escape of the gas.

Observations and Experiment 1
Notice this – the helium balloon rises, tugs upward and must be held tightly or anchored to prevent it from escaping into the air.

Observation and Experiment 2

If released (a long tethering string attached to the balloon enables the retrieval of the balloon), the helium balloon ascends rapidly.

Data and Conclusions

This upward movement of the helium balloon will continue and only begins to slow as the air gets less dense (i.e. less air molecules = a thinner atmosphere). When a helium balloon is released and permitted to rise freely into the sky it appears smaller to the eye as itrises and eventually disappears from sight. Eventully, it ascends so high in the atmosphere as to become not visible.

As the balloon continues to rise, the air becomes less dense (there are fewer atmospheric gas molecules in the higher atmosphere). Since there are fewer gas molecules higher up in the air, this also means that there are less air molecules to displace as the balloon rises higher. Therefore, although we cannot see this, we know that based on the principles of physics that the balloon begins to slow and eventually stops rising. At this point, the downward forces are equal to the upward forces and the balloon neither rises nor falls. If you are interested in exploring questions and answers on buoyancy and balloons remember to check out the links at the end of this article when you are finished reading the rest of this article. 
For this discussion we will ignore the effect of air temperature on the gas inside the balloon and consider that the temperature is constant and not varying with altitude.  Therefore, if we could accurately record the balloon's altitude and velocity we could relate and correlate this to balloon volume, air density and air displacement.
For simplicity and clarity remember these points:
  1. the balloon will rise as long as the pressure or force of the air pushing upward is greater than the total mass of the helium-filled balloon.
  2. The balloon ceases to rise when it reaches a height where the upward force of buoyancy (air displacement by the balloon) is equal to the downward forces of mass x gravity (weight) and air pressure.

Air-filled Balloon and Helium-Filled Balloon Real or Virtual Experiment Comparison.

Observation and Experimental Result
Any air-filled balloon sinks in ordinary and still air.
Conclusion
An air-filled balloon displaces the surrounding air and there is a buoyant force upward, but the internal air and the mass of the balloon has a downward force that is greater than the buoyant force upward, therefore the balloon sinks.

Wind or Thermal Energy Applied to an Air-Filled Balloon.

Observation
If there is a gust of wind, the wind's kinetic energy is a force which causes the air-filled balloon to rise; when the wind subsides or stops, the balloon descends.
Hypothesis
The air-filled balloon rises because the force of the wind pushes against the balloon and overcomes the balloon's total mass and the downward force of gravity. The balloon sinks when the total and combined downward forces exerted by gravity, the mass of the physical balloon (balloon body) and the air within that balloon are greater than the upward buoyant force of the surrounding displaced air.
Experiment, Results and Conclusion
If an air-filled balloon is heated (as with a hair dryer or strong sunlight) the balloon will temporarily rise because the expanded and heated air inside the balloon increases, more air is displaced and there is now a greater upward buoyant force. When the balloon cools, it begins to descend.  This balloon comparison and experiment is important to think about and remember and is common to the hot-air balloon.

Water Displacement and Balloon Buoyancy for Virtual or Real Balloon Experiment

Here is another simple virtual or real experiment on buoyancy.

Materials and Methods
This part of a balloon experiment is similar to the cork experiment illustrated in the photo above with the exception that we are dealing with a larger object and a greater volume of water.
If any air- or helium-filled balloon is carefully and gently pushed downward into a bucket filled with water to the very rim, the water will overflow. If there is a catch-basin or plastic tarp available to catch the displaced water, then the water's volume or weight or both can be determined. Knowing this, we can determine the volume or weight of the water and convert that into the volume of the balloon based on the formula that 1 cc or 1 ml of water = 1 gram in weight. If a liter of water were displaced by the balloon there would be 1,000 cc or 1000 ml of water and the weight of water displaced would weigh 1,000 grams. As a means of comparison for those more familiar with quarts and gallons you can equate a quart as slightly less in volume than a liter and remember that 4 quarts make a gallon. A gallon of water weighs about 8.3 lbs. One pound is equivalent to 454 grams. Therefore, any object displacing 1,000 mls of water or 1,000 grams displaces 2.15 lbs of water.
Remember the volume of the helium in the balloon displaces that exact volume of water from the bucket as an overflow into the catch basin or tarp. Therefore, the volume of gas in the balloon can be measured and determined frm the overflow. If the balloon were a perfect sphere (which in our photo reveals it is not), we can also determine the balloon's volume based on the formula 4/3 x (3.14, the pi value) x radius cubed (r x r x r).

Helium Balloon Bouyancy and Mass-Weight Lift Experiment, – Real or Virtual Experiment

Our experiment is demonstrated and explained fully here with all the data. Your experiment can be done also and compared with our results.

Objective is to determine the buoyancy and the lifting power of a helium balloon and demonstrate the principle of buoyancy.

Materials and Methods
Helium-filled balloon, several paper clips, string or cord, scissors, notebook for data recording. Scale or balance that can measure mass (as weight here) in milligrams (mgs).

Remember that the string or ribbon has mass (weight) and this pulls downward due to the force of gravity.

1.   If possible, measure that mass by placing the string or ribbon on a balance and carefully hold the balloon in a way that permits almost all the string or  ribbon to be weighed by holding the balloon. Keep the balloon off to the side of the balance and do not exert any downward force with your hands (this can be done). Do not press on the balance in any way. Record the weight of the ribbon or ribbon and string.

2.   Record the weight of a paper clip.

3.   Take the helium balloon (usually with a ribbon or light string attached) and attach one known-weighted paper clip near the top of the ribbon or string used for tethering or holding the balloon.

4.   Observe if the balloon sinks or rises and write that into your lab book.  

5.   Continue to weigh and add one paper clip at a time to the other clip(s) on the balloon until the balloon either begins to sink or remain in equilibrium (neither rising, nor falling). Record and write down all the data.

Here is an actual experiment and pictures to show what happened in this experiment here at ScienceSuperSchool.

Balance weights (g = grams)):        Total Mass Pulling Down (g)     Balloon Activity

Ribbon only              0.3                           0.3                                         Rises  

Paper Clip 1 +          1.4                           1.7                                         Rises

Paper Clip 2 +          1.45                         3.15                                        Rises      

Paper Clip 3 +          1.35                         4.50                                        Sinks

Green String/ribbon  3.6                           3.90                                    Equilibrium

 

Results and Discussion

The balloon rises due to buoyancy. The weight of the ribbon is overcome by the buoyancy (lifting power) of the balloon. Therefore, the lift or buoyancy of the balloon is greater than 0.3 grams. When paper clips 1 and then 2 were added to the ribbon used to hold the balloon, upward lift (buoyancy) still existed. When paper clip 3 was added, the balloon sunk. This indicates that the lift of the balloon was greater than 3.15 grams, but less than 4.5 grams. When some green string and ribbon were tied together this caused the balloon to sink. However, when small segments of the green string were removed with scissors a point was reached where the balloon was in equilibrium (neither rising nor falling). At this point of equilibrium the upward and downward forces on the balloon were balanced. When the ribbon and the string were weighed together the total mass/weight was 3.9 grams. Therefore, this value of 3.9 grams represents the buoyancy or lift capacity of the helium balloon. Any addition to this would cause the balloon to sink. Any removal of excess string would cause the balloon to rise.

Conclusions

1.  A helium balloon has buoyancy and this is lifting power generated  when air is displaced by the balloon.

2.  The weight or mass of the balloon and all attachments exerts a downward force and this force is overcome by the lighter-than-air helium in the balloon which causes the balloon to rise.

3.  The balloon sinks when the weight of the balloon and any attachments exceeds the lifting buoyant force of the balloon.

 

Important links:
 
 
2. See  top of Home Page for Index-Directory of ScienceSuperSchool Articles
 
3. Links to still photos videos that highlight buoyancy facts and concepts here: (Note: Only experienced adults with highy technical skills should engage in any balloonist activities. Young people, teens and young adults need to be careful because balloonist lives have been lost due to piloted balloon accidents, miscalculations and mismanagement. 
 
a. A helium-cluster-balloon launch with "pilot" in strong protective harness and hot air balloon launch shown side by side.
(Pilot: John Ninomiya)
Wonderful still photos and embedded video of this flight.
 
b. Learn more and see more of John Ninomiya's activities here at clusterballoonist.org.
 
c. Hindenburg Update and News on Static Electricity and the Deadly Accident, March 5, 2013.There was a deadly explosion and fire aboard the hydrogen-laden Graf Zeppelin named the Hindenburg. During its attempted landing at the Lakehurst Naval Station, New Jersey, May 6, 1937 this very large dirigible caught exploded violently and caught fire. This was the flame seen round the word. Reuters reported on March 5, 2013 that this fire was induced by static electricity buildup on the zeppelin after the Hindenburg just after it had flown through a thunderstorm on the way to the landing and anchorage site at LakehurstBritish Pathe News did this fine photographic recording of the zeppelin and the actual accident. 

D. Goodyear helium-filled blimp basic information, still photos and videos to explore.

 

Buoyancy Articles at ScienceSuperSchool.com


Buoyancy Helium-Balloon Experiments and Fun with the Scientific Method



 
 
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