Applications of Physics in Balloons Essay

Although the history of aeronautics has just two hundred years, the human desire to break away from the ground and soar like a bird appeared in ancient times. Ability to fly was considered as something extraordinary, inherent to powerful wizards or gods. That was the reason why many of the gods were depicted as winged creatures. The desire to acquire an air sphere led to a number of projects, mostly unworkable. The man managed to realize his dream to fly under the clouds only when the Montgolfier brothers invented the first balloon.
Balloon designed by brothers Joseph and Jacques Montgolfier, which was made of linen and paper, filled with hot smoke, raised over Paris in 1783. Montgolfier brothers were convinced that their balloon went up due to the properties of air, charged with electricity, and that is why they were burning wet straw and wool at the neck of a balloon, considering that such smoke (“Montgolfier gas”) was endowed with those properties and it was effective only near the hearth of fire. Some time later a physicist Saussure disproved it. In 1783 a ” Charliиre” took off, it was a ball of physician Charles, filled with hydrogen. In 1784, Meunier and then the brothers Rober, designed the first pradirigibles with cycloidal air oars. That was the bright beginning of balloon (aircraft) history (Irving, 2009).
The flight of the balloon or airship in the air looks like a submarine diving under the water. If the mass of the aircraft, folded with the mass of the gas filling the shell, is less than the mass of air volume displaced by the apparatus, the ball goes up: if these masses are equal, the ball hangs still in the air, if the mass of the apparatus with the mass of the gas is more than the mass of displaced air, the ball omits. Thus, in order the flight to be possible, the mass of the aircraft without the gas should be less or equal to the difference of masses of light gas that fills the shell, and air in the same volume.
Archimedes’ law for gases explains the flight of the balloon, as the buoyancy force in it is not the same as in case of rigid body placed in gas. In fact, it is necessary to consider what forces influence balloon filled with light gas such as hydrogen. The lower part of the cover of the balloon is left open; the hydrogen pressure in the lower hole is equal to air pressure. Air pressure and the hydrogen pressure decreases with height, so as the air pressure and hydrogen pressure on different parts of the shell will be less than the pressure at the bottom holes, but the lighter hydrogen pressure decreases with height more slowly than the air pressure. Therefore, the envelope from the inside will feel more pressure, and the largest difference in pressure of hydrogen and air will be placed in the top of the cover. Consequently, the force acting on the dome of the cover inside and directed upwards, will be more than the power acting on the outside and directed downward; the difference between these forces will balance the weight of balloon, ie, cover, basket and cargo. Thus, the buoyant force is created here not due to the pressure difference at the lower and upper parts of the body (as in the case of solids), but because of the pressure difference inside and outside at the top of the cover.
At the very beginning of the flight the ball is filled with hydrogen so that the buoyant force exceeds the force of gravity: the weight of displaced air is more than the weight of the ball filled with gas, and that is why the ball flies up. When the ball reaches layers of air with less pressure, hydrogen is expanding and part of it can go outwards through the lower opening. Thus, at the height the outside air pressure also decreases the same as the hydrogen pressure inside the ball; the resultant force (buoyancy force) of these pressures decreases.
Finally, at a certain height the balloon rests in the balance. Weight of displaced air at such height is just equal to the weight of the ball with the inside gas. In order to return balloon to the ground, there is a need to release some gas from the shell, thus reducing displaceable volume of air. For this purpose there is a valve at the top part of cylinder which can be opened with the help of a rope from the basket of balloon. While opening the valve, the gas, having more pressure than the surrounding air is coming out. The valve at the bottom of the shell would not let the gas as the pressures of hydrogen and air are the same there.
The first balloons, invented in 1783 in France by Montgolfier brothers, were filled with hot air. Gases expand when heated, so the mass of heated air in the balloon is less than the repressed masses of cold air. But the density is low: when heated from 0 to 100 ° C – it is just 27% (Smith, 1999). Thus, the weight of the shell, baskets, crew and payload equals only 27% of the weight of air displaced by the shell. Therefore, even very large balloons had a small buoyant force. Soon after the invention of balloons, the French physicist Jacques Charles (1746-1823) proposed to fill the balloons with hydrogen, whose density is fourteen times less than the density of air. Hydrogen balloon has much more buoyant force than the air balloon of the same size.
The big disadvantage of hydrogen balloons is a flammability of hydrogen, which forms explosive mixture with air. Therefore, after the time when large natural sources of non-combustible light gas helium were found, the balloons and blimps are sometimes filled with helium. Filling the balloon with helium instead of hydrogen, people make it heavier on the 1 / 14 of its total weight. At this value the weight of the payload is decreased. The weight of shells, baskets, crew and payload equals 13/14 of hydrogen balloon while in helium it is 6 / 7 of the weight of displaced air (Rechs, 1987). Extra weight significantly reduces the height at which the balloon stops. Therefore, huge balloons, designed to fly at high altitude (stratospheric), are filled with hydrogen.
The fundamental law of hydrostatics (Pascal’s law) also influences the balloon. Pascal’s law states that the pressure produced at the stationary liquid or gas is transferred to any point of a liquid or gas equally in all directions. Pascal’s law influences the work of various hydraulic equipments: brake system, the press, etc. This law is a direct consequence of the absence of static friction forces in liquids and gases. Pascal’s law is inapplicable in the case of a moving fluid (gas), as well as in the case when the fluid (gas) is in a gravitational field, so it is known that the atmospheric and hydrostatic pressure decreases with height. Pascal’s law states that pressure in liquids and gases is spread evenly in all directions. So, when we inflate the balloon, it is inflated in all directions, and not just where we blow up. When we compress the inflated balloon, it can burst at any place, not only where we press.
Also describing physic processes, there is a need to mention the Newton’s Third Law states which that in all cases when a body acts on another, there is not a unilateral action but an interaction of bodies. Strengths of this interaction between the bodies have the same nature, appear and disappear simultaneously. While interaction of two bodies, both of them get acceleration, directed along the same line but in opposite directions. That is why the balloon always moves in the opposite direction from the air jet.
One more important physical law is Bernoulli’s law which states that for steady current flow (gas or liquid) the amount of pressure, kinetic energy per unit volume and potential energy per unit volume is constant at any point in the flow. Using this relation, which was formulated by Daniel Bernoulli, it is possible to determine the velocity of the fluid by measuring its pressure at two points (Cutler, 2005).
Motion of the gas obeys the law of conservation of mechanical energy. If to neglect viscosity and if the flow is moving in a straight line, this points to the creation of effect described by Bernoulli’s law: when the flow rate increases, the pressure decreases. This explains the well-known phenomenon that when the gas comes out of a hole (eg, chimney), it is sucked by wrapping it rapid flow of another gas.
Balloon is an aeronautic apparatus, which is lighter than air. The lift force of balloon is created by encased gas (or hot air) with a density less than the density of air (according to the law of Archimedes). Sorting out what makes the balloon to rise up, it is worth telling that the ball floats in the air for the same reason that fish swim in water. Each of them pushes out air or water around them, a lot more of their own.
If the balloon and its equipment weigh less than expelled air, it rises. If it loses some part of gas which raises it and its mass increases, it begins to fall. As the upward gas people use hot air, hydrogen or helium, because they are all lighter than conventional air.
A released ball will go up until the moment when the weight of displaced air equals its own. To change the height of flight, balloonist must either reduce the raising powers in order to descend, or to reduce its weight in order to fly up. To descend, he should release some gas through the valve at the top of the ball. To rise above, he must throw away a part of the load (ballast).
Hot air as a gas filling the balloon has several disadvantages. First, it quickly cools down and the balloon has to be constantly heated. Secondly, the range is limited by the amount of fuel, and place in a basket is not always enough. Finally, the hot air is only slightly lighter than a cool air. To provide sufficient buoyant force that lifts the balloon up, the machine has to have very large sizes. The diameter of the modern balloon reaches 25 meters.
To reduce the size of the balloon is possible if to use of light gas – hydrogen or helium. The first hydrogen balloon was built by Frenchman Jacques Alexander Cesar Charles (1746-1823) in 1783. Soon after the flight of Pilatre de Rozier and d’Arlanda, Charles rises into the air on his ballon, made of impermeable rubberized fabric and filled with hydrogen. In addition to progress in aeronautics, Charles is known for his works in physics.
As it was mentioned above, the balloon flies because its weight along with luggage and passengers is less than the weight of the displaced air. To maintain the temperature at the neck of the balloon the gas burner is installed. Improvement of cover of the balloon made it possible to use hydrogen as filler (it is 14.5 times lighter than air) and helium (7 times lighter than air) (Bhaskar, 2011).
It is worth telling about filling the balloons with helium. Helium is an unusual element.Atom of helium is a sturdy structure of molecules. To bare helium nucleus it is necessary to spend a record-high energy. Hence it has the lowest boiling point, the lowest heat of vaporization and melting and extreme volatility.
Germans were the first who started to use helium; they began to fill them with their zeppelins bombed London in 1915. Some time later helium started to attract increasing attention of chemists, metallurgists, machine builders and sellers of balloons. Currently, there are many technological operations (up to the individual stages of nuclear weapons) that can not be held in contact with air gases and are impossible without the use of protective helium environments.
Nowadays it is already a huge spread of balloons filled with helium. These balloons have a great volatility and therefore flying balls are always used on any holidays and birthday parties. They are associated with happiness and raise the mood of people that is why they became so popular.
It should also be noted that the balloon can burst if the pressure in it becomes too high. Also they can bust because while inflation of some balls, tension can be formed on the surface. If this tension is greater than the attraction of the molecules of rubber, the balloon can pop. It is impossible to make a completely flat, blank for the balloon with a uniformly distributed weight of the rubber.
Currently, the balloons (aircrafts) are used for needs of meteorology for sending the automatic weather stations at high altitudes. The emergence of modern gas-tight durable materials, gas burners, allowing keeping the heat inside the ball for a long time, made it possible to create balloons for sporting purposes also. Balloons (aircrafts) enabled humanity to discover Earth’s atmosphere. Traditional birthday balloons made people’s life bright and colorful. Balloon is a great invention of humanity which deserves to be used forever.