The Answer:
Airplanes are one of the most wondrous inventions ever created. A metal tube flying in the sky would have been inconceivable a couple hundred years ago. They rely on precise scientific principles to stay aloft. One mistake in the delicate engineering will result in the plane crashing down to the ground. But all of this is meaningless without a method of propulsion.
All the fancy scientific laws and theories combined with the best engineering cannot make a metal bird fly. Metal is heavy. Much heavier than the equivalent volume of air. It needs powerful thrust to be able to life off the ground. Thus, an adequate fuel source is needed.
In cars, the common fuel type is a petrol base. High quality petrol is used in cars now because of their engine needs. Higher quality means higher quality, longer output, which lets the car go longer on less. It also increases the longevity of the car, higher quality fuel causing less wear and tear on the engine block when used.
An airplane, especially massive passenger planes, need something a little more powerful than petrol to keep their engines running at peak efficiency. These engines use a material called aerial kerosene. Once the engine begins to burn the kerosene, it burns explosively, many times hotter and more powerful than pretty much any petrol derivative. It allows jets weighing thousands of tons to achieve flight. Fighter jets that use this fuel can break the sound barrier, reaching ridiculous speeds in the matter of seconds.
Airplanes, especially the larger jet varieties, have multiple, massive engines to propel them forward. The fuel needs for these engines are exorbitant. A Boeing-747 jumbo jet, one of the biggest planes in the world uses about a gallon of fuel per second. These planes can hold up to 90 tons of fuel. While for most trips this is overkill, there are some flights that require nearly this much fuel. In 1946, a South African jumbo jet had a non-stop flight of almost 10,000 miles. When it landed, it had enough fuel for another two-hour flight. That flight was in 1946. Today, planes burn fuel much more efficiently, using less per mile now than ever before.
Another reason for the exorbitant fuel capacity is safety. Standard flight protocol for bad weather at a landing site is for the plane to circle around the landing strip, preferably out of the affected area, until the weather calms down. Also to if the plane needs to make unexpected extensions to its flight in the case of an emergency, it needs to have extra fuel just in case. Flights crossing the Atlantic and Pacific oceans especially need this extra fuel. Again, weather can often play a factor here. Storms on the open sea are almost universally stronger and larger than ones on land. If a plane has to fly around a storm, it needs extra fuel to do so. The last thing airline companies, passengers, and the pilots want is the plane to crash because of a lack of fuel.
One interesting thing about a plane’s fuel tank, particularly for a massive passenger jet, is the physical location. They are placed in such a way near the wings (and the engines) that they balance the plane out. Afterall, imbalance can quickly lead to a loss of control by the pilot. The pilot also has the ability to control where the fuel goes to. For example, if a plane needs to make a long, wide turn, the fuel on one side of the plane will be burned faster than the other side while the turn is occurring. Imbalance will occur if the fuel is not actively shifted around to keep the same amount in every fuel tank.
Airplanes are fascinating machines. True wonders of technology.