You鈥檙e at a birthday party and the place is full of helium-filled balloons stuck to the ceiling. How are these balloons defying gravity? No magic involved! The law of buoyancy as first stated in the third century BC by Archimedes is at work: Any object, totally or partially immersed in a fluid or liquid, is buoyed up by a force equal to the weight of the fluid displaced by the object. Helium is lighter than air, so a balloon filled with this gas weighs less than the air it displaces and will therefore be subjected to an upward force.
In 1868, French astronomer Pierre Jules C茅sar Janssen, while observing a solar eclipse with a device known as a spectroscope, noticed a line in the spectrum of sunlight that could not be matched to that of any known element at the time. A couple of months later, the English astronomer Joseph Norman Lockyer, also noticed this line, and named the new element helium after the Greek god of the sun, Helios.
In 1882, Italian physicist Luigi Palmieri was analyzing lava from the eruption of Mount Vesuvius and noticed this same spectral line, which indicated that helium was not only present in the sun鈥檚 atmosphere, but also on Earth.
The presence of helium on Earth was further confirmed in 1895, when Scottish chemist William Ramsey treated a naturally occurring ore of uranium, cleveite, with an acid and noted the evolution of a gas whose spectrum matched that of helium.
The helium used nowadays comes mostly from the radioactive decay of elements such as uranium and thorium, and is extracted from underground deposits. It has countless uses besides being used to fill party balloons! Helium is used in the production of fiber optic cables, which are used to provide internet and TV access, and in semiconductor chips that are found in most electronic devices. It is also used to cool the superconducting magnets that are an integral part of MRI imagers. The large hadron collider in Switzerland also relies on huge amounts of liquid helium to cool its superconducting magnets. Blimps and scientific research balloons are also buoyed by helium and the gas is combined with oxygen to form a mixture known as heliox, which reduces airflow resistance and is used in the treatment of upper airway obstruction. Recently magician David Blaine in the Arizona desert holding onto fifty-two helium-filled balloons before skydiving back to earth. Obviously a fan of Archimedes.
Caitlin Bard is completing her Bachelor of Science with a major in聽neuroscience聽at 成人VR视频.
