10 most difficult physics riddles

And cosmic velocity - also referred to as the circular velocity, it is the speed that should be given to the body to enter into orbit around Earth. If a rocket launches from the surface of the earth, then it has to get at least 7.9 kilometers per second to get into orbit.

Water gas is a mixture of carbon monoxide and hydrogen produced from synthesis gas. Synthesis gas is a useful product, but requires careful handling due to its flammability and the risk of carbon monoxide poisoning. The water-gas shift reaction can be used to reduce the carbon monoxide while producing additional hydrogen, resulting in water gas.

Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost.

The Ku band is the portion of the electromagnetic spectrum in the microwave range of frequencies from 12 to 18 gigahertz (GHz). Ku band is primarily used for satellite communications, most notably for fixed and broadcast services, and for specific applications such as NASA's Tracking Data Relay Satellite used for both space shuttle and International Space Station

Nuclear fission of heavy elements was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann, and explained theoretically in January 1939 by Lise Meitner and her nephew Otto Robert Frisch

The Armstrong limit or Armstrong's line is a measure of altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. Humans absolutely cannot survive above this limit in an unpressurized environment. Above Earth, this begins at 18–19 km (11–12 mi; 59,000–62,000 ft) above sea level. The term is named after United States Air Force General Harry George Armstrong, who was the first to recognize this phenomenon

Radioactive nickel-56 (which decays to the most common isotope of iron) is the last element to be produced before the collapse of a supernova. That is why the iron was abundantly scattered into space after the supernova explosion.

210Po is extremely toxic, with one microgram being enough to kill the average adult (250,000 times more toxic than hydrogen cyanide by weight). 210Po was used to kill Russian dissident and ex-FSB officer Alexander V. Litvinenko in 2006.

Sir William Lawrence Bragg was an Australian-born British physicist and X-ray crystallographer, discoverer of Bragg's law of X-ray diffraction, which is basic for the determination of crystal structure. Bragg was, until October 2014, the youngest ever Nobel laureate; he won the prize in 1915 at the age of 25. He remains the youngest recipient of the Physics Prize.

Auxetics are structures or materials that have a negative Poisson's ratio. When stretched, they become thicker perpendicular to the applied force. This occurs due to their particular internal structure and the way this deforms when the sample is uniaxially loaded. Auxetics can be single molecules, crystals, or a particular structure of macroscopic matter.