Physics

Johannes Kepler formulated the three laws of planetary motion, describing the orbits of planets around the sun. This distinguishes him from Copernicus, who proposed heliocentrism, Newton, who formulated the law of universal gravitation, and Galileo, who made significant astronomical observations but did not enunciate these laws.

According to Einstein's theory of relativity, the speed of light in a vacuum is always constant and does not change regardless of the observer's frame of reference. Length, time, and space can vary depending on relative motion, but the velocity of light remains invariant.

The first controlled nuclear fission of an atom was carried out in Germany in 1938 by Otto Hahn and Fritz Strassmann, who discovered nuclear fission of uranium. This discovery marked the beginning of nuclear physics research leading to controlled fission.

The Doppler effect applies to both light waves and sound waves, as it describes the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the waves.

An Angstrom is a unit of length equal to 10^-10 meters, commonly used to measure atomic and molecular scales, such as wavelengths of light and sizes of atoms.

The SI unit of illumination is the lux, which measures luminous flux per unit area. Candela is the unit of luminous intensity, and flux refers to luminous flux measured in lumens.

A pulsar is a highly magnetized, rotating neutron star that emits beams of electromagnetic radiation. This radiation can be observed when the beam is pointed toward Earth, making neutron stars the correct identification for pulsars.

Adiabatic demagnetisation is a principle used to achieve very low temperatures by reducing the magnetic field on certain materials, causing their temperature to drop. This method is commonly used in cryogenics to reach temperatures near absolute zero.

Among the four fundamental forces, gravitational force is the weakest. Electrostatic, magnetic, and nuclear forces are significantly stronger at the particle level.

The velocity of sound in air primarily depends on temperature, moisture content, and wind conditions. However, under normal atmospheric conditions, changes in air pressure do not significantly affect the speed of sound because both the density and elasticity of air change proportionally, leaving the speed nearly constant.