|
|
The Iranian name for the new year holiday on the Persian calendar, occurring on the spring equinox.
|
|
A particle found in the nuclei of atoms, similar to a proton but with no electric charge. Among light nuclei (helium, carbon, nitrogen), the ones that are most stable contain equal numbers of protons and neutrons. In heavier elements, the most stable ones have majority of neutrons, growing with mass. Varieties of nuclei also exist ("isotopes") which have other ratios between their numbers of protons and neutrons, but when the departure from the "most stable ratio" becomes large, neutrons can convert to protons + electrons (or vice versa), producing one form of radioactivity.
|
|
A star (approximately sun-sized or larger), a remnant of a supernova explosion, in which gravity has caused all matter to collapse to a giant nucleus, composed only of neutrons. The collapse is also expected to greatly amplify any magnetic field present in the pre-collapse star, as well as speed up enormously any rate of rotation. It is believed that pulsars, pulsating radio sources with very precise pulsation periods, are neutron stars of radius about 10 km and rotation period about 1 second. Their magnetic axis spins and beams radio waves, in a way similar to the way a lighthouse beams its light. We detect pulsars when the Earth is in one of the directions swept by the beams.
|
|
Unit of force, the force which, when applied to one kilogram mass, causes an acceleration of 1 meter/sec2.
|
|
Three laws which form the foundation of classical mechanics, i.e. of the theory of ordinary motions (not motions on an atomic scale, covered by quantum mechanics, and not at velocities close to that of light, covered by relativity). The laws introduce the concepts of force and mass and state (in modern terms)
In the absence of forces, an object ("body") at rest stays at rest, and an object moving in a straight line with constant velocity persists in doing so.
A (small) body subject to a force accelerates; the acceleration is in the direction of the force and proportional to its magnitude, and inversely proportional to the mass of the body: F = ma.
Forces are produced in pairs, in opposite directions and equal magnitudes.
Newton's laws (2) and (3) in Mach's formulation reduce to:" When two small bodies act on each other, they accelerate in opposite directions and the ratio of their accelerations is always the same."
|
|
The breaking up of a heavy nucleus in two parts of comparable masses, typically, 1/3 and 2/3 of the original mass, associated with a great release of energy. Since both fragments have a positive electric charge, they repel each other vigorously, causing them to be ejected with great speed in opposite directions. The kinetic energy of that motion, ultimately converted to heat, is the source of the "nuclear energy" of fission.
|
|
The short-range forces acting on protons and neutrons in atomic nuclei. Two types actually exist, the "strong force" which holds nuclei together, and the "weak force" which determines the ratio between the numbers of protons and neutrons.
|
|
The process of releasing energy by combining hydrogen atoms to form helium, or more generally, to combine light nuclei into heavier ones. Nuclear fusion appears to be the source of the energy of the Sun and of stars.
|
|
Power obtained from nuclear fission in nuclear reactors, ultimately converted to electric power.
|
|
(atomic; plural: nuclei). The small concentration of protons and neutrons, positively charged, at the center of atoms. The nuclei of atoms are positively charged and contain by far most of their mass (all but about 0.05% or less).
|
|