Simple harmonic motion. In mechanics and physics, simple harmonic motion is a type of periodic motion where the restoring force is directly proportional to the displacement.
It can serve as a mathematical model of a variety of motions, such as the oscillation of a spring. In addition, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum as well as molecular vibration. Simple harmonic motion is typified by the motion of a mass on a spring when it is subject to the linear elastic restoring force given by Hooke's Law. The motion is sinusoidal in time and demonstrates a single resonant frequency. Fretting. The contact movement causes mechanical wear and material transfer at the surface, often followed by oxidation of both the metallic debris and the freshly exposed metallic surfaces.
Because the oxidized debris is usually much harder than the surfaces from which it came, it often acts as an abrasive agent that increases the rate of both fretting and a mechanical wear called false brinelling. Steel[edit] Fretting damage in steel can be identified by the presence of a pitted surface and fine 'red' iron oxide dust reminiscent of cocoa powder. Strictly this debris is not 'rust' as its production requires no water.
The particles are much harder than the steel surfaces in contact, so abrasive wear is inevitable; however, particulates are not required to initiate fret. Products affected[edit] There is a current focus on fretting research in the aerospace industry. Spiral of Theodorus. The spiral of Theodorus up to the triangle with a hypotenuse of √17 In geometry, the spiral of Theodorus (also called square root spiral, Einstein spiral or Pythagorean spiral)[1] is a spiral composed of contiguous right triangles.
It was first constructed by Theodorus of Cyrene. History[edit] Plato does not attribute the irrationality of the square root of 2 to Theodorus, because it was well known before him. Theodorus and Theaetetus split the rational numbers and irrational numbers into different categories.[3] Hypotenuse[edit] Each of the triangles' hypotenuses hi gives the square root of the corresponding natural number, with h1 = √2. Plato, tutored by Theodorus, questioned why Theodorus stopped at √17. 6174 (number) 6174 is known as Kaprekar's constant[1][2][3] after the Indian mathematician D.
R. Kaprekar. This number is notable for the following property: Take any four-digit number, using at least two different digits. (Leading zeros are allowed.)Arrange the digits in ascending and then in descending order to get two four-digit numbers, adding leading zeros if necessary.Subtract the smaller number from the bigger number.Go back to step 2. 9990 – 0999 = 8991 (rather than 999 – 999 = 0) 9831 reaches 6174 after 7 iterations: 8820 – 0288 = 8532 (rather than 882 – 288 = 594) 8774, 8477, 8747, 7748, 7487, 7847, 7784, 4877, 4787, and 4778 reach 6174 after 4 iterations: Note that in each iteration of Kaprekar's routine, the two numbers being subtracted one from the other have the same digit sum and hence the same remainder modulo 9.
Sequence of Kaprekar transformations ending in 6174 Sequence of three digit Kaprekar transformations ending in 495 Kaprekar number Bowley, Rover. "6174 is Kaprekar's Constant". Ultimate fate of the universe. The ultimate fate of the universe is a topic in physical cosmology.
Many possible fates are predicted by rival scientific theories, including futures of both finite and infinite duration. Xenu. Xenu (/ˈziːnuː/ ZEE-noo),[1][2][3] was, according to Scientology founder L.
Ron Hubbard, the dictator of the "Galactic Confederacy" who 75 million years ago brought billions[4][5] of his people to Earth (then known as "Teegeeack") in a DC-8-like spacecraft, stacked them around volcanoes and killed them using hydrogen bombs. Official Scientology scriptures hold that the essences of these many people remained, and that they form around people in modern times, causing them spiritual harm.[1][6] Summary[edit] A DC-8 aircraft in 2004.
Hubbard described Xenu's spacecraft as looking exactly like DC-8s without "fans" (meaning the jet engines, or turbofans).[21] Xenu was about to be deposed from power, so he devised a plot to eliminate the excess population from his dominions. Scientology doctrine[edit] In RJ67,[21] Hubbard then alludes to the devastating effect of Xenu's genocide: OT III also deals with Incident I, set four quadrillion[37] years ago.