By the beginning of the 20th century, Newton's law of universal gravitation had been accepted for more than two hundred years as a valid description of the gravitational force between masses. In Newton's model, gravity is the result of an attractive force between massive objects. Although even Newton was troubled by the unknown nature of that force, the basic framework was extremely successful at describing motion. (Full article...)
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Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo. The magnitude of Earth's magnetic field at its surface ranges from 25 to 65μT (0.25 to 0.65G). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11° with respect to Earth's rotational axis, as if there were an enormous bar magnet placed at that angle through the center of Earth. The North geomagnetic pole actually represents the South pole of Earth's magnetic field, and conversely the South geomagnetic pole corresponds to the north pole of Earth's magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward Earth's South magnetic field, i.e., the North geomagnetic pole near the Geographic North Pole). As of 2015, the North geomagnetic pole was located on Ellesmere Island, Nunavut, Canada.
While the North and South magnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, Earth's field reverses and the North and South Magnetic Poles respectively, abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics. (Full article...)
Bradbury took charge at Los Alamos at a difficult time. Staff were leaving in droves, living conditions were poor and there was a possibility that the laboratory would close. He managed to persuade enough staff to stay, and got the University of California to renew the contract to manage the laboratory. He pushed continued development of nuclear weapons, transforming them from laboratory devices to production models. Numerous improvements made them safer, more reliable and easier to store and handle, and made more efficient use of scarce fissionable materiel. (Full article...)
The essential nature of the atomic nucleus was established with the discovery of the neutron by James Chadwick in 1932 and the determination that it was a new elementary particle, distinct from the proton. (Full article...)
Insects are the only group of invertebrates that have evolved wings and flight. Insects first flew in the Carboniferous, some 350 to 400million years ago, making them the first animals to evolve flight. Wings may have evolved from appendages on the sides of existing limbs, which already had nerves, joints, and muscles used for other purposes. These may initially have been used for sailing on water, or to slow the rate of descent when gliding.
Two insect groups, the dragonflies and mayflies, have flight muscles attached directly to the wings. In other winged insects, flight muscles attach to the thorax, which make it oscillate in order to induce the wings to beat. Of these insects, some (flies and some beetles) achieve very high wingbeat frequencies through the evolution of an "asynchronous" nervous system, in which the thorax oscillates faster than the rate of nerve impulses. (Full article...)
A frog battery is an electrochemical battery consisting of a number of dead frogs (or sometimes live ones), which form the cells of the battery connected in a series arrangement. It is a kind of biobattery. It was used in early scientific investigations of electricity and academic demonstrations.
The principle behind the battery is the injury potential created in a muscle when it is damaged, although this was not fully understood in the 18th and 19th centuries; the potential being caused incidentally due to the dissection of the frog's muscles. (Full article...)
In 1904–1905, the Wright brothers developed their flying machine to make longer-running and more aerodynamic flights with the Wright Flyer II, followed by the first truly practical fixed-wing aircraft, the Wright Flyer III. The brothers' breakthrough was their creation of a three-axis control system, which enabled the pilot to steer the aircraft effectively and to maintain its equilibrium. This method remains standard on fixed-wing aircraft of all kinds. From the beginning of their aeronautical work, Wilbur and Orville focused on developing a reliable method of pilot control as the key to solving "the flying problem". This approach differed significantly from other experimenters of the time who put more emphasis on developing powerful engines. Using a small home-built wind tunnel, the Wrights also collected more accurate data than any before, enabling them to design more efficient wings and propellers. Their first U.S. patent did not claim invention of a flying machine, but rather a system of aerodynamic control that manipulated a flying machine's surfaces. (Full article...)
The original form of Newton's second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. If the mass of the object is constant, this law implies that the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. (Full article...)
Image 30One possible signature of a Higgs boson from a simulated proton–proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines. (from History of physics)
Image 40Classical physics is usually concerned with everyday conditions: speeds are much lower than the speed of light, sizes are much greater than that of atoms, yet very small in astronomical terms. Modern physics, however, is concerned with high velocities, small distances, and very large energies. (from Modern physics)