How black holes are detected?
One way of finding black holes is to observe the matter moving around in an orbit at much higher speed than expected. By carefully mapping this motion, the third law of Kepler and Newton’s law of gravitation can be applied without seeing the actual object at the centre of the orbit.
Another way of finding black holes is to look at them as sources of X-ray radiation. The tremendous gravitational field of the black hole can produce huge amounts of light nearby and around itself even if it itself is black. Just as a meteorite or spacecraft gets hot as it enters the Earth’s atmosphere, the falling matter gets hot from the frictional drag too; sometimes reaching temperatures of millions of degrees. That hot material glows brightly and emits far more X-ray radiation and radio waves than would normally be expected from such a small volume of space. Scientists search for such small spaces with abnormally high X-Ray radiation to look for black holes.
Does hot water freeze faster than cold?
A bucket of hot water will not freeze faster than a bucket of cold water. However, a bucket of water that has been heated or boiled, then allowed to cool to the same temperature as the bucket of cold water, may freeze faster. Heating or boiling drives out some of the air bubbles in water; because air bubbles cut down thermal conductivity, they can inhibit freezing. For the same reason, previously heated water forms denser ice than unheated water, which is why hot-water pipes tend to burst before cold water pipes.
What is superconductivity?
Superconductivity is a condition in which many metals, alloys, organic compounds, and ceramics conduct electricity without resistance, usually at low temperatures. Heinke Kamerlingh Omnes, a Dutch physicist, discovered superconductivity in 1911. The modern theory regarding the phenomenon was developed by three American physicists—John Bardeen, Leon N. Cooper and John Robert Schrieffer. Known as the BCS theory after the three scientists, it postulates that superconductivity occurs in certain materials because the electrons in them, rather than remaining free to collide with imperfections and scatter, form pairs that can flow easily around imperfections and do not lose their energy. Bardeen, Cooper and Schrieffer received the Nobel Prize in Physics for their work in 1972. A further breakthrough in superconductivity was made in 1986 by J. Georg Bednorz and K. Alex Müller. Bednorz and Müller discovered a ceramic material consisting of lanthanum, barium, copper and oxygen which became superconductive at 35°K (–238°C)—much higher than any other material. Bednorz and Müller won the Nobel Prize in Physics in 1987. This was a significant accomplishment since in most situations the Nobel Prize is awarded for discoveries made as many as 20 to 40 years earlier.
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What is the speed of sound?
The speed of sound is not a constant; it varies depending on the medium in which it travels. The measurement of sound velocity in the medium of air must take into account many factors, including air temperature, pressure and purity. At sea level and 32°F (0°C), scientists do not agree on a standard figure; estimates range from 740 to 741.5 miles (1,191.6 to 1,193.22 kilometres) per hour. As air temperature rises, sound velocity increases. Sound travels faster in water than in air and even faster in iron and steel. Sounds travelling a mile in air for five seconds will travel the same distance in one second under water and one-third of a second in steel.
Why do golf balls have dimples?
The dimples minimize the drag (a force that makes a body lose energy as it moves through a fluid or gas), allowing the ball to travel farther than a smooth ball would travel. The air, as it passes over a dimpled ball, tends to cling to the ball longer, reducing the eddies or wake effects that drain the ball’s energy. A dimpled ball can travel up to 300 yards (275 metres), but a smooth ball only goes 70 yards (65 metres). A ball can have 300 to 500 dimples that can be 0.01 inch (0.25 millimetre) deep. Another effect to get distance is to give the ball a backspin. With a backspin there is less air pressure on the top of the ball, so the ball stays aloft longer (much like an airplane).