Sonic boom is the loud noise created by the shock wave set up by an aircraft travelling at a speed faster than that of sound. Any plane in flight produces disturbances in the air through which it moves. As a result, pressure waves move out from points on the craft’s surface in much the same way as ripples spread out when a boat moves through water. These waves travel at the speed of sound and spread out ahead of the aircraft. If the plane travels at a subsonic speed the path ahead of the plane is cleared for it, so to say, and it never catches up with the pressure disturbance. However, at sonic speeds the sound waves and the aircraft are both travelling at the same speed and the waves cannot move ahead. As a result they pile up, reinforcing one another and this creates a high pressure shock wave, which causes the sonic boom.
The intensity of the sonic boom depends not only on the speed of the aircraft but also on the altitude at which it is cruising. The boom becomes less intense as the plane gains altitude.
Since the shock waves from a sonic boom can damage buildings, planes like the Concorde are not allowed to travel at supersonic speeds when flying over cities.
A sunspot is a relatively cooler region on the surface of the sun. For an observer on earth, sunspots appear as dark patches on the bright face of the sun. The number and size of sunspots on the sun’s surface keep changing. However, their numbers peak once in about eleven years. The peak-period during which the number of sunspots is very high is called the sunspot-maximum.
Superconductivity is a property which enables electricity to flow through a conductor without any loss. Normally, there is some loss of electricity as heat when current flows through a conductor. This is because atoms of the conductor resist the flow of electrons. The resistance, however, depends on the temperature. Thus, cold conductors conduct electricity better than hot conductors. But some conductors when cooled below a certain temperature called critical temperature, let electricity flow through them without any loss. In other words, they become superconductors. The critical temperature at which a material starts superconducting is specific to that material.
The word ‘UFO’ is an acronym for Unidentified Flying Objects. In other words, it is a flying object whose nature is not known. Weather balloons, certain types of clouds, high-flying aircraft, rocket stages, and the planet Venus have been often mistaken as UFOs. In common parlance, the term UFO has, however, come to mean an alien spacecraft. Also, there are some puzzling events and observations which have led to the speculation that some UFO sightings indicate the visits of alien or extraterrestrial beings from another world to earth. However, there is no technical evidence found to date which substantiates the belief. Astronomers are nevertheless continuing their search for extraterrestrial life in the universe.
Any sound of frequencies above the limit of human hearing, that is, 20,000 hertz or more, is called ultrasound. Ultrasound or ultrasonic waves are generated by devices called transducers that convert electrical, mechanical, or hydraulic energy into ultrasonic energy. The intense ultrasound waves generated by these devices can pack enough energy to break kidney stones (a process called lithotripsy); destroy harmful tissues in the brain and force dust and grease off delicate metal surfaces. They can cause liquids such as oil and water that normally would not mix to do so.
Virtual reality is a term used for the reconstruction of continuously changing scenes, as one would see them in real life, on a computer screen. It is basically an advanced version of computer graphics designed on the basis of real life or imaginary situations. The hardware and software required to simulate real time and real events on the computer are being developed. Logitech, the US hardware manufacturer has recently designed special computer mouse which will enable users to feed in three-dimensional (3D) spatial information into a computer. However, one would require special glasses to get a sense of screen depth and perceive the 3D effect. Computer modelling of 3D graphics has similarly become feasible.