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Time travel is a concept in philosophy and fiction, particularly science fiction. In fiction, time travel is typically achieved through the use of a device known as a time machine. The idea of a time machine was popularized by H. G. Wells's 1895 novel The Time Machine. [1] It is uncertain whether time travel to the past would be physically ...
Time travel can result in multiple universes if a time traveller can change the past. In one interpretation, alternative histories as a result of time travel are not parallel universes: while multiple parallel universes can co-exist simultaneously, only one history or alternative history can exist at any one moment, as alternative history usually involves, in essence, overriding the original ...
Super-fast express: Any passenger train with an average speed higher than 55 km/h (34 mph) on 1,676 mm (5 ft 6 in) broad gauge. b. Mail: Trains which earlier had a mail coach attached. Newer trains are not named so, but older trains remain in operation. c. Express: Express trains travel faster and have fewer stops than ordinary passenger trains.
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air, is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s.
Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph). For air and marine travel, the knot is commonly used. The fastest possible speed at which energy or ...
Speed, the scalar magnitude of a velocity vector, denotes only how fast an object is moving, while velocity indicates both an object's speed and direction. [3] [4] [5] To have a constant velocity, an object must have a constant speed in a constant direction. Constant direction constrains the object to motion in a straight path thus, a constant ...
Duronto Express, translating to "restless" in Bengali, is a class of long-distance rapid trains operated by Indian Railways.Initially conceived to operate non-stop between origin and destination stations, since January 2016, these trains have been permitted to make additional commercial stops and accept ticket bookings from technical halts.
The two-way speed of light is the average speed of light from one point, such as a source, to a mirror and back again. Because the light starts and finishes in the same place, only one clock is needed to measure the total time; thus, this speed can be experimentally determined independently of any clock synchronization scheme.