Atomic clocks are quite complex, but the basic theory is simple: the transitions of a cesium atom as it moves back and forth between two energy levels are counted to keep time
The basenji, an African wolf dog, is the only dog that cannot bark.
The first film director to discover Hollywood was D.W. Griffith, who filmed In Old California there in 1910. California was ideal for early films partly because its reliable weather and bright sunlight - but also because it was as far as possible from Thomas Edison, who held most of the patents relating to motion pictures.
Dementia is not inevitable as you age. An American study of centenarians (those who reach the age of 100) found that 30 per cent of them worldwide reach the age of 100 cognitively intact. Unfortunately, that does mean that if you reach the age of 100 there is a 7 in 10 chance that you will suffer from dementia.
Skydivers reach a terminal velocity of about 120 miles per hour (190 km/hr) if they spread eagle themselves to maximise their air resistance, but a velocity of 150 mph (240 km/hr) if they assume a head-down position like a high-board diver about to enter the water.
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