The formula is used to measure the speed of ocean waves, like tsunamis, that have very long wavelengths relative to the depth of the water. Tsunamis can have wavelengths greater than 700 kilometers (the average ocean depth is 3-4 kilometers). The formula estimates the tsunami's speed while it is in deeper waters (as it approaches shallower coastal waters, the tsunami slows down, its wavelength shortens, and its height increases).
Head lice and their eggs (nits) soon perish if separated from their human host. Adult head lice can live only a day or so off the human head without blood for feeding. Nymphs (young head lice) can live only for several hours without feeding on a human.
They need human blood in order to survive. Head lice live for approximately 30 days on a host and a female louse may lay up to 100 nits (eggs). Head lice off of their human hosts will starve. The NPA suggests that, in most cases, a head louse will not survive for more than 24 hours off of its human host.