Valve ndi chinthu chowongolera chowongolera.Podutsa valavu, sing'anga yogwirira ntchito imatha kuyenda motsatira njira yomwe mwapatsidwa.Pogwira ntchito, pomwe mayendedwe apakati akusintha.Valavu imagwira ntchito kuyimitsa kubwerera kwa meduim mu dongosolo.Choncho, mankhwala amatchedwanso valavu osabwerera.