Sentence:  Energy has seldom been found where we need it when we want it. Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to <WSD>kindle</WSD> a flame. 
Meaning of the word marked with <WSD> tags:  To start (a fire) or light (a torch, a match, coals, etc.).