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Like
all animals, we humans need energy to power our bodies
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to enable us to move, grow and stay healthy. We get that energy from plants and animals
- by eating them.
If we eat more food than we need, our body converts the excess energy into fat. Animals create their own fat energy stores, so their bodies have energy available all the time. The first people on Earth also used
the primary sources of energy available. They used the sun's light to see
where they were going and the sun's heat to stay warm. They built boats
with sails which used the wind to move them across the water.
Unfortunately these primary sources of energy are not continuous. At nighttime there is no light or heat. When the wind stops, a sailboat is becalmed. Humans discovered that they could have heat and light energy whenever they needed it by burning plants and converting their stored energy to fire. A campfire at night provides light and warmth, cooks food and keeps away wild animals that would like to use the energy stored in humans as their own food! As human tribes gradually stopped roaming as hunter-gatherers and began settling down in villages and growing their own crops, they found more ways to use the energy available. Mills were set up by rivers to make use of moving water energy to turn the grindstones which ground grain to flour. In some countries windmills were used for the same thing. Humans thrived and multiplied by using energy, but the more people there were, the more energy they needed! |