please tell me" what is the main idea of the text?"

 

People use many sources of energy. Ancient people used only their arms, hands, and simple tools until they discovered fire. Later, people learned to use the energy of the wind to sail ships. Then they learned to use animals to do work. In the eighteenth and nineteenth centuries, people began to use machines. The first machines used steam. They burned coal to heat water. The hot water turned into steam, and the steam engine did the work. Later, people began to use the gasoline engine, and today people are using nuclear energy.

Energy is one of the basic concepts, or ideas, of physics. It is the ability to do work. Without energy we could not live. We need energy to work, and scientists are always looking for new sources of energy.