（1）In everyday usage “hot” means “having a lot of heat”. Many people think that “cold” in something completely separated from heat. But this is not true. Cold simply means “having very little heat”.（2）Your life depends on heat. In fact, every living thing depends on it. Without heat, every living thing would be frozen to death. All living things get their heat from the sun, which provides the conditions in which life is possible.（3）Since before the dawn of history, man has been able to make his own heat. He has been able to release the sun’s heat that is trapped in things such as wood, coal and oil. And he has been able to use this heat.（4）Heat has made civilization possible. With heat, man could melt metals. As man learned to use metals and fuels ,industries grew. As a result, engines were invented. These are machines that change heat energy into mechanical energy. Engines can do the work of many men. Without engines industrial civilization is impossible.（5）Yet when the first engines were built in the 17th c