How people learnt to use fire

 Fire is considered as the first step to civilization. Before invention of fire primitive people would live like wildy. Consume without boiling is just like consume behaviour of wild animals. Peoples were dependent on hunting. They would move area to area due to hunting. Once, a amaging things they observed that to making sharp of their hunting tools with stone a fire spark is produced. Such things happens as same as friction of one stone with other stone. This is a conversion of mechanical force into energy. They learnt to produce fire.