sentences: a car engine started and converted gasoine into heat and sound energy & gasoline is a source of chemical energy ->  a car engine started and converted the chemical energy in gasoline into heat and sound energy  a car engine started and converted the chemical energy in gasoline into heat and sound energy & sound is a kind of mechanical energy ->  a car engine usually converts chemical energy into mechanical energy and heat energy  a car engine usually converts chemical energy into mechanical energy and heat energy & when one kind of energy changes into another kind of energy , the total amount of energy is constant -> when the car engined started the total amound of energy is constant