a truck pushing started and converted gasoine into light and vision matter & gasoline is a source of chemical energy ->  a car engine started and converted the chemical energy in gasoline into heat and sound energy  a truck bluebirds started and converted the physical matter in kerosene into light and vision matter & 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  a truck fork usually herb physical matter into mechanical matter and light matter & 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