Simplify the following text for a Grade 11 native English-speaking person.
Original: The conservation of mechanical energy is a principle which states that under certain conditions , the total mechanical energy of a system is constant .
Simplified: The law of conservation of mechanical energy states that if a body or system is subjected only to conservative forces the total mechanical energy of that body or system remains constant . In an isolated system where only conservation forces are acting , the total mechanical energy is conserved .