A mechanical engineer works with the principles of motion, energy, and force. Usually a machine transforms one form of movement into another. Mechanical engineers design machines whose parts function safely, reliably, and efficiently. Mechanical engineers apply the scientific method to find answers to mechanical problems. Many laws and principles developed by scientists are used every day by the mechanical engineer. Mechanical engineers contribute to many industries and occupations. Some mechanical engineers work in areas that are not usually thought to require engineering. Efforts to clean up and preserve the earth's environment have led many mechanical engineers to projects involving the treatment of water, soil, and waste materials. Mechanical engineers also work with doctors, therapists, and other medical professionals to study how the human body works and design aids and tools for mechanics. Mechanical engineers work in industry, consultancy firms, universities and government research. Most mechanical engineers work in industry at equipment manufacturers, aerospace companies, utilities, and many other large and small companies. Job responsibilities range from basic research and system design to power plant operation and quality control. Mechanical engineers earn good salaries. A novice engineer with a bachelor's degree can earn $40,000 a year. The average salary for an engineer is over $65,000. Earnings depend on experience and training. The government tends to pay its engineers slightly less than the going rate in private industry. Large companies that have high levels of mechanical engineering usually offer comprehensive benefits packages. Benefits include health insurance, life insurance, paid sick leave, paid holidays and vacations, and travel expenses.