This involves cams, drive shafts, engines, and other moving parts. Mechanical engineers are interested in chemistry for some of the same reason as aerospace engineers. They need to create and use strong yet light weight metals and alloys. For example, if a car weighed in the range of eight tons it would be useless because it would accelerate extremely slow, need long breaking distances, and would be very inefficient. The amount of fuel and power needed to run the car would not be worth the benefits returned from the car. Mechanical engineers also use chemistry when deriving new fuels to be used in their state of the art power plants. These fuels are created from many new and rare combinations of propellants. The difference between the needs for aerospace engineers and mechanical engineers are minimal yet noticeable. While aerospace engineering focuses on a specific concept, mechanical engineering is used throughout every other engineering field. Mechanical engineers must understand the basic concepts of chemistry and all of the other engineering specialties. They are required to be able to work in groups and communicate effectively and efficiently. Communication is essential to being productive while working in a group. Since most engineers are forced to work in groups, communication is key. Another reason that chemistry is important to mechanical engineers is that they must produce alloys that can stand and absorb impacts equal to that of a car crash. Today, mechanical engineers are working on multiple types of projects. These projects involve creating and improving new and old parts of motion. They are striving to create an efficient yet durable product at the lowest cost available. This is very tricky because on a normal basis, the lower the cost the lower the quality of the product. In today's world, a balance of quality versus cost must be found that suit both the producer and the consumer.