What do mechanical engineers actually do?

Hello Anne! These are great questions - the trick is that Mechanical Engineering is one of the broadest engineering fields, so it's tough to answer what a mechanical engineer "actually does." One way to think about it is that mechanical engineers work on every physical scale - from designing nano- and micron-sized devices all the way up to analyzing the movements of huge fluid bodies like the air in our atmosphere - and everything in between. 

So some mechanical engineers work with calculus every day, but many mechanical engineers may not use calculus at all. Another way to think about it is that mechanical engineers are always solving problems, using modern tools and computing power to help them as needed. With sophisticated CAD programs and simulation software some mechanical engineers may never use calculus directly, but are informed by it in setting up a computational fluid dynamics scenario or finite-element analysis, for instance. 

Similarly some mechanical engineers may do a great deal of design work, while others instead validate and test new designs. Literally inventing something new is less common than you might think in engineering overall - a lot of mechanical engineering and engineering in general is the process of refining and improving an existing product to be less expensive or more reliable. Mechanical engineers may invent new materials or maybe they demonstrate how an existing material can be used in a new way! There's endless ways to be an engineer aside from making new things, so I encourage you to take a broad definition of "inventing" and "engineering" alike. 

Most engineers in industry work on teams, as it is rare these days for anything to be created in isolation. Mechanical engineers often interface with electrical engineers, software engineers, quality engineers, manufacturing engineers, machinists, technicians, marketing, customer service, and much more. They can be a part of most any kind of team - engineering and beyond. 

Finally, keep in mind that your experience as an engineering student may be very different than your experience as an engineer. Depending on your specific institution and program, you may have a lot of math and science fundamentals with a few engineering projects and hands-on experiences. These are meant to help prepare you for work in industry, but by no means can they teach you everything you'll need to learn once you go to work. Ideally (to me), engineering school helps you learn how to learn and how to analyze and approach problems. These skills are helpful for any future career path you choose! I also encourage you to do an internship while you are in school, either during the summer or balanced with your coursework. An internship will give you invaluable experience and show you first-hand what an engineering corporation is like, and getting to know working engineers will also help you know what to expect as an engineer compared to an engineering student.