Mechanical engineering is the application of physical and scientific principles for solving the problems of society`s with regarding to Mechanical Systems (Preaty Much Everything that Moves and Stops).
The Invention of Wheel is one of the oldest root of the Mechanical Engineering. Because circular motion is most general requirement and the key invention that make huge impact to revolunised the field is Thomas Newcoman`s Steam Engine. that also key creation behind Industrial Revolution as well.
And so the most basic need of Mechanical Engineers are for creating tools for Industial Menufacturing Machines (Drillers,Cutters,Fabiricators,Rollers,Compressor),Vehicles,Moters, etc...
And Most Basic study subjects for Mechanical Engineers are materials science,Physics,Mathamatics most specifically Geometery and Calculaus.