Why computer is included in computer science?

The name stems from the purpose of a Computer, which is to compute (or calculate). A Computer is designed to compute, and this may be for purely mathematical purposes or for other applications, such as running scientific simulations or running computer games.

The Processor of modern Computers is the piece of hardware that computes, for instance, it could be given 3 and 5 and told to add them. The processor then computes the answer as 8. Of course, most Computers can handle far more complex calculations than this example.