A door hinge is considered a simple machine because it is classified as a lever. Hammers and bottle openers are also examples of simple machines.
A simple machine is defined as a type of machine that has very few or no moving parts. These machines are designed to make work easier for an array of applications. Other examples of simple machines include gears, pulleys and wedges. All of these types of simple machines work differently, but they consist of a few simple parts that do not operate mechanically. Simple machines are found in everyday life and include wheels, knives, seesaws, clamps and zippers.