Fluid mechanics is a branch of physics that deals with the study of fluids and their behavior under different conditions.All the fluids are substances that can flow and take the shape of their container. This article is an introduction to basic ideas of fluid mechanics, including the properties, classifications, principles, and applications of fluid mechanics.A fluid is a substance that is able to flow and takes the form of its container. In a broader sense, it is of two types: liquid and gas. Liquids are incompressible and have a definite volume, while gases are compressible and do not have a definite volume. Water, air, and oil are some examples of fluids occurring in nature.