Fluids and Thermal

We are going to investigate the forces acting between an object and a fluid. A fluid is a collection of molecules that are randomly arranged and held together by weak cohesive forces between molecules and also by forces exerted by the container holding the fluid. Both liquids and gases are fluids. We discussed such a situation briefly, when we considered the resistive forces on objects moving through fluids. We will discuss forces that fluids exert on objects that are at rest relative to the fluid. This discussion will lead to an important new quantity, pressure, and a force called the buoyant force, which is not a new type of force, but our familiar forces acting in a specific situation. We will also investigate the physics of moving fluids. Understanding the concepts of moving fluids is important for a wide range of applications, from plumbing systems to automobile aerodynamics to blood flow in veins and arteries.

Then we will direct our attention to the study of thermodynamics, which involves situations in which the temperature or state (solid, liquid, gas) of a system changes due to energy transfers. We will focus on the heat $Q$ and its effects on the thermal conditions of a system. We will also look at work $W$ performed on deformable systems, such as an enclosed gas, as well as electromagnetic radiation $T_{ER}$ across a system boundary. Each of these energy transfers can cause a change in the internal energy $E_{int}$ of the system, which we can relate to temperature.

Historically, the development of thermodynamics paralleled the development of the atomic theory of matter. By the 1820s, chemical experiments had provided solid evidence for the existence of atoms. At that time, scientists recognized that a connection between thermodynamics and the structure of matter must exist.

Thermodynamics also addresses more practical questions. Have you ever wondered how a refrigerator is able to cool its contents, or what types of transformations occur in a power plant or in the engine of your automobile, or what happens to the kinetic energy of a moving object when the object comes to rest? The laws of thermodynamics can be used to provide explanations for these and other phenomena.