By making some simple assumptions, such as the idea that matter is made of widely spaced particles in constant motion, the theory helps to explain the behavior of matter. Two important areas explained are the flow or transfer of heat and the relationship between pressure, temperature, and volume properties of gases.
Heat, Temperature, And Kinetic Theory
The summer sun can make it seem easy to understand the concepts of heat and temperature, at least in a visceral sense, but understanding what these concepts mean and how they interact in the more objective and codified world of physics is another matter entirely. For this, it is necessary first to begin to be far more careful when using the two terms, which are far from interchangeable when used in their strictest sense, as well as to develop an understanding of some of the basic and fundamental features of the physical world as it exists and as it is experienced. The following pages present a brief description and discussion of heat and temperature, and the physical/scientific contexts in which they can be properly understood. Armed with this understanding, one can talk about the temperature with much greater authority and with much greater interest than a mere discussion of climate.
A Kinetic Understanding of Heat and Temperature
There are some different contexts within which heat and temperature can be discussed even within the realm of physics, but typically when heat is mentioned it implies an invocation of the kinetic theory of matter. According to this theory, matter is composed of small particles -- atoms and molecules -- with varying amounts of space between them (NASA, n.d.). Gaseous matter has a great deal of space between the particles of which its made, liquid less so, and solid matter the least, generally speaking, and the particles are also in constant motion constrained by the space allowed in the form -- free-flowing for gases to very fixed for solids (Kurtus, 2011; NASA, n.d.Kurtus, 2011)).
Because all particles that make up mass are in motion, each of these particles clearly possesses some amount of energy; in reality, particles contain several types of energy that can have complex interaction, but for the understanding of temperature and heat the significant energy type is kinetic energy (Kurtus, 2011). Kinetic energy is determined by each individual particle within a given chunk of matter, with the mass of the particle itself times the square of its velocity being equal to that particle's kinetic energy (Kurtus, 2011). The sum of all of the kinetic energy within the chunk of matter -- that is, the kinetic energy of each and every particle that makes up the matter -- is the thermal energy of the matter, and it is here that heat and temperature can begin to be understood (Kurtus, 2011).
Heat can be used as another word for thermal energy, referring to the overall amount of thermal energy contained in a chunk of matter (IPAC, n.d.; Zobel, 2011). Temperature is a measurement of the average level of kinetic energy held by a particle in a given chunk of matter, or from a slightly different perspective is the thermal energy of the matter divided by the number of particles in the matter (Kurtus, 2011). Heat and temperature are thus closely related, bt while heat actually refers to energy in and of itself temperature simply refers to a measurement made (IPAC, n.d.). This marks an important distinction, especially as temperature is a measurment of an average amount of energy while heat, as energy in and of itself, refers to absolutes or totals, meaning that an object with greater mass would hold more heat than an object with smaller mass at the same temperature (IPAC, n.d.).
These definitions are related to the experience of "heat" as the term is typically used in day-to-day conversation. If an object (or "chunk of matter") has a temperature higher than body heat -- has an average level of kinetic energy that is higher than that of the human body, that is -- the object will feel "hot" when touched, and in fact will be transferring some of its energy to the body touching it -- this transfer of energy is what is experienced as "heat" (Kurtus, 2011). This helps to make the similarities and interactions between temperature and heat more clear, however they are still two very distinct and very different concepts. Put most simply, heat refers to the thermal energy stored by a mass in the form of the kinetic energy of the mass's particles, while temperature refers to a measurement of this energy taken as an average for each individual particle, such that the size of the mass affects the overall energy level (heat) but not the measurement of the average energy (temperature).
A variety of different factors affect the capacity that different substances and specific chunks of matter have for holding heat. The initial movement (i.e. kinetic energy) of the molecules in a substance are one factor, with greater freedom of movement allowing a chunk of matter to hold more heat; when the heat becomes to great for the particles in the matter to remain in the constraints of the matter, the matter might change form -- from a solid to a liquid or a liquid to a gas -- in order to achieve a higher heat capacity (DeLeon, n.d.). Different solids (and liquids and gasses) have their own heat capacities, in addition, which are impacted by molecular structure, crystal structure (if any), pressure, and other features at the molecular and atomic level (DeLeon, n.d.).
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