Heat and temperature

Compared to the Sun, Earth has a much lower temperature and so sends far less thermal radiation back to the Sun. The heat of this process can be quantified by the net amount, and direction Sun to Earthof energy it transferred in a given period of time. In thermodynamicsheat is energy transferred from one system to another as a result of thermal interactions. Transfer of energy as heat can occur through direct contact, through a barrier that is impermeable to matter as in conductionby radiation between separated bodies, by way of an intermediate fluid as in convective circulationor by a combination of these.

Heat and temperature

Earlier in this lessonfive dictionary style definitions of temperature were given. The degree of hotness or coldness of a body or environment. A measure of the warmth or coldness of an object or substance with reference to some standard value.

A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. A measure of the ability of a substance, or more generally of any physical system, to transfer heat energy to another physical system.

Any of various standardized numerical measures of this ability, such as the Kelvin, Fahrenheit, and Celsius scale As mentionedthe first two bullet points have rather obvious meanings.

How does Temperature Differ from Heat?

The third bullet point was the topic of the previous page in this lesson. The fifth bullet point was the definition that we started with as we discussed temperature and the operation of thermometers; it was the topic of the second page in this lesson.

Heat and temperature

That leaves us with the Heat and temperature bullet point - defining temperature in terms of the ability of a substance to transfer heat to another substance. This part of Lesson 1 is devoted to understanding how the relative temperature of two objects affects the direction that heat is transferred between the two objects.

Consider a very hot mug of coffee on the countertop of your kitchen. What do you suppose will happen in this situation? I suspect that you know that the cup of coffee will gradually cool down over time.

Even the coffee mug will likely be too hot to touch. But over time, both the coffee mug and the coffee will cool down. Soon it will be at a drinkable temperature.

And if you resist the temptation to drink the coffee, it will eventually reach room temperature. So what is happening over the course of time to cause the coffee to cool down? The answer to this question can be both macroscopic and particulate in nature. On the macroscopic level, we would say that the coffee and the mug are transferring heat to the surroundings.

This transfer of heat occurs from the hot coffee and hot mug to the surrounding air. The fact that the coffee lowers its temperature is a sign that the average kinetic energy of its particles is decreasing.

The coffee is losing energy. The mug is also lowering its temperature; the average kinetic energy of its particles is also decreasing. The mug is also losing energy. The energy that is lost by the coffee and the mug is being transferred to the colder surroundings.

We refer to this transfer of energy from the coffee and the mug to the surrounding air and countertop as heat. In this sense, heat is simply the transfer of energy from a hot object to a colder object. What will happen to the cold can of pop over the course of time? Once more, I suspect that you know the answer.

The cold pop and the container will both warm up to room temperature. But what is happening to cause these colder-than-room-temperature objects to increase their temperature?

Is the cold escaping from the pop and its container? There is no such thing as the cold escaping or leaking. Rather, our explanation is very similar to the explanation used to explain why the coffee cools down.

There is a heat transfer. Over time, the pop and the container increase their temperature.Heat is a form of energy that can be transferred from one object to another or even created at the expense of the loss of other forms of energy.

To review, temperature is a measure of the ability of a substance, or more generally of any physical system, to transfer heat energy to another physical system.

Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a change of state that occurs without a change in temperature. Such a process may be a phase transition, such as the melting of ice or the boiling of water.

Heat is the total energy of molecular motion in a substance while temperature is a measure of the average energy of molecular motion in a substance. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object.

Heat transfer is generally described as including the mechanisms of heat conduction, heat convection, thermal radiation, but may include mass transfer and heat in processes of phase changes.

Heat and temperature

Convection may be described as the combined effects of conduction and fluid flow. Heat is the total energy of molecular motion in a substance while temperature is a measure of the average energy of molecular motion in a substance.

Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object. Adding heat to an ice-water slush will convert some of the ice to water without changing the temperature.

In general, whenever there is a change of state, such as the solid-liquid or the liquid-gas transition, heat energy can be added without a temperature change.

Temperature - Wikipedia