Conduction is explained by collisions between atoms or molecules, and the actions of loosely bound electrons.
Materials composed of atoms with "loose" outer electrons are good conductors of heat and electricity also. Because metals have the "loosest" outer electrons, they are the best conductors of heat and electricity.
The spontaneous transfer of heat is always from warmer objects to cooler objects. If several objects near one another have different temperatures, then those that are warm become cooler and those that are cool become warmer, until all have a common temperature.
If the matetials are in the same vicinity, they should have the same temperature, room temperature.
The metal feels cooler because it is a better conductor.
Wood, on the other hand, is a poor conductor.
In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter.
Conduction of heat is the transfer of energy within materials and between different materials that are in direct contact.
Materials that conduct heat well are known as heat conductors.
Liquids and gases generally make poor conductors.
An insulator is any material that is a poor conductor of heat and that delays the transfer of heat.
Air is a very good insulator.
Porous materials having many small air spaces are good insulators.
Insulation slows down heat transfer.
Convection currents stirring the atmosphere produce winds.
Some parts of Earth's surface absorb heat from the sun more readily than others.
The uneven absorption causes uneven heating of the air near the surface and creates convection currents.
In convection, heat is transferred by movement of the hotter substance from one place to another.
Another means of heat transfer is by movement of the hotter substance.
Convection, means of heat transfer by movement of the heated substance itself, such as by currents in a fluid.
Convection occurs in all fluids, liquid or gas. When the fluid is heated, it expands, becomes less dense, and rises. Cooler fluid then moves to the bottom, and the process continues. In this way, convection currents keep a fluid stirred up as it heats.
Convection currents are produced by uneven heating.
During the day, the land is warmer than the air, and a sea breeze results. At night, the land is cooler than the water, so the air flows in the other direction.
Rising warm air, like a rising balloon, expands because less atmospheric pressure squeezes on it at higher altitudes. As the air expands, it cools-just the opposite of what happens when air is compressed.
When a molecule collides with a molecule that is receding, itd rebound speed after the collision is less than before the collision.
Most of the heat from a fireplace goes up the chimney by convection. The heat that warms us comes to us by radiation.
In radiation, heat is transmitted in the form of radiant energy, or electromagnetic waves.
Radiation is energy transmitted by electromagnetic waves. Radiation from the sun is primarily light.
Radiant energy is any energy that is transmitted by radiation.
From the longest wavelength to the shortest, this includes:
•Radio waves
•Microwaves
•Infrared radiation
•Visible light
•Ultraviolet radiation
•X-rays
•Gamma rays
All substances continuously emit radiant energy in a mixture of wavelengths.
Objects at low temperatures emit long waves while objects at high temperatures emit shorter wavelengths.
Heat radiation is infrared radiation.
An infrared thermometer measures the infrared radiant energy emitted by a body and converts it to temperature.
The radiation emitted by the object provides the reading. The average frequency of radiant energy is directly proportional to the Kelvin temperature of the emitter.
Very hot objects emit radiant energy in the range of visible light.
Higher temperatures produce a yellowish light.
Good emitters of radiant energy are also good absorbers while poor emitters are poor absorbers.
A blue-hot star is hotter than a white-hit star, and a red-hot star is less hot. Since the color blue has nearly twice the frequency of red, a blue-hot star has nearly twice the surface temperature of a red-hot star.
The radiant energy emitted by the stars is called stellar radiation.
The surface of the sun has a high temperature. It emits radiant energy at a high frequency-much of it in the visible portion of the electromagnetic spectrum.
The surface of Earth, by comparison, is cool and the radiant energy it emits consists of frequencies lower than those of visible light.
Radiant energy emitted by Earth is called terrestrial radiation. Much of Earth's energy is fueled by radioactive decay in its interior. The source of the sun's radiant energy involves thermonuclear fusion in its deep interior.
Both the sun and Earth glow-the sun at high visible frequencies and Earth at low infrared frequencies.
A book sitting on your deskis both absorbing and radiating energy at the same rate. It is in thermal equilibrium with its environment. Now move the book out into the bright sunshine.
Because the sun shines on it, the book absorbs more energy than it radiates.
•It's temperature increases.
•As the book gets hotter, it radiates more energy.
•Eventually it reaches a new thermal equilibrium and it radiates as much energy as it receives.
•In the sunshine the book remains at this new higher temperature.
If you move the book back indoors, the opposite process occurs.
•The hot book initially radiates nore energy that it receives from its surroundings.
•It cools and radiates less energy.
•At a sufficiently lowered temperature, it radiates no more energy than it receives from the room.
•It has reached thermal equilibrium again.
Absorption and reflection are opposite processes.
•A good absorber of radiant energy reflects very little radiant energy, including the range of radiant energy we call light.
•A good absrober therefore appears dark.
•A perfect absorber reflects no raidant energy and appears perfectly black.
Good reflectors, on the other hand, are poor absorbers. Light-colored objects reflect more light and heat than dark-colored ones. In summer, light-colored clothing keeps people cooler.
Anything with a mirrorlike surface reflects most of the radiant energy it encounters, so it is a poor absorber of radiant energy.
The colder an object's surroundings, the faster the object will cool.
An object hotter than its surroundings eventually cools to match the surrounding temperature. Its rate of cooling is how many degrees its temperature changes per unit of time. The rate of cooling of an object depends on how much hotter the object is than the surroundings.
This principle is known as Newton's law of cooling. Newton's law of cooling states that the rate of cooling of an object is approximately proportional to the temperature difference between the object and its surroundings.
It apllies to conduction, convection, or radiation.
Newton's law of cooling also holds for heating.
If an object is cooler tha its surroundings, its rate of warming up is also proportional to the temperature difference.
Radiant energy that enters an opening has little chance of leaving before it is completely absorbed.
