Instead, heat is transferred in infrared waves part of the electromagnetic spectrum. Heat waves radiate out from hot objects in all directions, travelling at the speed of light, until they hit another object. When this happens, the heat energy carried by the waves can be either absorbed or reflected. Fire illustrates the three different methods of heat transfer. For example, the firebox will heat up due to convection. The air above the fire will be warm due to convection. You can warm your hands near to the flames due to radiant heat transfer.
When gases, liquids and solids are heated, they expand. As they cool, they contract or get smaller. The expansion of the gases and liquids is because the particles are moving around very fast when they are heated and are able to move further apart so they take up more room. If the gas or liquid is heated in a closed container, the particles collide with the sides of the container, and this causes pressure.
The greater the number of collisions, the greater the pressure. Sometimes when a house is on fire, the windows will explode outwards. This is because the air in the house has been heated and the excited molecules are moving at high speed around the room. They are pushing against the walls, ceiling, floor and windows.
Because the windows are the weakest part of the house structure, they break and burst open, releasing the increased pressure. Add to collection. Go to full glossary Add 0 items to collection. Download 0 items. Twitter Pinterest Facebook Instagram. Cool Facts Ever burnt your hand from picking up something hot? Teacher's Toolkit Take this to the classroom! Curriculum ready content.
Unit Plan Water for Life. Year 2. Lesson 3. Unit Plan Forms of Energy. Year 8. Lesson 1. Unit Plan Heat from the Sun. Year 3. Lesson 7 - 8. Lesson 11 - Unit Plan Energy Transfer. Year 9. Lesson 2 - 4. For the moment, we will confine our attention to joule and calorie. Heat and work are both measured in energy units, but they do not constitute energy itself. As we will explain below, they refer to processes by which energy is transferred to or from something— a block of metal, a motor, or a cup of water.
When a warmer body is brought into contact with a cooler body, thermal energy flows from the warmer one to the cooler until their two temperatures are identical. This is a misnomer; heat is a process and is not something that can be contained or stored in a body.
It is important that you understand this, because the use of the term in our ordinary conversation "the heat is terrible today" tends to make us forget this distinction. There are basically three mechanisms by which heat can be transferred: conduction, radiation, and convection. The latter process occurs when the two different temperatures cause different parts of a fluid to have different densities.
Work , like energy, can take various forms: mechanical, electrical, gravitational, etc. All have in common the fact that they are the product of two factors, an intensity term and a capacity term.
For example, the simplest form of mechanical work arises when an object moves a certain distance against an opposing force. Electrical work is done when a body having a certain charge moves through a potential difference. Performance of work involves a transformation of energy ; thus when a book drops to the floor, gravitational work is done a mass moves through a gravitational potential difference , and the potential energy the book had before it was dropped is converted into kinetic energy which is ultimately dispersed as thermal energy.
Heat and work are best thought of as processes by which energy is exchanged, rather than as energy itself. So you can think of heat and work as just different ways of accomplishing the same thing: the transfer of energy from one place or object to another. Into one container you place an electrical immersion heater until the water has absorbed joules of heat. The second container you stir vigorously until J of work has been performed on it.
At the end, both samples of water will have been warmed to the same temperature and will contain the same increased quantity of thermal energy.
There is no way you can tell which contains "more work" or "more heat". A gas engine converts the chemical energy available in its fuel into thermal energy. Only a part of this is available to perform work; the remainder is dispersed into the surroundings through the exhaust. This limitation is the essence of the Second Law of Thermodynamics which we will get to much later in this course. Thermal energy is very special in one crucial way. All other forms of energy are interconvertible : mechanical energy can be completely converted to electrical energy, and the latter can be completely converted to thermal, as in the water-heating example described above.
But although work can be completely converted into thermal energy, complete conversion of thermal energy into work is impossible. A device that partially accomplishes this conversion is known as a heat engine ; a steam engine, a jet engine, and the internal combustion engine in a car are well-known examples. We all have a general idea of what temperature means, and we commonly associate it with "heat", which, as we noted above, is a widely misunderstood word.
Both relate to what we described above as thermal energy —the randomized kinetic energy associated with the various motions of matter at the atomic and molecular levels. Heat , you will recall, is not something that is "contained within" a body, but is rather a process in which [thermal] energy enters or leaves a body as the result of a temperature difference. So when you warm up your cup of tea by allowing it to absorb J of heat from the stove, you can say that the water has acquired J of energy — but not of heat.
If, instead, you "heat" your tea in a microwave oven, the water acquires its added energy by direct absorption of electromagnetic energy; because this process is not driven by a temperature difference, heat was not involved at al!! We commonly measure temperature by means of a thermometer — a device that employs some material possessing a property that varies in direct proportion to the temperature.
The most common of these properties are the density of a liquid, the thermal expansion of a metal, or the electrical resistance of a material. The ordinary thermometer we usually think of employs a reservoir of liquid whose thermal expansion decrease in density causes it to rise in a capillary tube. Metallic mercury has traditionally been used for this purpose, as has an alcohol usually isopropyl containing a red dye.
Mercury was the standard thermometric liquid of choice for more than years, but its use for this purpose has been gradually phased out owing to its neurotoxicity. Although coal-burning, disposal of fluorescent lamps, incineration and battery disposal are major sources of mercury input to the environment, broken thermometers have long been known to release hundreds of tons of mercury.
Once spilled, tiny drops of the liquid metal tend to lodge in floor depressions and cracks where they can emit vapor for years. Temperature is a measure of the average kinetic energy of the molecules within the water. You can think of temperature as an expression of the "intensity" with which the thermal energy in a body manifests itself in terms of chaotic, microscopic molecular motion.
This animation depicts thermal translational motions of molecules in a gas. In liquids and solids, there is vary little empty space between molecules, and they mostly just bump against and jostle one another.
You will notice that we have sneaked the the word " translational " into this definition of temperature. Translation refers to a change in location: in this case, molecules moving around in random directions. This is the major form of thermal energy under ordinary conditions, but molecules can also undergo other kinds of motion, namely rotations and internal vibrations.
These latter two forms of thermal energy are not really "chaotic" and do not contribute to the temperature. Energy is measured in joules , and temperature in degrees. This difference reflects the important distinction between energy and temperature:. Temperature is measured by observing its effect on some temperature-dependent variable such as the volume of a liquid or the electrical resistance of a solid.
In order to express a temperature numerically, we need to define a scale which is marked off in uniform increments which we call degrees. The nature of this scale — its zero point and the magnitude of a degree, are completely arbitrary. Although rough means of estimating and comparing temperatures have been around since AD , the first mercury thermometer and temperature scale were introduced in Holland in by Gabriel Daniel Fahrenheit.
Fahrenheit established three fixed points on his thermometer. Zero degrees was the temperature of an ice, water, and salt mixture, which was about the coldest temperature that could be reproduced in a laboratory of the time. When he omitted salt from the slurry, he reached his second fixed point when the water-ice combination stabilized at "the thirty-second degree. Normal human body temperature registered Belize and the U.
In , the Swedish astronomer Anders Celsius devised the aptly-named centigrade scale that places exactly degrees between the two reference points defined by the freezing- and boiling points of water.
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