Thermal Energy and Matter
Heat is the transfer of thermal energy from one object to another as a result of a difference in temperature. The picture shows the sun, which transfers its energy to Earth because the sun and Earth have different temperatures. Thermal energy is the total potential and kinetic energy of all the particles in an object. It depends on mass, temperature, and phase (solid, liquid, or gas). Temperature is defined as a measure of how hot or cold an object is compared to a reference point. Matter is something that takes up space and possesses rest mass. When thermal expansion happens, it is because the particles of matter tend to move farther apart as temperature increases. But when the particles move closer together as temperaure increases, it is called thermal contraction. The picture below is an example of how two objects can have the same temperature but different thermal energies.
Specific Heat
The amount of heat needed to raise the temperature of one gram of material by one degree Celsius (0 being the freezing point and boilng point is 100) is called specific heat. The reason why you are more likely to burn yourself on a metal toy than a plastic toy is because the metal has a lower specific heat which allows the metal toy to get hotter faster than the plastic toy. The formula for specific heat is Q=m*c*T. Q is the heat, m is the mass, c is the specific heat, and T is the change in temperature.
Measuring Heat Changes
An instrument used to measure changes in thermal energy is a calorimeter. It uses the principle that heat flows from a hotter object to a colder one until both objects reach the same temperature. The picture to the left is an example of a calorimeter.
Heat and Thermodynamics
Conduction and Convection
Conduction is the transfer of thermal energy with no overall transfer of matter. Conduction tends to be slower in gases than in liquids or solids because the particles in gases collide less often. Newton's cradle is one of the many examples of conduction. Convection is the transfer of thermal energy when particles of a fluid move from one place to another. When you are heating up a pot of water, the handle gets hotter, which is conduction. The convection is the water inside of the pot. Conduction is faster in solids than liquids or gases because the particles collide more often in solids than the other two. The reason metal heats up faster is because metal is a solid and has a lower specific heat. A thermal conductor is a material that conducts thermal energy well and a thermal insulator conducts thermal energy poorly. An example of a thermal conductor could be a frying pan. An example of a thermal insulator would be air or a window pane because the window is designed to help keep air out or away.
Radiation
Radiation is the transfer of energy by waves moving through space. An example of radiation could be heating coils on a stove or the sun. The sun's rays travel through space to get to Earth and transfers its energy to heat Earth up. All objects radiate energy. Whether it is a light or a toy sitting in the sunlight. As an object's temperature increases, the rate at which it radiates energy increases. The temperature is higher at the bottom of an oven than any other part. The reason why is because the heat is coming from the bottom of the oven which is going to cause the bottom to be hotter than the rest of the oven.
Thermodynamics
The study of conversions between thermal energy and other forms of energy is called Thermodynamics. The first law of Thermodynamics states that energy is conserved. If energy is added to a system, it can either increase the thermal energy of the system or do work on the system. The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system. An example of the second law would be, a refrigerator, because it must transfer energy to the warm object to make the object colder and to keep it cold inside the refrigerator because of the warm air outside of it.