6.2 H

EAT p. 275-280



H EAT Heat

is the energy transferred from a warmer object to a cooler object.

 Heating involves energy transfer on the microscopic level.

Heat When two substances of different temperatures are in thermal contact, heat flows from the higher-temperature substance into the lower temperature substance.

Heat

 If you touch a hot stove, energy enters your hand from the stove because the stove is warmer than your hand.  hand into the colder ice.  transfer is always from a warmer to a cooler substance.  If you touch ice, energy passes from your The direction of spontaneous energy

The energy that transfers from one object to another because of a temperature difference between them is called heat.

Heat

   It is common—but incorrect with physics types—to think that matter contains heat. Matter contains energy but it does not contain heat. Heat is energy in transit, moving from a body of higher temperature to one of lower temperature.

Heat

   Once transferred, the energy ceases (stops) to be heat.

we called the energy resulting from heat flow thermal energy, to make clear its link to heat and temperature

(aside: the term that scientists prefer is internal energy.)

When heat flows from one object or substance to another it is in contact with, the objects are said to be in

thermal contact.

 a) two iron nails with same temperature and same mass have the same amount of

thermal energy

 Two iron nails with the

same temperatures but

different masses; the nail with more mass has more thermal energy because has more vibrating iron atoms

T HERMAL E NERGY T RANSFERS

 Thermal energy can be transferred from one place to another by conduction,

convection, and/or

radiation.  Often, transfer of thermal energy occurs through two or even all three processes simultaneously .

(1) C ONDUCTION



Conduction

is the transfer of thermal energy through direct contact between

the particles of two substances, without the particles moving to a new location.

 The energetic particles of the warmer material collide with the less energetic particles of the cooler material.  The slower particles gain energy and collide with other particles in the cooler object.

 

thermal equilibrium

when two objects are at the same temperature. - the point Here, the objects stop exchanging energy.

 Since the particles in solids are closer together, solids conduct thermal energy better than liquids, and liquids conduct thermal energy better than gases.  Good conductors of electricity, such as metals, are often good conductors of thermal energy.

(2) C ONVECTION



Convection

is the transfer of thermal energy through the

bulk movement of particles

from one location to another.  Convection occurs in fluids (liquids and gases), where the particles have freedom of movement and are not locked in place as they are in a solid.



Convection

flows down.

is a natural stirring of a fluid: hotter, less dense material flows up while cooler, denser material

 Eventually, all the material is heated to a uniform temperature.



In liquids and gases, convection is usually the most efficient way to transfer thermal energy.

(3) R ADIATION



Radiation

particles. is the transfer of energy as electromagnetic waves or fast-moving  The energy transferred in these waves or particles is called

radiant energy .



You can feel warmth even though there

is no contact.

 Radiation carries energy through empty space. 

When radiant energy reaches an object, it is transferred to the object’s particles as kinetic energy, and the temperature of the material rises



The most common types of radiant energy are

visible light and other sorts of electromagnetic radiation, such as infrared and ultraviolet radiation.

H OMEWORK

6.2

 P. 280 questions #1-5