Question

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u4l4 - direction of heat transfer homework
team:
part 1:
read the textbook section below to extend your understanding of the concepts from this week
show your strong annotations and marginal notes!
7.4 heat transfer
thermal energy flows from a material at a higher temperature to a material at a lower temperature.
this process is called heat transfer. how is heat transferred from material to material, or from place
to place? it turns out there are three ways heat flows. in this section, you will learn about heat
conduction, convection, and thermal radiation.
heat conduction
what is conduction? heat conduction is the transfer of heat by the direct contact of particles of
matter. if you have ever held a warm mug of hot cocoa, you have experienced
conduction. heat is transferred from the mug to your hand. conduction only
occurs between two materials at different temperatures and when they are
touching each other. in conduction, heat can also be transferred through
materials. if you stir hot cocoa with a metal spoon, heat is transferred from the
cocoa, through the spoon, and to your hand.
conduction is the transfer of heat by the direct
contact of particles of matter.
how does conduction work? imagine placing a cold spoon into a mug of hot cocoa (figure 7.16). the
molecules in the cocoa have a higher average kinetic energy than those of the
spoon. the molecules in the spoon exchange energy with the molecules in the
cocoa through collisions. the molecules within the spoon itself spread the
energy up the stem of the spoon through the intermolecular forces between
them. conduction works through both collisions and also through
intermolecular forces between molecules.
thermal equilibrium as collisions continue, the molecules of the hotter material (the cocoa) lose
energy and the molecules of the cooler material (the spoon) gain energy. the
kinetic energy of the hotter material is transferred, one collision at a time, to
the cooler material. eventually, both materials are at the same temperature.
when this happens, they are in thermal equilibrium. thermal equilibrium
occurs when two bodies have the same temperature. no heat flows in thermal
equilibrium because the temperatures are the same.
vocabulary
heat conduction, thermal conductor,
thermal insulator, convection,
thermal radiation
objectives

• explain the three methods of

heat transfer and name
examples of each

• give examples of thermal

conductors and thermal
insulators

• describe the direction of heat

transfer between two objects
figure 7.16: heat flows by conduction
from the hot cocoa into and up the spoon.

1. explain the process of heat conduction using evidence from the text.

1. what information do you need to know about two objects that are in contact in order to

determine the direction of energy flow?

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Explanation:

Question 1

To explain heat conduction, we use the text's definitions and examples. Heat conduction is heat transfer via direct particle contact (from the text: "Heat conduction is the transfer of heat by the direct contact of particles of matter"). The hot cocoa - spoon example shows this: cocoa molecules (higher kinetic energy) collide with spoon molecules. Collisions and intermolecular forces transfer energy up the spoon (as stated: "Conduction works through both collisions and also through intermolecular forces between molecules"). Eventually, if contact continues, thermal equilibrium is reached (when temperatures are equal, no heat flows).

The text says "Thermal energy flows from a material at a higher temperature to a material at a lower temperature". So to determine energy flow direction between two contact objects, we need their temperatures. If we know the temperature of each object, we can tell that energy flows from the higher - temperature object to the lower - temperature one.

Answer:

Heat conduction is the transfer of heat by direct contact of matter particles. For example, when a cold spoon is placed in hot cocoa, cocoa molecules (with higher average kinetic energy) collide with spoon molecules. Through collisions and intermolecular forces, energy is transferred up the spoon. As collisions continue, the hotter material (cocoa) loses energy and the cooler material (spoon) gains energy. Eventually, if contact persists, thermal equilibrium is reached (same temperature, no heat flow), as defined in the text.

Question 2