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Ch. 9 Section 2

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Tsai Chi Shang Kuan

on 15 February 2013

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Transcript of Ch. 9 Section 2

Chapter 9 Section 2 Defining Heat On a Microscopic Level Heat VS Temperature Archer, Maria, Cathy Temperature Temperature is a measure of the average kinetic energy of particles
All objects have some internal energy so all objects have some temperature On a Macroscopic Level Heat travels spontaneously from hotter objects to cooler ones until both final temperatures are the same What is Heat? The energy transferred between objects that are at different temperatures. A warmer object has a higher average kinetic energy than a cooler object.
The energy from faster-moving molecules is transferred to the molecules of a cooler object through vibration and collision
Thermal equilibrium is reached when all the particles have, on the average, equal kinetic energies IMPORTANT!
At this level, energy can be transferred in either direction (from lower-energy molecules to those with higher-energies or the opposite).
The net transfer of energy as heat is, however, in the direction of objects with lower-energies. When there is no temperature difference, no net energy is transferred as heat
The greater the temperature difference, the greater the rate of energy transfer between them as heat
The transfer of energy as heat alters an object’s temperature Thermal Conduction Thermal Conduction is the transfer of energy between neighboring molecules
The rate of thermal conduction depends on the properties of the substance being heated. -Substances that rapidly transfer energy as heat are called thermal conductors.
-Substances that slowly transfer energy as heat are called thermal insulators. Two other mechanisms for
transferring energy between
places or objects at different
Electromagnetic radiation doesn’t involve the transfer of matter. It is a form of energy emitted and absorbed by charged particles which exhibits wave-like behavior as it travels through space. Heat and Work Friction is one way to increase a substance’s internal energy.
For solid substances, internal energy can be increased by deforming their structure.
Ex. Stretching a rubber band or bending a metal. Total energy is conserved, where the sum of the changes in potential, kinetic, and internal energy is equal to zero. Conservation of Energy: ΔPE + ΔKE + ΔU = 0 Units of Heat Heat is represented with the symbol Q
Heat is a form of energy, like work, so the SI unit of heat is Joules (J)
Another unit of heat is calorie (cal) which is equal to 4.186 J
Calorie, on the other hand, is equal to 1000 calorie Ex. Metal ice tray vs. a plastic package of frozen food removed from the freezer at the same temperature, the metal tray feels colder because metal conducts energy more easily and more rapidly. Convection involves the movement of cold and hot matter such as hot air rising upward over a flame (doesn’t involve heat alone; but involves effects of pressure differences, conduction, and buoyancy). Sample Problem B Joule's Apparatus with 11.5 kg mass and 1.3m height
What is ΔU?
ΔPE + ΔKE + ΔU = 0
(PE,f - PE,i) + (KE,f + KE,i) + ΔU = 0
ΔU = PE,i - PE,f + KE,i - KE,f
ΔU = mgh - 0 + 0 - 0
ΔU = (11.5 kg)(9.81 m/s^2 )
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