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by: HaleyG

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# PHYS 1010 - Week 6 Notes PHYS 1010-01

Marketplace > Tulane University > Physics 2 > PHYS 1010-01 > PHYS 1010 Week 6 Notes
HaleyG
Tulane
GPA 3.6

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Lecture notes
COURSE
Great Ideas in Science & Tech
PROF.
Timothy Schuler
TYPE
Class Notes
PAGES
3
WORDS
CONCEPTS
Schuler, Physics
KARMA
25 ?

## Popular in Physics 2

This 3 page Class Notes was uploaded by HaleyG on Friday February 19, 2016. The Class Notes belongs to PHYS 1010-01 at Tulane University taught by Timothy Schuler in Fall 2016. Since its upload, it has received 24 views. For similar materials see Great Ideas in Science & Tech in Physics 2 at Tulane University.

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Date Created: 02/19/16
PHYS 1010 Notes Week 6 Feb 15­19 Thermal energy ­ Based on experiments with friction ­ Two surfaces moving in contact with one another get hotter ­ Motion causes heat ­ Kinetic energy can be turned into heat and vice versa ­ Heat: change in temperature that occurs when thermal energy is transferred  between two objects in contact ­ Heat is thermal energy (internal energy), which is a form of physical  energy ­ Heat is positive when energy is transferred to an object's thermal energy  from the environment, and negative when the object loses thermal energy to its  environment ­ Heat is always transferred from the hotter object to the colder object ­ Heat is related to random kinetic energy of particles within a substance ­ Bigger vibrations means more thermal energy ­ Thermal expansion: adding kinetic energy to a solid lattice causes atomic bonds to stretch and leads to an expanding of the entire lattice ­ Thermal expansion is the way we measure temperature ­ Overstretching ­­> turns from solid to liquid to gas ­ Transfer of heat ­ Radiation: heat from light ­ Conduction: heat transferred because a hotter object is touching a cooler  object ­ Convection: heat transfer by motion of fluid (air or water) when the  heated fluid moves away from the object, carrying heat with it ­ Absorption of heat ­ Heat capacity: tells us how much energy will be required to heat up an  object ­ Larger heat capacity means a larger temperature change for the  same amount of energy; heat capacity is different for different substances ­ Specific heat: heat capacity per unit mass of a substance ­ More mass means more energy is required to change the  temperature of the object ­ Metal conducts heat very well; insulating materials like fiberglass and Styrofoam trap air and hold it in place to keep things cool ­ Air almost doesn't conduct heat Temperature: used to describe a measure of heat ­ SI unit: Kelvin ­ Lowest possible limit: 0 K (when atoms stop vibrating); no upper limit ­ Matter can't exist below 0 K ­ Celsius scale is defined in relation to Kelvin scale ­ Fahrenheit scale is defined in terms of Celsius scale Work done on a system by an external force ­ External forces can do work on a closed system by transferring energy to or  from a system ­ Work done against friction (force times distance) becomes thermal energy (heat) ­ Work done against the force of friction is the loss of mechanical energy  to thermal energy Conservation of Energy ­ The total amount of energy in a closed system can never change  ­ Energy may change forms but sum of all forms stay constant ­ Earth is not a closed system ­ Sun gives constant new energy ­ Universe is a closed system Laws of Thermodynamics ­ 0th Law: if objects A and B are each in thermal equilibrium with a third object  C, then objects A and B are in thermal equilibrium with each other ­ If something is in one part of a system, then it is in all parts of the system ­ 2nd Law: the entropy of a closed system can never decrease ­ 1st Law: the difference between the transferred thermal energy and change in  mechanical energy determines the change in the internal energy of the system ­ 3rd Law: in order to cool something to 0K, you need something colder than 0K,  which can't exist as matter. Therefore nothing can be cooled to 0K. Entropy: randomness/disorder ­ Many processes that occur in nature are irreversible (not symmetric) ­ Problematic because conservation of energy is symmetric and doesn't  suggest any kind of direction ­ The entropy of a system, which is not conserved, sets the direction of  irreversible processes ­ If an irreversible process occurs in a closed system, the amount of  entropy always increases (it can never decrease) ­ Change in entropy is thought to be a factor in our concept of the "arrow of time" ­ Time moving backwards would violate the concept of entropy Heat engines and refrigeration ­ Thermal energy can be turned into work (mechanical energy) ­ Put hot object in contact with a cold object ­­> thermal energy moves from hot  object to cold object ­ Then, we can siphon off the energy that's moving between the objects and use it  to drive the engine ­ Q Hot Q  Cold+ Work ­ Efficiency = (Q   Hot  Cold / Q Hot ­ The efficiency can never be 100% because some heat must flow to the cold  object; however, the energy being transferred to the cold object doesn't do us any good ­ Refrigerators go from hot to cold­ fridges are just reversing the previous flow of  energy. We need a heat engine as well as the cooling system ­ Can never be 100% efficient

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