PHY205H1F Summer Physics of Everyday Life Class 5: Temperature, Heat • Temperature • Heat • Specific Heat Capacity • Thermal Expansion • Thermal Expansion of Water and Ice • Conduction • Convection • Radiation • Newton’s Law of Cooling • Global Warming and Greenhouse Effect
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PHY205H1F Summer Physics of Everyday Life Class 5: Temperature, Heat Temperature Heat Specific Heat Capacity Thermal Expansion Thermal Expansion of Water.
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PHY205H1F Summer Physics of Everyday Life
Class 5: Temperature, Heat
• Temperature• Heat• Specific Heat Capacity• Thermal Expansion• Thermal Expansion of
Water and Ice
• Conduction• Convection• Radiation• Newton’s Law of
Cooling• Global Warming and
Greenhouse Effect
• It’s one of the first things we think about in the morning: What’s the temperature like outside?
Temperature
• We can measure temperature with a• Temperature has something to do with
of the atoms in a material
• A cold cup of coffee has a low amount of
• If you put it in the microwave, the microwave radiation transfers energy to the coffee, increasing its
, which increases its temperature.
Temperature
• Gas—how fast the gas particles are bouncing around
• Liquid—how fast particles slide and jiggle past one another
• Solid—how fast particles move as they vibrate and jiggle in place
Absolute temperature (in degrees Kelvin) is proportional to the average translational per particle in a substance.
[animated gif downloaded Jan.25 2013 from http://www.deanza.edu/faculty/mccauley/6a_site_images/Translational_motion-250.gif ]
The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water
A. decreases more.
B. increases more.
C. does not change.
D. Not enough information.
Quantity of HeatCHECK YOUR NEIGHBOR
You heat a half-cup of tea and its temperature rises by 4C. How much will the temperature rise if you add the same amount of heat to a full cup of tea?
Thermal expansion Different substances expand at different rates.Example:
• When the temperature of a bimetallic strip of and is increased, greater expansion
occurs for the strip, which bends to turn a pointer, to regulate a valve, or to close a switch.
Bimetallic strips are used in heaters, oven thermometers, refrigerators, and electric toasters.
Thermal Expansion• The metal in a metal ring expands.• So the ring will get thicker and longer – more
circumference, so larger.• All linear dimensions of an object expand if the
temperature : outer diameter, and inner diameter of ring.
• Also the inner diameter of a metal jar lid when it is heated!
Expansion of water to ice• When water becomes ice, it ! Ice has
open-structured crystals resulting from strong bonds at certain angles that increase its volume. This make ice than water.
Thermal Expansion: The exception to the rule
When a sample of 0C water is heated, it first
A. expands.
B. contracts.
C. remains unchanged.
D. Not enough information.
Thermal ExpansionCHECK YOUR NEIGHBOR
Conduction
• Transfer of by electron and molecular collisions within a substance, especially a solid
If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand?
A. Yes
B. In some cases, yes
C. No
D. In some cases, no
ConductionCHECK YOUR NEIGHBOR
Insulation• Doesn’t prevent the flow of internal energy• the rate at which internal energy flows
Example: Rock wool or fiberglass between walls slows the transfer of internal energy from a warm house to a cool exterior in winter, and the reverse in summer.
[image downloaded Feb.1 2013 from http://owenscorning.eu/en/products/residential-insulation/pink044.aspx ]
Cooling by • Opposite to the warming that occurs when air is
compressed
Example: The “cloudy” region above hot steam issuing from the nozzle of a pressure cooker is cool to the touch (a combination of air expansion and mixing with cooler surrounding air).
Careful, the part at the nozzle that you can’t see is steam—ouch!
Gas Cooling By Expansion
• Molecules in a region of expanding gas collide more often with receding molecules than with approaching ones
• Their rebound speeds therefore tend to decrease, and, as a result, the expanding gas cools.
• This phenomenon is used in , which use cooled coils to remove heat from a low temperature environment
Radiation
• Transfer of energy via such as light or infrared.
The surface of Earth loses energy to outer space due mostly to
A. conduction.
B. convection.
C. radiation.
D. radioactivity.
RadiationCHECK YOUR NEIGHBOR
Radiation• Transferred energy• Exists as electromagnetic waves ranging from
long (radio waves) to short wavelengths (X-rays)• In region, ranges from long
When to add cream to coffee…• Psy likes to drink his coffee hot, and he likes cream in his
coffee. He buys it at Starbucks but does not want to drink it until he gets to his home, which is a 5 minute walk. To keep the coffee as hot as possible, should he add the cream at Starbucks or at home?
A. Starbucks, before the 5-minute walk
B. At home, just before drinking
C. It doesn’t matter
When to add cream to coffee…• My reasoning:• When you add the cream to the coffee, it is going to
decrease its temperature by some amount; this is about the same whether you do it at home or at Starbucks.
• When you carry the coffee through the environment for 5 minutes, it will be losing heat, since the coffee temperature is higher than the environment.
• The rate of heat loss over this 5 minutes is proportional to
• If you added the cream first, is less while you carry it, so it is going to lose heat en route.
• In the end, this leads to coffee when you eventually drink it.
It is commonly thought that a can of beverage will cool faster in the coldest part of a refrigerator. Knowledge of Newton’s law of cooling
A. supports this knowledge.
B. shows this knowledge is false.
C. may or may not support this knowledge.
D. may or may not contradict this knowledge.
Newton’s Law of CoolingCHECK YOUR NEIGHBOR
Greenhouse effect• Named for a similar effect
in florists’ greenhouses
Greenhouse Gases• The Earth’s atmosphere contains mostly
Nitrogen and Oxygen, both of which are (non-absorbing) of both visible and
infrared radiation• Certain gases are for visible
radiation, but for infrared radiation
• These are called “ ”:– Carbon Dioxide– Water vapour– Methane– Nitrous oxide
[image from http://en.wikipedia.org/wiki/File:Exhaust_pipe_muffler.JPG ]