Conceptual Physics Alive: Heat
Paul Hewitt teaches about Heat Temperature & Expansion, Heat Transfer, Heat Radiation and Heat: Changes of State.
Master teacher Paul Hewitt teaches Conceptual Physics. Observe Hewitt teach in a classroom with real students, using engaging demonstrations and artwork.
DVD Includes 4 Episodes:
- Episode 1: Heat, Temperature, and Expansion: Temperature and heat are distinguished from each other. The expansion of solids, liquids, and gases is compared. A discussion on specific heat capacity leads to the physics of a freezing lake. Demonstrations using liquid nitrogen show the effects of low temperatures. Segment length: 44 minutes
- Episode 2: Heat Transfer: Conduction is related to many everyday examples and is demonstrated by boiling water under a variety of conditions. Convection is shown with a pressure cooker. Radiation is related to Newton's law of cooling. Segment length: 45 minutes
- Episode 3: Heat Radiation: The temperature dependence of radiation frequencies are related to the greenhouse effect. The way in which sunlight spreads differently over parts of the earth helps explain the warmth of the equatorial regions and coolness of polar regions. Segment length: 32 minutes
- Episode 4: Heat: Change of State: The concepts of evaporation and condensation are contrasted. The energy transfer that accompanies changes of state is related to everyday examples. Segment length: 46 minutes
Heat, Temperature, and Expansion includes:
• Hewitt begins by comparing internal energy and temperature.
• Thermometer construction discussed.
• Celsius and Fahrenheit scales compared.
• High temperature but low internal energy 4th-of-July-type sparklers.
• Specific heat capacity.
• Water's high specific heat, with examples.
• Aluminum's low specific heat.
• Specific heat of foods.
• Example of water's high specific heat: Hot water bottle during Hewitt's childhood on cold Boston winter nights.
• Global heating via water's high specific heat.
• Expansion of water upon freezing.
• Six sided crystal structure of snowflakes.
• Why ice is less dense than water.
• Expansion of water when heated.
• Graphical explanation of the low density of water at 4°C.
• No ice on deep lakes in the cold winter.
• Why ice forms at the surface of a lake in cold weather (with class questions).
• Demonstration of liquid nitrogen with assistant Ted Brattstrom; balloon volume change; flower going brittle when cooled; cooling cracker and putting in mouth.
Next-Time Question: When a metal ring is heated, will its inner diameter become larger, smaller, or stay the same? [It will become larger, for all parts including the inner circumference expand].
Heat Transfer includes:
• Hewitt begins by heating a metal ring with a torch to see the effect on hole size. The hole gets larger, which answers the homework (Next-Time Question) of the previous lecture.
• Chalkboard explanation is given of the increase in hole size.
• Demonstration of heating a bimetallic strip. Its application is the thermostat.
• The wooden handle of the bimetallic strip and poor heat conduction.
• Conductors and the presence of loose electrons about atomic nuclei.
• Wood is a poor conductor at any temperature, whether in a hot oven or as red-hot coals.
• Walking barefoot on red hot coals without harm is explained.
• Conductivity of chairs in classroom compared by students.
• Demonstration of wrapped paper around a piece of iron in a hot flame.
• Why the paper doesn't light on fire.
• Demonstration repeated with paper wrapped around wood.
• Demonstration of water in a paper cup held in the flame.
• Demonstration of poor heat conductivity of water. An ice cube wedged at the bottom of a test tube filled with water is held in a flame, to show that the water at the top of the tube boils while the ice cube remains intact.
• Water's poor conductivity and the constant 4C water that remains at the bottom of deep lakes that have high temperature surfaces.
• Poor conductivity of air, with examples of down filled sleeping bags, the fur of animals, Styrofoam, spun glass, and thermal underwear.
• Convection, and why warm air rises.
• Helium atoms and their rise in the atmosphere.
• The expansion of rising warm air and cooling.
• Student demonstration of cooling by blowing on hands.
• Demonstration of hand in the path of expanding steam from a pressure cooker.
• Explanation of why air cools when it expands.
• Frequency and temperature relations or radiation.
• Wave motion simulated by shaking an imaginary rubber tube.
• The green house effect and its explanation.
Heat Radiation includes:
• Review of heat transfer by radiation.
• Radiant energy: Everything is emitting: everything is absorbing.
• Hewitt shows a wooden box with a hole in it. The hole looks black, while the interior is white.
• Blackness of eye pupils.
• Twice-as-hot coffee story to illustrate the concept of absolute zero.
• Review of the Fahrenheit and Celsius temperature scales.
• Introduction of the Kelvin scale.
• The "Celsius-the-Village-Tailor" story.
• Newton's law of cooling; Rate of cooling- delta T.
• Example of a house ' leaking" heat energy.
• Example of delta T and frogs.
• Example of delta T and people.
• The physics of cooking lobsters and crabs.
• Warmness of tropics and coolness of Arctic.
• The earth's tilt and seasons.
• Arctic Circle.
• Shortness of nights in brother's farm in Costa Rica.
• Hewitt holds two sheets of paper in an imaginary rain to show how their different angles are analogous to the angle of sunlight on earth that produces seasons.
Heat: Change of State includes:
• Evaporation is introduced with skit about massaging with alcohol.
• Graph of molecules versus relative numbers of molecules in a container of water.
• Evaporation and molecular speed.
• Example of evaporation: Indian child keeping a jug of water cool.
• Examples of cooling by evaporation: dogs panting, pigs wallowing in the mud, people perspiring.
• Hewitt's experience in a hot tub where evaporation was prevented and overheating of the body, rather than cooling, occurred.
• Boiling and cooling.
• Hewitt shows a pressure cooker and explains how boiling and therefore cooling is prevented via a chalkboard diagram.
• Hewitt tells of the exhibit at the Exploratorium In San Francisco that freezes water by boiling in a vacuum.
• The physics of cooking spaghetti.
• Low-temperature boiling at high altitude.
• Condensation, the opposite of evaporation, and a warming process.
• Remaining in a shower and muggy days.
• How air warms when condensation occurs.
• Energy changes with change of state.
• Why water in a farmer's canning cellar doesn't freeze m subzero temperatures.
• Why a steam burn is more damaging than a boiling water burn.
• How air conditioners work by change of phase.
• Condensation examples: shapes of drinking glasses, napkins beneath cold drinks, water rings from ice-cold drinks on a surface, the moisture inside a parked car, clouds in the sky. Hewitt humorously relates all these to CH (Condensation Honey!)
• Why clouds form over mountains.
• Why clouds form over Islands with no mountains.
• Cooling of expanding air, and warming by compression.
• Cooling of rising air by 10 degrees for every 1 km increase in elevation.
Next-Time Question: If a baggie of air 5 km high at 0 degrees C is quickly pulled down to the ground, what will its temperature be? (With no heat transfer, the temperature will be -50C because it loses 10 degrees C for every 1 km decrease in elevation.)