Heat The Fire Down Below

Heat A flow of energy from objects of higher thermal energy to objects of lower thermal energy Heat is measured in Joules (J) because it is a form of energy Described as a flow from hot to cold No such thing as “cold”

Temperature Based on the motion of the particles in a substance Fast motion = high temperature Slower motion = lower temperature Relatively describes how the particles collide with the surface of the thermometer Collisions transfer energy

Temperature Scales Fahrenheit Common in the US Freezing point of water is 32ºF Boiling point of water is 212ºF Celsius Common in the rest of the world (SI) Freezing point of water is 0ºC Boiling point of water is 100ºC

Temperature Scales Kelvin Used for science, as there are NO negative values 0K is set at Absolute Zero, the temperature at which all particle motion stops Freezing point of water is 273K Boiling point of water is 373K NOTE – 100K between freezing and boiling, so Kelvin uses the same degrees as Celsius

Converting Temperatures Fahrenheit to Celsius Cº = 0.55 (Fº - 32º) Celsius to Fahrenheit Fº = (1.8 x Cº) + 32º Celsius to Kelvin K = C Adjusts for differences in Zero temperature

Because heat is a form of energy, heat is measured in … 1.Watts 2.Newtons 3.Joules 4.Mishbohah

Heat always flows… 1.From low E to high E 2.From high E to low E 3.Across layers of density 4.Downwards, like gravity

The average motion of particles in a substance defines that substance’s… 1.Heat 2.Energy 3.Potential Energy 4.Temperature

The temperature scale used in the USA is 1.Fahrenheit 2.Celsius 3.Kelvin 4.Thermocline

The temperature scale used in SI is 1.Fahrenheit 2.Celsius 3.Kelvin 4.Thermocline

The temperature scale used in science is 1.Fahrenheit 2.Celsius 3.Kelvin 4.Thermocline

Thermal Energy Usually based on the total number of particles, as most temperatures in which we survive are relatively close together (-15ºF to 130ºF) More particles = more thermal energy Ex. boiling cabbage, frying foods, ocean water

Heat Transfer Conduction HTB direct particle contact Convection HTB mass movement of particles Radiation HTB invisible infrared radiation

Conduction Heat transfer by direct particle contact The particles of the higher energy material vibrate more rapidly As they collide with the lower energy material, some of the particles increase speed Eventually, all the particles vibrate at the same speed Mix hotter and colder materials? The temperature moderates…

More on conduction…

Convection Heat transfer by mass particle movement The particles of the higher energy material vibrate more rapidly, and Thermal expansion causes the particles of the hotter material to become less dense The warmer, less dense material rises, The cooler, more dense material sinks

Above and Below… Inside the Earth, heat from Earth’s core moves towards the surface through the plastic mantle

Above and Below… The atmosphere and hydrosphere move heat through convection in weather and ocean currents

Radiation Heat transfer by invisible, electromagnetic waves Infrared waves are given off because of particle motion or electrons changing energy levels during reactions The waves released can be absorbed by other particles, interpreted as heat

Feel the heat! The Earth is warmed by infrared radiation from the Sun NO HEAT IS RECEIVED FROM THE SUN BY DIRECT PARTICLE CONTACT

What type of heat transfer describes cooking on an electric range? 1.Conduction 2.Convection 3.Radiation

What type of heat transfer describes why a dark shirt feels warmer on sunny days? 1.Conduction 2.Convection 3.Radiation

What type of heat transfer describes how a A/C system changes room temperature? 1.Conduction 2.Convection 3.Radiation

What type of heat transfer describes how lake water is hot on top and cold on bottom? 1.Conduction 2.Convection 3.Radiation

What type of heat transfer describes cooking in an electric oven? 1.Conduction 2.Convection 3.Radiation

Thermos bottles… Reduce heat flow in BOTH directions Vacuum eliminates convection, conduction Inner bottle is usually reflective to reduce radiation

Specific Heat Amount of energy that has to be lost or gained by a substance to change temperature Note: Water has an incredibly high specific heat value due to the bonds between water molecules Ammonia has a higher specific heat, but you can’t use it to cook!

Specific Heat Q = m c  T where m is the mass of the substance c is the specific heat value  T is the change in temperature of the substance (T final – T initial )

More on Radiation Emitters are substances that give off radiation Stars, campfires, space heaters, etc. Absorbers capture radiation Black shirts, asphalt, water Reflectors return most of the radiation that is emitted towards them Mirrors, aluminum foil, ice & snow

Thermal Expansion As substances increase in temperature, the particles move apart Essentially Charles’s Law: As temperature increases, volume increases As temperature decreases, volume decreases Substances expand and become less dense when heated Substances shrink and become more dense when cooled

Thermal Expansion Explains expansion joints in bridges and concrete sidewalks Water is one very important exception As liquid water freezes to become ice, the water molecules arrange in to a lattice with air spaces ICE FLOATS BECAUSE IT IS LESS DENSE Density of liquid water = 1g/cm 3 Density of ice = 0.92 g/cm 3

Examples of Thermal Expansion Notice the cracks that have formed in the concrete after some time of thermal expansion

Conductors Allows heat (and electricity) to flow easily with little or no resistance Heats up quickly, cools down quickly Low “Specific Heat” Usually metals High density (no air spaces), free electrons

Insulators Resist the flow of heat (and electricity) High “Specific Heat” Designed to trap “dead air” spaces Resisted heat can build up and cause the substance to burn Usually nonmetals Large molecules, no free electrons

Layers and Heat Transfer Layers trap air in a “dead air space” More layers mean it’s harder to change temperatures between layers Ex. double-paned windows, dressing in layers, layers of construction on a house

Combining insulation Notice the pipes wrapped in “fluffy” insulation, but the outside is shiny. The “fluffy” traps “dead air” spaces where the shiny inhibits radiation

Why are gaps designed in bridges, roads and sidewalks? 1.As temperatures drop, the materials contract 2.As temperatures rise, the materials expand 3.To save money on the project by reducing the amount of materials 4.None of the above

Which type of heat transfer is impeded by reflective materials ? 1.Convection 2.Conduction 3.Radiation 4.None of the above

Which type of window would be the best insulator for your home? 1.Single-paned 2.Double-paned 3.Triple-paned 4.Wooden shutters

Which type of heat transfer is impeded by materials that trap “dead air” spaces ? 1.Convection 2.Conduction 3.Radiation 4.None of the above

Which type of heat transfer is impeded by vacuums and gaps in designs ? 1.Convection 2.Conduction 3.Radiation 4.None of the above

Explain these… Why was the Amundsen- Scott Antarctic Station is built to be half under the ice? Why do desert-dwelling peoples wear a dark outer layer on top of their inner layers?

Explain these… Why would a hunter “dress in layers” the way your parents always suggest? What can you infer about the parts of the roof of this house that have no snow?