Conservation of Energy: The total amount of energy in a system remains constant ("is conserved"), although energy within the system can be changed from one form to another or transferred from one object to another. Energy cannot be created or destroyed, but it can be transformed.
Energy • Energy comes from the sun in the form of insolation. • Insolation is INcoming SOLar radiATION
Conduction Convection Radiation They may occur individually, or all three may occur at once. That energy is transferred by:
Lets start with conduction • In conduction, energy is transferred between substances by contact. • Energy is transferred from high to low. Therefore, when areas of higher temperature come into physical contact with areas of lower temperature, heat energy will be transferred. The hot object will cool down and the cool object will heat up until equilibrium is reached. • However; (there’s always a catch . . .) More heat is released from the warmer object than is gained by the cooler object. – some heat energy escapes into the surroundings during the process . . .
Examples of conduction: On a cold day, warm air inside the house comes in contact will cool air outside and escapes from the house ~ that’s why we need insulation! If an object is held in a flame (heat energy); the heat from the flame will travel down the object.
In the atmosphere, heating by conduction is primarily important at the ground, where air warms by directly contacting the surface. Sunlight has very little warming effect directly on air molecules.
Key Terms • Rate of Change: Change in field value over time; i.e. ~ how much has changed over how much time. • For example; If the temperature is 75o at 5:00 pm and 50o at 10:00pm, what would be the rate of change? • 75o - 50o (Change in field value) 5 hours (time) • Rate of Change = 5o/Hour
A few more key terms. . . • Calorimeter: Object used for measuring heat. (Heat can be measured in ‘calories’, unrelated to dietetic calories.) A calorimeter can be a thermometer, or any object used to measure temperature. • Potential Energy: Stored energy; higher temps mean higher potential energy. • Kinetic Energy: Energy of motion; more/faster motion means higher kinetic energy. Potential energy and kinetic energy are interchangeable – items at rest (potential) can move, items in motion (kinetic) can stop. The rock contains potential energy; if it falls, it’s kinetic (and painful . . . )
Kinetic and Potential Energy in action via conduction: • The stored heat energy (potential energy) on the left is being transferred to the cooler area on the right; once the heat is in motion, it becomes kinetic energy.
Convection: The transfer of energy by circulation. Energy will circulate based on differences in density; generally speaking, the higher the temperature, the lower the density. Therefore; higher temps tend to rise and lower temps tend to sink Causing convective circulation Now, how about convection:
A few more key terms . . . • Fluid: A substance with moderate density that flows easily and assumes the shape of its container. • Earth’s Mantle: The portion of Earth between the crust and outer core.
Convection in liquids: Warm liquid (less dense) rises, cool liquid (more dense) sinks; the motion creates convection cells and/or currents. Convection in air: The air above the blacktop is heated by the warm blacktop, causing the air to rise. The rising air is replaced by cooler air from over the meadow.
Warm substances (lower density) will rise when placed into cold substances Cold substances (higher density) will sink when placed in warm substances. So, we can figure that . . . • Introducing heat causes density to decrease – thus air rises.
And, last, but not least . . .Radiation~ it’s all about the waves . . . • Radiation is the transfer of energy through space by waves.
Not all radiation is the same, we receive and transmit radiation in a variety of ways.
Absorption & Radiation of Energy • Waves come in many shapes and sizes depending on a myriad of factors. • To keep it simple, short waves come from the sun and are absorbed by the Earth. The Earth processes the radiation (insolation) and re-radiates it back out as long waves.
Absorption and radiation are dependent upon the type of surface the waves encounter. • Dark rough surfaces absorb more, therefore re-radiate more.
Whereas, light, smooth surfaces tend to reflect the waves and thus re-radiate much less.
Key Terms: • Absorption: To take in/retain energy waves without reflecting. • Black dirt, for example, will retain insolation like a sponge retains water.
But, there are two sides to everything. . . • Reflection: To throw or send back from a surface. • Water will reflect insolation like a mirror reflects an image.
Re-radiation: To emit or send off after absorbing. • The desert sand absorbs short-wave insolation all day, then re-radiates long waves back out.
Radiative Balance: incoming = outgoing • (insolation = re-radiation)
So . . . • The rate at which energy is absorbed by a surface is determined by its color and texture. • Dark, rough surfaces will absorb and re-radiate much more than light, smooth surfaces.
Heat Equator: An imaginary line around the Earth connecting the points of highest or lowest average temperature at each longitude – NOT the same as the geographical equator
Energy absorption is affected by several factors: Amount of insolation Hours/intensity of daylight Angle of insolation Latitude Location Latitude and proximity to water Energy Absorption and Temperature
Amount of insolation • The total number of hours of sunlight we receive affects our temperature. • More sunlight = higher temps. • The quality of daylight absorption is also affected by various atmospheric conditions (cloud cover, pollution, etc.)
Angle of Insolation • The tropic region, (between 23.5 degrees N and 23.5 degrees S) is the only zone on Earth that has direct insolation. • As we move away from the equator, the angle is reduced. • Therefore, the higher the angle, the more intense the insolation.
Location, location, location • Land and water absorb heat differently. • Water is a poor absorber and, therefore, a poor radiator of heat. • Land is an excellent absorber and, therefore, an excellent radiator of heat.
And here comes density . . . • Because air is cooler over water during the day, the air over water is more dense • BUT – in the evening, the air over the land is cooler, and, therefore, more dense. • Land heats up and releases heat quickly; water heats up slowly, but also releases heat slowly, thus regulating the land temps around it.
So . . . • Cities at the same latitude will receive equal insolation, BUT . . . • The temperature ranges of coastal cities will be much more moderate than those of continental cities because water will moderate the temperature of the coastal regions. • Without a large body of water nearby, continental cities will have dramatic temperature ranges.
So; Now we know . . .We transmit heat energy via: • Conduction: Transfer by contact • Convection: Transfer by circulation • Radiation: Transfer by waves
… and we know the factors that affect temperature • Angle of insolation • Duration of insolation • Location (coastal or continental)
Oh no, not moreLABS!!!!! Labs 7-2 and 7-3 Pages 265 - 271