Energy Transfer and the Solar System
Transferring Energy
How is Energy Transferred by Heating?
Energy can be transferred by heating through:
Evaporation
Radiation
Conduction
Convection
Radiation
Energy is transferred from hot objects via radiation, also known as infrared radiation.
All objects emit infrared radiation; the hotter the object, the more radiation emitted.
Radiation can be absorbed or reflected when it hits an object.
Infrared radiation transfers energy through waves, similar to light, and does not require a medium to travel.
It can travel through transparent substances like air or glass.
Infrared radiation can be focused, demonstrated by the Sun's energy burning paper through a magnifying glass.
Thermal imagers measure infrared radiation and convert it into temperature maps, useful for night filming.
Conduction
Energy transfer through solid materials via conduction involves particles vibrating more when heated.
These vibrations are passed through the solid.
Metals are good thermal conductors, while materials like wood and plastics are thermal insulators.
Conduction is most effective in solids due to the close proximity of particles.
Conduction is less effective in liquids and minimal in gases due to particle spacing.
Convection
Energy is transferred through fluids (liquids and gases) by convection.
When a fluid is heated, it expands, becomes less dense, and rises, creating a convection current.
Cooler fluid moves in to replace the rising warm fluid.
Convection currents also form when part of a fluid is colder than its surroundings.
Temperature maps using infrared measurements from satellites show convection currents in the air above oceans, which we feel as wind.
Controlling Energy Transfers
How Can We Control Energy Transfers?
Insulation helps keep warmth inside houses in cold climates, saving fuel.
Brick, wood, and other building materials are good insulators.
Air is a poor conductor but a good insulator when trapped, as in carpets, feathers, and wool.
Aerogel, over 99% air, is one of the best insulating materials and can be used in thin sheets.
Light colors and shiny surfaces reflect infrared radiation, helping to keep houses cool in hot countries.
Dark colors absorb and emit infrared radiation well, so solar panels are painted black.
Spraying elephants with water helps keep them cool.
Insulated mugs with lids help keep hot drinks warm longer.
Aluminum foil behind radiators helps keep the house warm by reflecting heat back into the room.
Vacuum flasks reduce energy transfers by radiation, conduction, convection, and evaporation.
Power and Efficiency
How Much Energy Do Different Appliances Use?
The amount of energy transferred per second is the power of the appliance, measured in watts (W) or kilowatts (kW).
1 W = 1 J/s
1000 W = 1 kW
Appliances with higher power ratings transfer more energy each second.
Efficiency is the amount of useful energy transferred compared with the total amount supplied.
efficiency = (useful \, energy \, transferred / total \, energy \, supplied) × 100
Energy cannot be created or destroyed, so the total energy supplied equals the total energy transferred or stored.
Sankey diagrams show energy transfers, with the width of each arrow representing the proportion of energy.
Paying for Energy
How Do We Pay For Energy?
We pay for energy bought as fuel or for the amount of electricity and gas transferred.
Energy companies use kilowatt-hours (kWh) to measure energy; 1 kWh is the energy transferred in 1 hour by a 1 kW appliance.
energy \, use \, (kWh) = power \, rating \, (kW) × time \, (hours)
Insulating houses and using more efficient appliances can save money on energy bills.
Payback time tells you how long it will take to save the money that an efficiency measure costs:
payback \, time = cost \, of \, change / saving \, per \, year
Changing Ideas
Observations of the Sun, Moon, and stars have been recorded for over 5000 years for calendars and religious reasons.
People have known that the Earth is a sphere, but until about 500 years ago, most believed it was the center of everything.
We now use a model of the Solar System with the Sun at the center.
Gathering the Evidence
How Was Our Model of the Solar System Worked Out?
Early astronomers used only their eyes to observe the five visible planets.
Ptolemy developed a model with the Earth in the center, accepted for 1500 years.
Later astronomers made more accurate observations, revealing flaws in Ptolemy's model.
Copernicus suggested that the Earth and planets moved around the Sun in circles.
Galileo's telescope observations supported Copernicus' model.
Kepler's model has the Sun at the center with planets moving in elliptical orbits. Most planets also have moons.
Spacecraft have allowed more detailed investigation of planets.
Seasons
What Causes the Seasons?
The Earth's tilted axis causes seasons.
When the northern hemisphere is tilted towards the Sun, it is summer in Europe.
When the northern hemisphere is tilted away, it is winter.
In summer, the Sun is high in the sky, and days are longer than nights.
In winter, the Sun is not very high, and nights are longer than days.
The Sun feels hotter in the summer because its rays are more concentrated.
Magnetic Earth
What is the Earth's Magnetic Field?
Compasses use magnets to point north, based on the Earth's magnetic field.
The north pole of one magnet attracts the south pole of another; like poles repel.
The space around a magnet where it has an effect is its magnetic field.
The Earth's magnetic field is caused by movements in the liquid part of its core.
Gravity in Space
How Does Gravity Affect the Solar System?
Gravity is a force that pulls any two objects together; the bigger the mass, the stronger the force.
The Earth's gravity pulls objects towards its center.
Weight is the force of gravity pulling on an object, measured in newtons (N).
weight \, (N) = mass \,(kg) × gravitational \, field \, strength \, (N/kg)
The Earth's gravitational field strength is about 10 N/kg.
The force of gravity between the Sun and the Earth keeps the Earth in orbit.
Beyond the Solar System
What is Beyond Our Solar System?
Stars are huge balls of gas that give out large amounts of energy.
The Sun is a star.
Stars appear dim because they are far away.
Galaxies are large groups of stars.
The Sun is in the Milky Way galaxy.
The Universe is made up of millions of galaxies.
Distances between stars are measured in light years; one light year is the distance light travels in one year, approximately 10,000,000,000,000 km.
The nearest star to the Sun is Proxima Centauri, 4.22 light years away.
Transferring Energy
How is Energy Transferred by Heating?
Energy is transferred by heating through evaporation, radiation, conduction, and convection.
Radiation
Energy is transferred from hot objects as infrared radiation. Hotter objects emit more radiation, which can be absorbed or reflected. Radiation travels through waves, doesn't need a medium, and can be focused.
Conduction
Energy transfer through solids involves particles vibrating and passing vibrations through the material. Metals are good conductors; wood and plastics are insulators. Conduction is efficient in solids due to close particle proximity.
Convection
Energy is transferred through fluids (liquids and gases). Heated fluid expands, becomes less dense, and rises, creating a convection current. Cooler fluid replaces the rising warm fluid.
Controlling Energy Transfers
How Can We Control Energy Transfers?
Insulation keeps warmth inside houses. Materials like brick and wood are good insulators. Trapped air insulates well. Light colors and shiny surfaces reflect infrared radiation, keeping houses cool; dark colors absorb it. Insulated mugs and aluminum foil also control energy transfers.
Power and Efficiency
How Much Energy Do Different Appliances Use?
Power measures energy transferred per second in watts (W) or kilowatts (kW). Higher power means more energy transfer. Efficiency is the ratio of useful energy output to total energy input, expressed as a percentage.
Paying for Energy
How Do We Pay For Energy?
Energy is paid for in kilowatt-hours (kWh). Calculating energy use involves multiplying power rating by time. Insulation and efficient appliances save money. Payback time is the cost of change divided by savings per year.
Changing Ideas
Observations have evolved from Earth-centered to a Sun-centered model of the Solar System.
Gathering the Evidence
How Was Our Model of the Solar System Worked Out?
Early models were Earth-centered, but later observations and models by Copernicus, Galileo, and Kepler refined our understanding to a Sun-centered system with elliptical orbits.
Seasons
What Causes the Seasons?
The Earth's tilted axis causes seasons. The hemisphere tilted towards the Sun experiences summer with longer days and more direct sunlight.
Magnetic Earth
What is the Earth's Magnetic Field?
The Earth has a magnetic field caused by movements in its liquid core, which is used by compasses to point north.
Gravity in Space
How Does Gravity Affect the Solar System?
Gravity is a force that attracts objects; its strength depends on mass. It keeps Earth in orbit around the Sun.
Beyond the Solar System
What is Beyond Our Solar System?
Transferring Energy
How is Energy Transferred by Heating?
Energy is transferred by heating through evaporation, radiation, conduction, and convection.
Radiation
Energy is transferred from hot objects as infrared radiation. Hotter objects emit more radiation, which can be absorbed or reflected. Radiation travels through waves, doesn't need a medium, and can be focused.
Conduction
Energy transfer through solids involves particles vibrating and passing vibrations through the material. Metals are good conductors; wood and plastics are insulators. Conduction is efficient in solids due to close particle proximity.
Convection
Energy is transferred through fluids (liquids and gases). Heated fluid expands, becomes less dense, and rises, creating a convection current. Cooler fluid replaces the rising warm fluid.
Controlling Energy Transfers
How Can We Control Energy Transfers?
Insulation keeps warmth inside houses. Materials like brick and wood are good insulators. Trapped air insulates well. Light colors and shiny surfaces reflect infrared radiation, keeping houses cool; dark colors absorb it. Insulated mugs and aluminum foil also control energy transfers.
Power and Efficiency
How Much Energy Do Different Appliances Use?
Power measures energy transferred per second in watts (W) or kilowatts (kW). Higher power means more energy transfer. Efficiency is the ratio of useful energy output to total energy input, expressed as a percentage.
Paying for Energy
How Do We Pay For Energy?
Energy is paid for in kilowatt-hours (kWh). Calculating energy use involves multiplying power rating by time. Insulation and efficient appliances save money. Payback time is the cost of change divided by savings per year.
Changing Ideas
Observations have evolved from Earth-centered to a Sun-centered model of the Solar System.
Gathering the Evidence
How Was Our Model of the Solar System Worked Out?
Early models were Earth-centered, but later observations and models by Copernicus, Galileo, and Kepler refined our understanding to a Sun-centered system with elliptical orbits.
Seasons
What Causes the Seasons?
The Earth's tilted axis causes seasons. The hemisphere tilted towards the Sun experiences summer with longer days and more direct sunlight.
Magnetic Earth
What is the Earth's Magnetic Field?
The Earth has a magnetic field caused by movements in its liquid core, which is used by compasses to point north.
Gravity in Space
How Does Gravity Affect the Solar System?
Gravity is a force that attracts objects; its strength depends on mass. It keeps Earth in orbit around the Sun.
Beyond the Solar System
What is Beyond Our Solar System?
Transferring Energy
How is Energy Transferred by Heating?
Energy is transferred by heating through evaporation, radiation, conduction, and convection.
Radiation
Energy is transferred from hot objects as infrared radiation. Hotter objects emit more radiation, which can be absorbed or reflected. Radiation travels through waves, doesn't need a medium, and can be focused.
Conduction
Energy transfer through solids involves particles vibrating and passing vibrations through the material. Metals are good conductors; wood and plastics are insulators. Conduction is efficient in solids due to close particle proximity.
Convection
Energy is transferred through fluids (liquids and gases). Heated fluid expands, becomes less dense, and rises, creating a convection current. Cooler fluid replaces the rising warm fluid.
Controlling Energy Transfers
How Can We Control Energy Transfers?
Insulation keeps warmth inside houses. Materials like brick and wood are good insulators. Trapped air insulates well. Light colors and shiny surfaces reflect infrared radiation, keeping houses cool; dark colors absorb it. Insulated mugs and aluminum foil also control energy transfers.
Power and Efficiency
How Much Energy Do Different Appliances Use?
Power measures energy transferred per second in watts (W) or kilowatts (kW). Higher power means more energy transfer. Efficiency is the ratio of useful energy output to total energy input, expressed as a percentage.
Paying for Energy
How Do We Pay For Energy?
Energy is paid for in kilowatt-hours (kWh). Calculating energy use involves multiplying power rating by time. Insulation and efficient appliances save money. Payback time is the cost of change divided by savings per year.
Changing Ideas
Observations have evolved from Earth-centered to a Sun-centered model of the Solar System.
Gathering the Evidence
How Was Our Model of the Solar System Worked Out?
Early models were Earth-centered, but later observations and models by Copernicus, Galileo, and Kepler refined our understanding to a Sun-centered system with elliptical orbits.
Seasons
What Causes the Seasons?
The Earth's tilted axis causes seasons. The hemisphere tilted towards the Sun experiences summer with longer days and more direct sunlight.
Magnetic Earth
What is the Earth's Magnetic Field?
The Earth has a magnetic field caused by movements in its liquid core, which is used by compasses to point north.
Gravity in Space
How Does Gravity Affect the Solar System?
Gravity is a force that attracts objects; its strength depends on mass. It keeps Earth in orbit around the Sun.
Beyond the Solar System
What is Beyond Our Solar System?