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EW&A 3.2 Energy Transfer
Hot and Cold
How are energy and temperature related?
• All matter is made up of moving particles and has kinetic energy.
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Temperature is a measure of the average kinetic energy of particles.
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The faster a particle moves, the more kinetic energy it has.
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Thermal energy is the total kinetic energy of particles.
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Thermal energy depends on the number of particles.
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The more particles there are in an object, the greater its thermal energy.
How does kinetic energy change as particle motion increases and decreases?
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What is thermal expansion?
As the space between particles increases, a substance expands.
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The increase in volume that results from an increase in temperature is called thermal expansion.
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Thermal expansion causes a change in the density of a substance.
Density is the mass per unit volume of a substance.
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Differences in density caused by thermal expansion can cause movement of matter.
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The movement of air in the atmosphere, water in the oceans, and rock in the geosphere can be
caused by thermal expansion.
Getting Warm
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What is heat?
Heat is the energy that is transferred between objects that are at different temperatures.
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When objects at different temperatures come in contact, energy is transferred between them until
they reach the same temperature.
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Energy flows from the object at higher temperature to that at lower temperature.
Why can the temperatures of land, air, and water differ?
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The different rates at which materials become warmer or cooler are due to specific heat.
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Materials with a high specific heat require more energy to show an increase in temperature.
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Water has a higher specific heat than land, which means water warms up and cools down more
slowly than land does.
Heat
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How is energy transferred by radiation?
Radiation is the transfer of energy as electromagnetic waves.
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The sun transfers energy to Earth by radiation.
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Radiation can transfer energy between objects that are not in direct contact with each other.
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Energy from the sun travels as waves and is called electromagnetic radiation.
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Forms of electromagnetic radiation include visible light, infrared radiation, X-rays, and ultraviolet light.
How does the sun heat Earth?
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Where does radiation occur on Earth?
The sun is almost 150 million km away from Earth, but it is the major source of energy for processes
on Earth.
Solar radiation is partly reflected and scattered by Earth’s atmosphere. However, some solar radiation
is absorbed by the atmosphere, geosphere, and hydrosphere.
Heating Up
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How is energy transferred by convection?
Convection is the transfer of energy due to the movement of matter.
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Convection occurs because most matter becomes less dense when it gets warmer.
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Convection currents form as warm and cool matter rise and fall due to temperature and density
differences.
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Where does convection occur on Earth?
Energy moves through the atmosphere as warm air rises and cool air sinks.
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Ocean water has different densities due to differences in temperature and the amount of salt in the
water.
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Energy is transferred through rock material from Earth’s core to the surface by convection currents.
Ouch!
How is energy transferred by conduction?
• Conduction is the transfer of energy from one object to another object through direct contact.
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When objects at different temperatures touch, their particles interact.
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The faster-moving particles of the warmer object transfer energy to the slower-moving particles in the
cooler object.
Where does conduction occur on Earth?
• Energy is transferred by conduction from the warmer ground to cooler air at Earth’s surface.
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Warm air can transfer energy to cooler water and cause evaporation. If water vapor transfers energy
to the air, the water vapor may condense.
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Inside Earth, energy can be transferred between rock particles by conduction, but very slowly.