Energy can be transferred in three ways
Radiation Transfers Energy
Energy can be transferred even though there are no particles to transfer the energy. This type of energy
transfer is called radiation. Radiation is the transfer of energy without any movement of matter. Energy that is transferred
in this way is called radiant energy or electromagnetic radiation (EMR for short).
Radiant energy travels in waves (much like a tsunami).
These waves can travel through space, air, glass and many other materials. There are different forms of EMR,
including radio waves, microwaves, visible light and X-rays.
If the energy source is a warm object, like the sun, some of the thermal energy is transferred
as a type of EMR called infrared radiation (IR) or 'heat
Properties (characteristics) of Radiant Energy are:
Waves of radiant energy can travel in a vacuum.
All waves travel, across empty space, at an extremely high speed (300 Million m/s).
Radiant energy travels in a straight line.
they behave like waves
they can be absorbed and reflected by objects
All kinds of radiant energy interact with matter:
Reflection occurs if the energy cannot penetrate the surface of the material it comes into contact
Absorption occurs if the energy penetrates part way into the object.
Transmission occurs if the energy penetrates completely, passing through the object with no absorption
Absorbing / Emitting Energy
Dull dark objects absorb radiant energy when they are cool, and emit radiant energy when
they are hot. (eg. asphalt sidewalk)
Light, shiny objects or surfaces do not absorb radiant energy readily and do not emit radiant energy readily. (eq.
Radiant emission of energy from the body depends on surface area (smaller areas help to retain heat, whereas, larger
areas radiate heat). This is evident in the adaptations of many species of animals who have successfully adapted
to their environments.(desert animals - eg. Fox p. 140) (killer whales-The killer whale's fusiform body shape and
reduced limb size decreases the amount of surface area exposed to the external environment. This helps killer whales
conserve body heat.) The polar bear has black skin to absorb radiant energy with transparent hair that transmitts
ultraviolet radiation to the skin.
Most radiation (82%) people are exposed, to comes from natural sources. By far the largest source
is radon, an odorless, colorless gas given off by natural radium in the Earth's crust. Artificial radiation, mostly
from medical uses and consumer products, accounts for about eighteen percent of our total exposure. The nuclear
industry is responsible for less than one percent.
Radiation can be detected, measured and
The measurement of radiation is by the amount of radioactivity present
or the amount of radiant energy given off.
Radiation in the Environment
Radiation is a natural part of our environment. Humans have always lived on earth in
the presence of radiation. Natural radiation reaches earth from outer space and continuously radiates from the
rocks, soil, and water on the earth. Background radiation is that which is naturally and inevitably present in
our environment. Levels of this can vary greatly. People living in granite areas or on mineraliscd sands receive
more terrestrial radiation than others, while people living or working at high altitudes receive more cosmic radiation.
A lot of our natural exposure is due to radon. a gas which seeps from the earth's crust and is present in the air
Conduction, Energy Through Solids
In solids, where the particles are closely packed together, thermal energy can be transfered
from one particle to another very easily. Thermal
conduction is the process of transferring
thermal energy by the direct collisions of the particles. The spaces between the particles, in different solids,
determines how quickly these collisions can take place. Good conducting materials are those materials where there
is little space between the particles - like most metals. Poor conductors, like glass and wood are called heat insulators. These insulators when wrapped around an object slow
down the rate of thermal conduction.
Metals are good conductors of heat, so they are used extensively in cooking, because they transfer
heat efficiently from the stove top or oven to the food.
Hot and cold packs are used to treat muscle injuries.
Lamp (The Davy Lamp) Davy invented his miner's safety helmet in 1815. The lamp of this
safety helmet would burn safely and emit light even when there was an explosive mixture of methane and air present.
Davy did not patent the lamp. (see explanation - Did You Know - p. 127)
The Radiator of a car transfers heat away from the engine, so that the gasoline being used will
not ignite. (Antifreeze is used to achieve this)
The use of diamonds to transfer the heat generated by small electronic devices. Diamonds are called
"ice" with good reason. Objects feel cold not only because they are at a lower temperature than our bodies,
but also because they can transfer or conduct the heat away from us. When you touch a diamond to your lips, it
feels ice-cold because it robs your lips of their heat. The capacity of a diamond to conduct heat distinguishes
it readily from other gems and exceeds that of copper, an excellent thermal conductor, by about 4 times at room
temperature. This exceptional property of diamond is increasingly being used for extracting heat from electronic
devices to make them smaller and more powerful.
A Great Science Resource can be found at Science Net.
Convection, Energy on the Move
Thermal energy can be transferred by fluids in a third way, by the circular motion of the particles,
In convection, the warmer particles transfer their energy to the cooler particles as they move
in a circular pattern, called a convection current. A simple experiment
lamps are good examples to see this in action.
Birds and para-gliders make use of 'thermals' to help them soar and glide - helping them to conserve
energy when they migrate.
Convection currents are also involved in creating the force of magnetism that surrounds the earth.
The convection oven is another of the many practical applications of convection.
The heat inside the oven, helps to provide uniform beating as the convection current transfers the
heat evenly inside the oven.
Heating occurs through currents in a fluid, such as radiator water heating and flowing from the
basement to heat a radiator on a floor above.
Analyzing Energy Transfer Systems
What happens when energy is transferred? The energy is not lost, it is only changed.
Particles allow this transfer of energy to take place. The example of a Volleyball is given in the textbook on
Carrie's energy in her fist transferred to the ball, which transferred it to the floor. Conduction
occurred, when the energy in her fist was conducted by the particles in her fist to the particles in the ball.
The particles in the ball conducted the energy to the particles in the floor. The particles in the air were also
warmed by the flight of the ball and the particles transferred this energy by convection currents which were created
in the air.
Features of Energy Transfer Systems
All energy systems have five common features:
Energy Source - this is where the energy comes from that can be transferred throughout
the energy system. The energy source can be mechanical, chemical, radiant, nuclear or electrical.
Direction of Energy Transfer - energy is always transferred away from the concentrated
sources. Changes in non-living systems spread out the energy evenly.
Transformations - energy can change its form when it is transferred
Waste Heat - almost all of the energy is transferred directly from particle to particle,
but some of the energy can be lost to the surroundings.
Control Systems - a control device can start and stop the transfer of energy (a thermostat
in a home heating system)
Topic Review p. 236
Wrap-Up (Topics 4-6) p. 237