Transcript Heat-Energy-Transfer

Heat Energy Transfer
SNC2D
The Transfer of Heat Energy
There are 3 different mechanisms by which
heat energy may be transferred:
The Transfer of Heat Energy
There are 3 different mechanisms by which
heat energy may be transferred:
• radiation
The Transfer of Heat Energy
There are 3 different mechanisms by which
heat energy may be transferred:
• radiation
• conduction
The Transfer of Heat Energy
There are 3 different mechanisms by which
heat energy may be transferred:
• radiation
• conduction
• convection
Radiation
Radiation is the release of infrared radiation
by a substance at a higher temperature
than its surroundings.
Radiation
Radiation is the release of infrared radiation
by a substance at a higher temperature
than its surroundings.
This is the only mechanism that works in a
vacuum (outer space, including the space
between the Earth and the Sun).
Conduction
Conduction is the transfer of kinetic energy
(the energy of motion) between particles
in direct contact.
Conduction
Conduction is the transfer of kinetic energy
(the energy of motion) between particles
in direct contact.
Conduction is therefore most effective in
solids.
Convection
Convection is the movement of particles
from one location to another: cooler,
denser material will sink relative to
warmer, less dense material.
Convection is therefore most effective in
liquids and gases.
Solar Radiation
So energy arrives from the Sun in the form
of radiation (both visible and infrared).
However, not all of this energy is absorbed.
Some is reflected. The percentage of
radiation reflected is the albedo of the
surface. Ice and snow reflect sunlight
more than land or ocean.
Solar Radiation
Solar Radiation
Different surfaces also have different
temperature responses to the same heat
energy input.
Solar Radiation
Different surfaces also have different
temperature responses to the same heat
energy input.
E.g. water has a high heat capacity, which
means that it takes more energy to heat
the oceans than the land (which is why
the water at the beach on a summer’s day
is colder than the sand).
Solar Radiation
Also, arriving solar radiation is not
distributed evenly: the equatorial regions
receive, on average, more direct sunlight
than the polar regions.
Heat Transfer on Earth
All this uneven heating of the Earth’s surface
results in the transfer of heat energy
(primarily from the equatorial region to
the poles) by convection in the Earth’s
atmosphere and hydrosphere.
Convection in the Atmosphere
The warm, moist air at the Equator rises and
releases its moisture (resulting in rainforest
biomes) and cools, sinking down at about 30o
North and 30o South latitude (resulting in desert
biomes).
Convection in the Atmosphere
Because the Earth is rotating, the Coriolis Effect
forces the surface air moving toward the
Equator from east to west, resulting in the NE
and SE trade winds.
Convection in the Atmosphere
Similar convection cells between 30oN and 60oN
and 30oS and 60oS latitudes result in prevailing
westerly winds (which is why the weather across
Canada moves from west to east).
Convection in the Hydrosphere
The patterns of ocean currents are complicated by
the position of the continents.
The Effects of Climate Change
It is important to understand how heat
energy transfer affects the climate to
understand how global warming can
change climate.
The Effects of Climate Change
E.g. global warming has resulted in increased
evaporation from the oceans, resulting in
increased precipitation of snow over the
Northern Hemisphere (Siberia in particular),
resulting in increased albedo, resulting in colder
winters.
The Effects of Climate Change
E.g. the increased melting of glaciers and
Arctic ice could result in increased cold
ocean currents from the Arctic, possibly
reversing the North Atlantic Drift that
keeps Europe temperate.
More Practice
p. 289 # 6, 7, 8, 12, 13 p. 292 #7, 16