168 Science and Technology
Everything around us contains heat. Heat is
a form of energy – the energy of the random
jiggling motion of particles that make up all
matter. .TEMPERATURE is a measure of
how hot an object is – it can be recorded
using a .THERMOMETER.
WHAT ARE THE THREE TYPES OF HEAT TRANSFER?
Conduction is the transfer of heat from one molecule
to another. Energetic molecules pass on heat energy
when they collide with less energetic molecules.
Convection is the transfer of heat through a liquid
or a gas as warm fluid rises and cool fluid sinks.
These movements are convection currents. Radiation
is the movement of heat by electromagnetic rays.
All objects emit radiation.HOW DOES HEAT FLOW?
Heat always flows from a higher temperature to a
lower temperature. If you stand next to a radiator,
the heat from it warms you up. Different materials
let heat flow through them at different rates. Metals
are the best conductors (they let heat flow easily).. THERMAL INSULATORS don’t conduct heat well.
CAN WE SEE HEAT?
We cannot see heat, but we can see its effects.
Convection currents rising from a hot tarmac road
make the air above shimmer. A thermal-imaging
camera detects radiation emitted by hot objects.
Electronics convert invisible electromagnetic rays
into an image on a television screen.THERMOGRAPH 1
This false-colour image shows the temperature differences over a
man’s head and shoulders. Thermal imaging cameras installed at
airports can spot passengers with a fever (higher than normal
temperature) who may be carrying an infectious disease. They are
also used at ports to detect people smuggled in vehicles.1 THERMAL-IMAGING
Rescue workers use a thermal-imaging camera to search for survivors in
dense smoke or under fallen rubble. A warm body shows up as a bright
area in the image.Heat
Red and yellow
regions are
warmestBlue and
green regions
are coolestThe nose loses heat
easily because it
does not contain
many blood vesselsEyes are hot areas
because they contain
lots of blood vessels