Unit c - 2.4 & 2.5 -- conduction, convection, and radiation
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Transcript of Unit c - 2.4 & 2.5 -- conduction, convection, and radiation
2.4 & 2.5 CONDUCTION,
CONVECTION, AND RADIATION
WHAT IS CONDUCTION? In the previous sections we looked at
heat energy.This is energy that transfers from high
temperature to low temperature
Conduction is an example of heat energy taking place
Conduction – is the transfer of energy between two substances in contact
EXAMPLE Imagine you have a metal spoon in a
mug of hot chocolate
HOW THIS WORKS Because the particles inside the hot
chocolate are moving faster than those in the spoon –energy gets transferred
This energy transfer will increase the speed of the spoons particles increasing its own temperature
The parts of the spoon not touching the hot chocolate will slowly warm up as well
CONDUCTION AND CONDUCTORS Heat transfer only occurs in one
directionHot Cold or High kinetic energy low kinetic energy
Kinetic energy means the amount of movement
Conduction is most common in solidsLess common in liquidsRARE in gases
CONDUCTORS Conductors – are materials that allow
easy transfer of heat
Different materials allow different amounts of heat to be exchangedThe better the conductor the more heat that
can be transferred
Metal is a very good example of a GOOD conductor
INSULATORS Many solid items conduct heat, but not
all allow a lot to be transferred.
Insulators are materials that Do Not allow easy transfer of heat from a hot substance to a cold substance
Plastics, Cork and Wood are good examples of INSULATORS
HOW DO WE USE THEM Have you ever touched a pot on the
stove and burnt your hand?
Curled your hair and touched the metal?
To avoid injury we commonly combine Insulators & Conductors in order to create tools we can safely use
FIND THE CONDUCTOR AND INSULATOR
CONVECTION Heat is transferred when liquid or gas
particles move from one area to another.
In convection the particles move, in conduction only heat moves
Convection ONLY occurs in liquids and gases
CONVECTION CURRENTS Heat transfer by convection occurs
when particles in a liquid or gas move in a circular pattern.
These currents form when heat is transferred to the liquid or gas
EXAMPLE – BOILING WATER When pot of water is placed on a hot stove the
heat from the stove travels through the conductors and speeds up the particles in the water
The increased particle speed of the water on the bottom causes the water to move to the surface
This pushes the cooler water down to be heated by the stove
The water that moves away from the heat slightly cools and the process repeats itself
CONVECTION CURRENTS IN AIR Heat moves only one direction
From hot to cold
With the air the circular motion still is present
The warmer air will rise pushing the colder air down towards the heat and the cycle continues
RADIATION The third form of heat transfer, only one that
does not rely on movement of particles
Radiation is the transfer of energy through invisible waves Some travel great distances, such as; The Sun
Energy transferred from its source is called Radiant Energy
Heat is one type of energy, another is invisible infrared waves
HOW DOES RADIATION WORK? When these waves hit an object the
kinetic energy (movement) increases
The particles move faster and the object becomes hotter.
Every hot object gives off some radiant energyThis is how you feel the heat of a stove
without touching it
EXAMPLE – HOT CAR Have you every gone into a car that has
been sitting in the sun on a very hot summer day?
What does it feel like?
What happens when you touch the dashboard?
This is a result of the radiant energy from the sun, transferring heat to the car
REFLECT OR ABSORB Can anyone tell me why people tend to
wear more black clothes in the winter compared to summer?
Why does sand burn your feet when you walk on it?
Shiny or Light color objects reflect the radiant energy
Dark or dull color objects absorb radiant energy