Transcript Energy and Heat

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Energy and Heat
It Is All Around You…
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Energy is all around us.
Examples include…
…the sunlight that
warms your face,
the food we eat,
the electricity that comes
into our homes,
the hot steam that
comes from a hot iron,
and this glass that is
about to fall on the floor.
You have heard the word “ENERGY” before,
but how is it defined by a scientist?
Energy is defined as “the ability to do work.”
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Five Main Forms of Energy
Mechanical
Nuclear
Chemical
Electricity
Heat
(Atoms In Motion)
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Mechanical
Did you know that a
waterfall has energy?
Mechanical energy is defined as
“matter in motion.”
How do these examples demonstrate mechanical energy?
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Chemical
A substance is changed from
one form to another.
This energy released is in the bonds of atoms.
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Electrical
(examples)
Static electricity is released when
lightning strikes.
Electrical current is the movement of electrical charges.
Chemical  Electrical
Mechanical  Electrical
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Nuclear
There is energy at the atomic level.
Energy
Energy
Energy
Nuclear Fission
Splitting the Atom
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Heat
is a form of ENERGY.
Atoms are constantly moving.
Heat is produced with the motion of atoms.
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Heat and Kinetic Energy
Energy of Motion at the Atomic Level
The atoms to the left demonstrate
kinetic energy because they are moving.
All atoms move (vibrate) except at
o
o
absolute zero (-273 K or -459 F) where
ALL motion stops.
The faster the atoms move,
the more heat is produced.
The more heat is produced,
the higher the temperature.
For more on absolute zero go to:
http://www.colorado.edu/physics/2000/bec/temperature.html
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Ouch!
Conduction
…is the transfer of heat by the
direct contact of particles of
matter.
The heat of the
boiling liquid
directly contacts
the metal spoon
and causes the
spoon to transfer
the heat to the
hand.
Convection
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…is the transfer of heat by the actual motion of a fluid
(liquid or gas) in the form of currents.
Cool water is pushed down
The heated
water rises as
the cooler water
is pushed down.
The water that
was pushed
down is then
heated and …
Air above the flame heats and
expands and you feel the heat
transferring into your hand.
then rises pushing
the now cooler
water down.
This causes a
current in the
water.
As the heated water rises…
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Radiation
…is heat transfer by
electromagnetic waves.
MATTER is not necessary for
this transfer of heat.
A common type of radiation comes
from the sun. Examples include –
• Ultraviolet
• Visible Light Color spectrum –
(ROYGBIV)
• Infrared
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Specific Heat
• The definition of
specific heat is a
substance’s ability
to absorb heat.
– This chart lists
specific heat for
various materials.
Substance
Specific Heat
Air
0.25
Aluminum
0.22
Copper
0.09
Glass
0.20
Ice (-20 to 0
0
C)
0.50
Iron
0.11
Mercury
0.03
Water
1.00
Wood
0.42
Ocean Water
0.93
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Calculating Heat Energy:
• The formula:
Heat loss or gain (Q) = Mass x Temperature(T) x
Specific Heat of the material (C)
In short:
Q = M x T x C
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The Problem
How much heat is needed to raise the temperature of 4
Q = M x T x C
grams of aluminum 5 oC?
Q=
?
M= 4g
o
T= 5 C
C=
0.22
(from the chart)
We need to figure out “Q” so we can
leave the formula as it is:
Q = M x T x C
4g X 5 oC X 0.22 cal/g oC = 4.4
calories
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A 10 gram sample of a
“mystery substance” gained
16.5 calories of heat when the
temperature changed 15 oC.
What is the specific heat of
that substance? Look on the
chart to determine the
“mystery substance.”
Q =
16.5 calories
M =
10 g
T=
15 oC
C =
?
We need to figure out “C” so we have to
rearrange the formula. We want “C” to be
alone on one side of the equal sign.
Q = M x T x C
We don’t want mass and temperature on the
right, so we can divide both sides by “M x T”
and cancel.
Q = M x T x C
M x T M x T
… you are left with
Q
M x T = C
Let’s do the math
16.5 Cal.
10g x 15 oC
= 0.11 cal/g oC
If you look on the chart, you find out that’s iron!
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Potential Energy…
can also be called stored energy (energy is
not being used). Example: the chemical
energy stored in a stack of coal.
Kinetic Energy…
can also be called energy of motion.
When this locomotive engine uses the
coal, it becomes energy of motion.
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Potential Energy
Which glass has
the most potential
energy?
Because the glass on the
left is on a higher table, it
has more potential
energy. It will hit the floor
with more energy than
the one on the right.
What is the source of
potential energy in this
example?
The Pull of Gravity
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Heat vs Temperature
• Heat is Energy
– Movement of atoms
– Total kinetic energy of
molecular motion in a
substance.
– Depends on speed,
number (size and mass),
and type of particles.
–
–
http://fs.sdsu.edu/pisces/WeatherKit/Lesson05.php#3
• Temperature is a
measure of Energy
– Thermo =heat
– Meter = to measure
– Measurement of the
average kinetic
energy of molecular
motion in a substance.
– Does not depend on the
speed or type of particle.