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Energy and Heat

It Is All Around You…

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You have heard the word “ENERGY” before, but how is it defined by a scientist?

Energy is defined as “the ability to do work.”

the hot steam that comes from a hot iron,

and this glass that is about to fall on the floor.

the electricity that comes into our homes,

the food we eat,

…the sunlight that warms your face,

Energy is all around us. Energy is all around us. Examples include…Examples include…

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Five Main Forms of Energy

NuclearNuclear

ElectricityElectricity

ChemicalChemical

HeatHeat

MechanicalMechanical

(Atoms In Motion)

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MechanicalMechanicalDid 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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ChemicalChemical

A substance is changed from one form to another.

This energy released is in the bonds of This energy released is in the bonds of atoms.atoms.

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ElectricalElectrical(examples)(examples)

Static electricity is released when lightning strikes.

Electrical current is the movement of electrical charges.

Chemical Electrical Mechanical Electrical

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NuclearNuclearThere is energy at the atomic

level.

Energy

Energy

Energy

Nuclear FissionSplitting the Atom

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Heat Heat is a form of ENERGY.

Atoms are constantly moving.

Heat is produced with the motion of atoms.Heat is produced with the motion of atoms.

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HeatHeat and Kinetic Energy and Kinetic EnergyEnergy of Motion at the Atomic

LevelThe atoms to the left demonstrate kinetic energy because they are moving. All atoms move (vibrate)

except at absolute zero (-273oK or -459oF) where ALL motion stops.

The more heat is produced, the higher the temperature.

The faster the atoms move, the more heat is produced.

For more on absolute zero go to: http://www.colorado.edu/physics/2000/bec/temperature.html

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ConductionConductionOuch!

…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.

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Air above the flame heats and expands and you feel the heat transferring into

your hand.

Cool water is pushed downCool water is pushed down

As the heated water rises…As the heated water rises…

ConvectionConvection…is the transfer of heat by the actual motion of a

fluid (liquid or gas) in the form of currents.

The heated water rises as

the cooler water is

pushed down. The water that was

pushed down is then heated

and …

then rises pushing the now

cooler water down.

This causes a current in the

water.

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RadiationRadiation…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 HeatSpecific 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

Aluminum

Copper

Glass

Ice (-20 to 0 0 C)

Iron

Mercury

Ocean Water

Water

Wood

0.25

0.22

0.09

0.20

0.50

0.11

0.03

1.00

0.42

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 ProblemHow much heat is needed to raise the temperature of 4 grams of aluminum 5 oC?Q = M x T x C

Q =

M =

T=

C =

?

4 g

5 oC

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 =

M =

T=

C =

16.5 calories

10 g

15 oC

?

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

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

Let’s do the math16.5 Cal. 10g x 15 oC = 0.11 cal/g

oCIf you look on the chart, you find out that’s iron!

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Potential Energy…

Kinetic Energy…

can also be called stored energy (energy is not being used). Example: the chemical energy stored in a stack of coal.

can also be called energy of motion. When this locomotive engine uses the coal, it becomes energy of motion.

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Potential EnergyPotential 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 The Pull of GravityGravity

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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.