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Welcome to SCIE 150:
The Science of Everything

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Last Class

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Today: Energy (Chapter 2)
• Contrast the general properties of the different forms of energy.

• Articulate the difference and relation between
Energy, Power and Work.
• Compare the concepts of Temperature with Heat.
• Examine the implications of the laws of
Thermodynamics in our lives.

• Explore possible sources of energy for our society.

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Energy
• Doing anything requires energy
• Everyday life “energy” = exuberance
• Physics takes it more seriously: the capacity to do work

• What types of energy can you think of offhand?

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Two major types: potential, kinetic

Stored energy

Energy of something in motion, something happening

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Laws of Thermodynamics
• 1st: Energy is conserved
• 2nd: Energy always goes from more useful to less useful forms
▫ There’s no such thing as a free lunch
▫ Everything is taxed...

• 3rd: disorder (entropy) increases

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Energy – a conserved quantity
• Energy is conserved. What does this mean?

• Can’t be created or destroyed
▫ I can’t suddenly blast off into space
▫ I can’t easily stop a speeding car

• But it can be converted from one form to another
▫ I can eat a chocolate bar, and literally get more energy for running
▫ I can shine a light on a solar panel, and get electrical power for a device

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Transferring Energy

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Doing work = the transfer of energy
• You have some money (energy), and in order to do something with it, you have to spend it (do work) 10

Doing Work
• Doing work = transferring energy
• Energy = capacity to do work
• Basic work: force applied through a distance
• The unit of energy (and work): the joule (J)
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1 J: lifting a litre bottle of water 10cm
1 slice of cherry pie = 2,000,000 J
Bicycling or rowing: 1,000 J per second
Flashlight battery stores 10,000 J

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Power
• Power = Energy/time
▫ Watts = Joules/s
▫ A rate of energy flow

• Which uses more power? A:
• Which uses more energy? • Which do you think you get B: billed for?

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Kinetic Energy
• Energy of motion
• What factors determine it?

• Getting rid of it isn’t easy... 13

Radiative Energy

• What type of light carries the most energy?
• A) Radio B) Visible C) Ultraviolet D) Gamma rays

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Sound Energy

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What makes this dangerous?

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Potential Energy

• Elastic, chemical, electrical, gravitational

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Another Potential Energy
• Fat Man and Little Boy
▫ The bombs dropped over Nagasaki and
Hiroshima

• Do they have potential energy? • What kind?

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Mass-Energy
Energy = mass x (speed of light)2
E=mc2

• 1-megaton H-bomb converts mass of a quarter of a can of soda into energy
• The Sun turns some of its mass into energy
• The Big Bang turned a whole lot of energy into the mass of the universe

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Storing Energy
• We live in an electric world
• How do we store electrical energy that we’ve produced? 20

Gravitational Potential Energy and Kinetic Energy

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I dare you to physics

Hold a bowling ball to your nose
Release it

• Energies involved? Energy loss?

Should you move your face? 22

Back and Forth

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Energy Loss?
• 2nd: Energy always goes from more useful to less useful forms
▫ There’s no such thing as a free lunch
▫ Everything is taxed...

• Object pushed on a carpet slides to a stop, what happens to its kinetic energy?
A. It disappears
B. It is turned into heat via friction
C. It is unchanged
D. It is stored as potential energy

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Friction to Heat

• Friction does work, transferring the energy from
“useful” kinetic to “waste” heat

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Kinetic Energy and Temperature
• Particles (atoms and molecules) of any material/object always moving…
• Temperature is average kinetic energy of particles.

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Temperature Scales

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Heat Flows
• Heat always flows from