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A vivid demonstration that heat is a form of motion. A smallamount of boiling water is poured into the empty can, which rapidly fillsup with hot steam. The can is then sealed tightly, and soon crumples.This can be explained as follows. The high temperature of the steam isinterpreted as a high average speed of random motions of its molecules.Before the lid was put on the can, the rapidly moving steam moleculespushed their way out of the can, forcing the slower air molecules out ofthe way. As the steam inside the can thinned out, a stable situation wassoon achieved, in which the force from the less dense steam moleculesmoving at high speed balanced against the force from the more dense butslower air molecules outside. The cap was put on, and after a while thesteam inside the can reached the same temperature as the air outside.The force from the cool, thin steam no longer matched the force from thecool, dense air outside, and the imbalance of forces crushed the can.form of energy is important in a particular situation. For instance,the spinning coin in figure s gradually loses its kinetic energy, andwe might think that conservation of energy was therefore being violated.However, whenever two surfaces rub together, friction actsto create heat. The correct analysis is that the coin’s kinetic energyis gradually converted into heat.One way of making the proliferation of forms of energy seem lessscary is to realize that many forms of energy that seem different onthe surface are in fact the same. One important example is thatheat is actually the kinetic energy of molecules in random motion,so where we thought we had two forms of energy, in fact there isonly one. Sound is also a form of kinetic energy: it’s the vibrationof air molecules.This kind of unification of different types of energy has been aprocess that has been going on in physics for a long time, and atthis point we’ve gotten it down the point where there really onlyappear to be four forms of energy:22 Chapter 1 Conservation of Mass and Energy
1. kinetic energy2. gravitational energy3. electrical energy4. nuclear energyWe don’t even encounter nuclear energy in everyday life (except inthe sense that sunlight originates as nuclear energy), so really formost purposes the list only has three items on it. Of these three,electrical energy is the only form that we haven’t talked about yet.The interactions between atoms are all electrical, so this form ofenergy is what’s responsible for all of chemistry. The energy in thefood you eat, or in a tank of gasoline, are forms of electrical energy.Section 1.4 Conservation of Energy 23
Page 2 and 3: copyright 2006 Benjamin Crowellrev.
Page 4 and 5: ContentsMomentum compared to kineti
Page 7 and 8: Chapter 1Conservation of Mass andEn
Page 9 and 10: 1.2 Conservation of MassWe intuitiv
Page 11 and 12: masses on the spring, and they both
Page 13 and 14: A common source of confusion is the
Page 15 and 16: Discussion questionA Each of the fo
Page 17 and 18: l / Galileo Galilei was the first p
Page 19 and 20: that this wasn’t really an argume
Page 21: the girl on the left goes up a cert
Page 25 and 26: In fact, your body uses up even mor
Page 27 and 28: kinetic energy is twice as much. Bu
Page 29 and 30: ather than flying off straight. New
Page 31 and 32: of mass?Actually they’re not even
Page 33 and 34: ecause the square of the speed of l
Page 35 and 36: ProblemsKey√∫⋆A computerized
Page 37 and 38: 13 How high above the surface of th
Page 39 and 40: Chapter 2Conservation ofMomentumFan
Page 41 and 42: win the Martian version of the Nobe
Page 43 and 44: a / How can we prove that this coll
Page 45 and 46: all.This is exactly like the rules
Page 47 and 48: Unequal masses example 4⊲ Suppose
Page 49 and 50: ForceDefinition of forceWhen moment
Page 51 and 52: ent relationship:(fingers on scale)
Page 53 and 54: pressed in modern units). If the ea
Page 55 and 56: p / A bowling ball is in the back o
Page 57 and 58: Kepler’s law of periodsLet T , ca
Page 59 and 60: 2.5 WorkImagine a black box 8 , con
Page 63 and 64: A tornado touches down in Spring Hi
Page 65 and 66: pensated for by an overall increase
Page 67 and 68: Kepler’s equal-area law example 4
Page 69 and 70: Torque distinguished from forceOf c
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Chapter 4RelativityComplaining abou
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motion of the apparatus. For instan
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fore Einstein. In fact, George Fitz
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We are used to thinking of time as
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j / In the garage’s frame of refe
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is now sufficiently advanced to all
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astronauts had twin siblings back o
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The derivation of the correct relat
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efore the collision0 1.60.9 0.7afte
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e the same as they always were. The
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(b) Show that your result is approx
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Chapter 5ElectricityWhere the teles
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to the egg.Luckily, we now know eno
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“A” as negative, but it really
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The main subtlety involved in this
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Note that an example like g/3 does
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⊲ An ampere-hour is a unit of cur
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portional to the voltage difference
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ing your feet on a carpet, and then
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ProblemsKey√∫⋆A computerized
Page 113 and 114:
This sunspot is a product of the su
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directions strongly evokes wave met
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The electric fieldThe definition of
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trical interaction. This seems like
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except that the bottom charge is no
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q / The force on a charged particle
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time it took for the black coil’s
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charge, there will be magnetic fiel
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z / Panel 1 shows the electromagnet
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used to make images of individual a
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Chapter 7The Ray Model of Light7.1
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Today, photography provides the sim
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Interaction of light with matterAbs
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g / Examples of ray diagrams.h / Th
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in their passing out of one medium
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Figure k shows what happens if you
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m / At double the distance, the par
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infrared, you don’t emit visible
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infinitesimally from it. In figure
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physical shape of the mirror’s su
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Sketch another copy of the face in
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Discussion questionsA The figure sh
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DLocate the images formed by the pe
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Problem 2.4 In this chapter we’ve
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signals to travel between you and t
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“The Great Wave Off Kanagawa,”
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amplitude, A. The definition of amp
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a single hump or trough. If you hit
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Surfing example 3The incorrect beli
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Sound wavesThe phenomenon of sound
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do they signify in the case of a wa
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⊲ Solving for wavelength, we have
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ProblemsKey√∫⋆A computerized
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Appendix 1: Photo CreditsExcept as
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Appendix 2: Hints and SolutionsAnsw
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cm, and the distance from the axis
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Foucault, Léon, 17frame of referen
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twin paradox, 83units, conversion o
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Commons

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