book

Head First Physics

Name: Head First Physics
Author: Heather Lang
ISBN: 9781491949924

by Heather Lang

September 2008

Beginner

942 pages

26h 16m

English

O'Reilly Media, Inc.

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Head First Physics: A learner’s companion to mechanics and practical physics
Dedication
A Note Regarding Supplemental Files
Advance Praise for Head First Physics
Praise for other Head First academic titles
Praise for the Head First Approach
Author of Head First Physics
How to Use this Book: Intro
Who is this book for?Who should probably back away from this book?We know what you’re thinkingWe know what your brain is thinkingMetacognition: thinking about thinkingHere’s what WE did:Here’s what YOU can do to bend your brain into submissionRead MeThe technical review team
Acknowledgments
Safari® Books Online

1. Think Like a Physicist: In the beginning ...
Physics is the world around youYou can get a feel for what’s happening by being a part of itSo - could you ever escape from the bottomless pit?Use your intuition to look for ‘special points’The center of the earth is a special pointAsk yourself “What am I ALREADY doing as I reach the special point?”Where you’re at - and what happens next?Now put it all togetherYour Physics Toolbox
2. Making it all MEAN Something: Units and measurements
It’s the best music player ever, and you’re part of the team!So you get on with measuring the myPod caseWhen the myPod case comes back from the factory......it’s waaay too big!There aren’t any UNITS on the blueprintYou’ll use SI units in this book (and in your class)You use conversion factors to change unitsYou can write a conversion factor as a fractionNow you can use the conversion factor to update the blueprintYou just converted the units for the entire blueprint!But there’s STILL a problem ...What to do with numbers that have waaaay too many digits to be usableHow many digits of your measurements look significant?Generally, you should round your answers to three significant digitsYou need to follow certain rules when you’re rounding answersIs it OK to round the myPod blueprint to three significant digits?You ALREADY intuitively rounded your original myPod measurements!Any measurement you make has an error (or uncertainty) associated with itThe error on your original measurements should propagate through to your converted blueprintRight! Time to attack the blueprint again!STOP!! Before you hit send, do your answers SUCK?!You nailed it!When you write down a measurement, you need the right number of significant digitsYour Physics Toolbox
3. Scientific Notation, Area, and Volume: All numbers great and small
A messy college dorm roomSo how long before things go really bad?Power notation helps you multiply by the same number over and overYour calculator’s power button gives you superpowersYour calculator displays big numbers using scientific notationScientific notation uses powers of 10 to write down long numbersScientific notation helps you with small numbers as wellYou’ll often need to work with area or volumeLook up facts in a book (or table of information)Prefixes help with numbers outside your comfort zoneScientific notation helps you to do calculations with large and small numbersThe guys have it all worked out200,000,000 meters cubed bugs after only 16 hours is totally the wrong size of answer!Be careful converting units of area or volumeSo the bugs won’t take over ... unless the guys sleep in!Question Clinic: The “Converting units of area or volume” QuestionYour Physics Toolbox
4. Equations and Graphs: Learning the lingo
The new version of the Break Neck Pizza website is nearly ready to go live ......but you need to work out how to give the customer their delivery timeIf you write the delivery time as an equation, you can see what’s going onUse variables to keep your equation generalYou need to work out Alex’s cycling timeWhen you design an experiment, think about what might go wrong!OK - time to recap where you’re at...Conduct an experiment to find out Alex’s speedHere’s what happens:Write down your results... in a tableUse the table of distances and times to work out Alex’s speedRandom errors mean that results will be spread outA graph is the best way of taking an average of ALL your resultsUse a graph to show Alex’s time for ANY distanceThe line on the graph is your best estimate for how long Alex takes to cycle ANY distanceYou can see Alex’s speed from the steepness of the distance-time graphAlex’s speed is the slope of the distance-time graphNow work out Alex’s average speed from your graphYou need an equation for Alex’s time to give to the web guysRearrange the equation to say “Δ time = something”Use your equation to work out the time it takes Alex to reach each houseSo you do a test run with the website ...So just convert the units, and you’re all set...right?Include the cooking time in your equationThe Break Neck website goes live, and the customers love it!A few weeks later, you hear from Break Neck againA graph lets you see the difference the stop lights madeThe stop lights change Alex’s average speedAdd on two minutes per stop light to give the customer a maximum delivery time ......the customers are extremely happy ......and you’re invited to the Pizza PartyQuestion Clinic: The “Did you do what they asked you” QuestionYour Physics Toolbox
5. Dealing with Directions: Vectors
The treasure huntDisplacement is different from distanceDistance is a scalar; displacement is a vectorYou can represent vectors using arrowsYou found the next clue...But there’s a problem ...You can add vectors in any orderWell done - you’ve found the third clue!Question Clinic: The “Wheat from the chaff” QuestionAngles measure rotationsNow you can get on with clue 3!If you can’t deal with something big, break it down into smaller partsYou move onto the fourth clue...Velocity is the ‘vector version’ of speedWrite units using shorthandSo, on to clue 4 ...You need to allow for the stream’s velocity too!If you can find the stream’s velocity, you can figure out the velocity for the boatIt takes the boat time to accelerate from a standing startHow do you deal with acceleration?So it’s back to the boat ...Vector, Angle, Velocity, Acceleration = WINNER!!!Your Physics ToolboxQuestion Clinic: The “Design an experiment” Question
6. Displacement, Velocity, and Acceleration: What’s going on?
Just another day in the desert ......and another Dingo-Emu moment!How can you use what you know?The cage accelerates as it falls‘ Vectorize’ your equationYou want an instantaneous velocity, not an average velocityYou already know how to calculate the slope of a straight line...A point on a curved line has the same slope as its tangentThe slope of something’s velocity-time graph lets you work out its accelerationWork out the units of accelerationSuccess! You worked out the velocity after 2.0 s - and the cage won’t break!Now onto solve for the displacement!Your Physics Toolbox
7. Equations of motion (part 1): Playing With Equations
How high should the crane be?Graphs and equations both represent the real worldYou’re interested in the start and end pointsYou have an equation for the velocity - but what about the displacement?See the average velocity on your velocity-time graphTest your equations by imagining them with different numbersCalculate the cage’s displacement!You know how high the crane should be!But now the Dingo needs something more generalA substitution will helpGet rid of the variables you don’t want by making substitutionsContinue making substitutions ...You did it - you derived a useful equation for the cage’s displacement!Check your equation using UnitsCheck your equation by trying out some extreme valuesYour equation checks out!Question Clinic: The “Substitution” QuestionQuestion Clinic: The “Units” or “Dimensional analysis” QuestionThink like a physicist!Your Physics Toolbox
8. Equations of Motion (Part 2): Up, up, and... back down
Previously ...Now ACME has an amazing new cage launcherThe acceleration due to gravity is constantVelocity and acceleration are in opposite directions, so they have opposite signsYou can use one graph to work out the shapes of the othersIs a graph of your equation the same shape as the graph you sketched?Ready to launch the cage!Your launch velocity of 5.0 m/s is definitely right!Fortunately, ACME has a rocket-powered hovercraft!You can work out a new equation by making a substitution for tMultiply out the parentheses in your equationYou can sort out one of the terms on the right hand side like thisYou have two sets of parentheses multiplied togetherThen you can figure out your second term on the right hand sideWhere you’re at with your new equationYou need to simplify your equation by grouping the termsYou can use your new equation to work out the stopping distanceThere are THREE key equations you can use when there’s constant accelerationYou need to work out the launch velocity that gets the Dingo out of the Grand Canyon!The launch velocity’s right!You need to find another way of doing this problemQuestion Clinic: The “Sketch a graph” or “Match a graph” QuestionQuestion Clinic: The “Symmetry” and “Special points” QuestionsYour Physics Toolbox
9. Triangles, Trig and Trajectories: Going two-dimensional
Camelot - we have a problem!How wide should you make the moat?Looks like a triangle, yeah?A scale drawing can solve problemsPythagoras’ Theorem lets you figure out the sides quicklySketch + shape + equation = Problem solved!You kept them out!But the attackers get smarter!Camelot ... we have ANOTHER problem!Relate your angle to an angle inside the triangleClassify similar triangles by the ratios of their side lengthsSine, cosine and tangent connect the sides and angles of a right-angled triangleHow to remember which ratio is which??Calculators have sin(θ), cos(θ) and tan(θ) tables built inBack at the castle, everyone’s depending on you!You can know everything! *Does your answer SUCK?Uh oh. Gravity...The cannonball’s velocity and acceleration vectors point in different directionsGravity accelerates everything downwards at 9.8 m/s2The horizontal component of the velocity can’t change once you’ve let goThe horizontal component of a projectile’s velocity is constantThe same method solves both problemsQuestion Clinic: The “Projectile” QuestionAnd so they ran away ...Question Clinic: The “Missing steps” QuestionYour Physics Toolbox
10. Momentum Conservation: What Newton Did
The pirates be havin’ a spot o’ bother with a ghost ship ...What does the maximum range depend on?Firing at 45° maximizes your rangeYou can’t do everything that’s theoretically possible - you need to be practical tooSieges-R-Us has a new stone cannonball, which they claim will increase the range!Massive things are more difficult to start offMassive things are more difficult to stopNewton’s First LawMass mattersA stone cannonball has a smaller mass - so it has a larger velocity. But how much larger?Here’s your lab equipmentHow are force, mass and velocity related?Vary only one thing at a time in your experimentMass x velocity - momentum - is conservedA greater force acting over the same amount of time gives a greater change in momentumWrite momentum conservation as an equationMomentum conservation and Newton’s Third Law are equivalentYou’ve calculated the stone cannonball’s velocity......but you want the new range!Use proportion to work out the new rangeYou solved the pirates’ problem!Question Clinic: The “Proportion” Question (often multiple choice)Your Physics Toolbox
11. Weight and the normal force: Forces for courses
WeightBotchers are at it again!Is it really possible to lose weight instantly?!Scales work by compressing or stretching a springMass is a measurement of “stuff”Weight is a forceThe relationship between force and mass involves momentumIf the object’s mass is constant, Fnet = maThe scales measure the support forceNow you can debunk the machine!The machine reduces the support forceForce pairs help you check your workYou debunked WeightBotchers!But WeightBotchers are back!A surface can only exert a force perpendicular (or normal) to itWhen you slide downhill, there’s zero perpendicular accelerationUse parallel and perpendicular force components to deal with a slopeAnother fake busted!Question Clinic: The “Free body diagram” QuestionQuestion Clinic: The “Free body diagram” QuestionYour Physics Toolbox
12. Using forces, momentum, friction and impulse: Getting on with it
It’s ... SimFootball!Momentum is conserved in a collisionBut the collision might be at an angleA triangle with no right angles is awkwardUse component vectors to create some right-angled trianglesThe programmer includes 2D momentum conservation ......but the players keep on sliding for ever!In real life, the force of friction is presentFriction depends on the types of surfaces that are interactingFriction depends on the normal forceBe careful when you calculate the normal forceYou’re ready to use friction in the game!Including friction stops the players from sliding forever!The sliding players are fine - but the tire drag is causing problemsUsing components for the tire drag works!Question Clinic: The “Friction” QuestionHow does kicking a football work?FΔt is called impulseThe game’s great - but there’s just been a spec change!The strength of the moon’s gravitational field is lower then the Earth’sFor added realism, sometimes the players should slipYou can change only direction horizontally on a flat surface because of frictionThe game is brilliant, and going to X-Force rocks!Newton’s Laws give you awesome powersYour Physics Toolbox
13. Torque and Work: Getting a lift
Half the kingdom to anyone who can lift the sword in the stone ...Can physics help you to lift a heavy object?Use a lever to turn a small force into a larger forceDo an experiment to determine where to position the fulcrumZero net torque causes the lever to balanceUse torque to lift the sword and the stone!Question Clinic: The “Two equations, two unknowns” QuestionSo you lift the sword and stone with the lever ......but they don’t go high enough!You can’t get something for nothingWhen you move an object against a force, you’re doing workThe work you need to do a job = force x displacementWhich method involves the least amount of work?Work has units of JoulesEnergy is the capacity that something has to do workLifting stones is like transferring energy from one store to anotherEnergy conservation helps you to solve problems with differences in heightOne of our stackable stones is missing ...Will energy conservation save the day?You need to do work against friction as well as against gravityDoing work against friction increases internal energyHeating increases internal energyIt’s impossible to be 100% efficientYour Physics Toolbox
14. Energy Conservation: Making your life easier
The ultimate bobsled experienceForces and component vectors solve the first part ......but the second part doesn’t have a uniform slopeA moving object has kinetic energyThe kinetic energy is related to the velocityCalculate the velocity using energy conservation and the change in heightYou’ve used energy conservation to solve the second partIn the third part, you have to apply a force to stop a moving objectPutting on the brake does work on the trackDoing work against friction increases the internal energyEnergy conservation helps you to do complicated problems in a simpler wayThere’s a practical difference between momentum and kinetic energyQuestion Clinic: The “Show that” QuestionQuestion Clinic: The “Energy transfer” QuestionAfter the roaring success of SimFootball, it’s time for SimPoolReusing the old code makes the pool balls stick together!Momentum conservation will solve an inelastic collision problemYou need a second equation for an elastic collisionEnergy conservation gives you the second equation that you need!Factoring involves putting in parenthesesYou can deal with elastic collisions nowIn an elastic collision, the relative velocity reversesThe pool ball collisions work!There’s a gravity-defying trick shot to sort out ...Where is the problem with the programmer’s reasoning?The initial collision is inelastic - so mechanical energy isn’t conservedUse momentum conservation for the inelastic partQuestion Clinic: The “Ballistic pendulum” QuestionYour Physics Toolbox
15. Tension, Pulleys and Problem Solving: Changing direction
It’s a bird... it’s plane......no, it’s... a guy on a skateboard?!Always look for something familiarMichael and the stack accelerate at the same rateUse tension to tackle the problemLook at the big picture as well as the partsBut the day before the competition ...Using energy conservation is simpler than using forcesThere goes that skateboard...Your Physics Toolbox
16. Circular Motion (Part 1): From α to ω
Limber up for the Kentucky Hamster DerbyYou can revolutionize the hamsters’ trainingThinking through different approaches helpsA circle’s radius and circumference are linked by ΠConvert from linear distance to revolutionsConvert the linear speeds into HertzSo you set up the machine ......but the wheel turns too slowly!Try some numbers to work out how things relate to each otherWhat if you set the motor to ‘1.0’?What if the wheel goes at 1.0 Hz?The units on the motor are radians per secondConvert frequency to angular frequencyThe hamster trainer is complete!A couple of weeks later ...You can increase the (linear) speed by increasing the wheel’s radiusQuestion Clinic: The “Angular quantities” QuestionYour Physics Toolbox
17. Circular Motion (Part 2) Staying on track
Houston ... we have a problemWhen you’re in freefall, objects appear to float beside youWhat’s the astronaut missing, compared to when he’s on Earth?Can you mimic the contact force you feel on Earth?Accelerating the space station allows you to experience a contact forceYou can only go in a circle because of a centripetal forceCentripetal force acts towards the center of the circleThe astronaut experiences a contact force when you rotate the space stationWhat affects the size of centripetal force?Spot the equation for the centripetal accelerationGive the astronauts a centripetal forceThe astronauts want as much floor space as possibleHere, the floor space is the area of a cylinder’s curved surfaceIf you work out the volume, you can calculate the astronauts’ floor spaceLet’s test the space station...Can’t cope with rotationApple falls straight while space station rotatesHead and feet at different radiiFewer uncomfortable things happen with the 100 m radius space stationYou’ve sorted out the space station design!Question Clinic: The “Centripetal force” QuestionBack to the track!The bobsled needs to turn a cornerAngling the track gives the normal force a horizontal componentWhen you slide downhill, there’s no perpendicular accelerationWhen you turn a corner, there’s no vertical accelerationHow to deal with an object on a slopeBanking the track works ......but now they want it to loop-the-loop!The “support force” (normal force or tension force) required for a vertical circle variesAny force that acts towards the center of the circle can provide a centripetal forceHow fast does the bobsled need to go?Question Clinic: The “Banked curve” QuestionQuestion Clinic: The “Vertical circle” QuestionYour Physics Toolbox
18. Gravitation and Orbits: Getting away from it all
Party planners, a big event, and lots of cheeseWhat length should the cocktail sticks be?The cheese globe is a sphereThe surface area of the sphere is the same as the surface area of the cheeseLet there be cheese......but there are gaps in the globe!The party’s on!To infinity - and beyond!Earth’s gravitational force on you becomes weaker as you go further awayGravitation is an inverse square lawNow you can calculate the force on the spaceship at any distance from the EarthThe potential energy is the area under the force-displacement graphIf U = 0 at infinity, the equation works for any star or planetUse energy conservation to calculate the astronaut’s escape velocityWe need to keep up with our astronautThe centripetal force is provided by gravityWith the comms satellites in place, it’s Pluto (and beyond)Question Clinic: The “gravitational force = centripetal force” QuestionYour Physics Toolbox
19. Oscillations (Part 1): Round and round
Welcome to the fair!Reproduce the duck on the displayThe screen for the game is TWO-DIMENSIONALSo we know what the duck does......but where exactly is the duck?Any time you’re dealing with a component vector, try to spot a right-angled triangleLet’s show Jane the displayThe second player sees the x-component of the duck’s displacementWe need a wider definition of cosine, toosine and cosine are related to each otherLet the games begin!Jane’s got another request: What’s the duck’s velocity from each player’s point of view?Get the shape of the velocity-time graph from the slope of the displacement-time graphThe game is complete!Your Physics Toolbox
20. Oscillations (Part 2): Springs ‘n’ swings
Get rocking, not talkingThe plant rocker needs to work for three different masses of plantA spring will produce regular oscillationsDisplacement from equilibrium and strength of spring affect the forceA mass on a spring moves like a side-on view of circular motionA mass on a spring moves with simple harmonic motionSimple harmonic motion is sinusoidalWork out constants by comparing a situation-specific equation with a standard equationLook at the amplitudeLook at the argument of the cosineQuestion Clinic: The “This equation is like that one” QuestionYou rock! Or at least Anne’s plants doBut Anne forgot to mention someting ...The plants rock - and you rule!But now the plant rocker’s frequency has changed ...The frequency of a horizontal spring depends on the massWill using a vertical spring make a difference?A pendulum swings with simple harmonic motionWhat does the frequency of a pendulum depend on?The pendulum design works!Question Clinic: The “Vertical spring” QuestionQuestion Clinic: The “How does this depend on that” QuestionYour Physics Toolbox
21. Think Like a Physicist: It’s the final chapter
You’ve come a long way!Now you can finish off the globeThe round-trip looks like simple harmonic motionBut what time does the round-trip take?You can treat the Earth like a sphere and a shellThe net force from the shell is zeroThe force is proportional to the displacement, so your trip is SHMQuestion Clinic: The “Equation you’ve never seen before” QuestionYou know your average speed - but what’s your top speed?Circular motion from side on looks like simple harmonic motionYou can do (just about) anything!
A. Leftovers: The top 6 things (that we didn’t cover before, but are covering now)
#1 Equation of a straight line graph, y = mx + c#2 Displacement is the area under the velocity-time graph#3 Torque on a bridge#4 Power#5 Lots of practice questions#6 Exam tips
B. Equation Table: Point of Reference
Mechanics equation table
Index
About the Author
Copyright

Overview

Wouldn't it be great if there were a physics book that showed you how things work instead of telling you how? Finally, with Head First Physics, there is. This comprehensive book takes the stress out of learning mechanics and practical physics by providing a fun and engaging experience, especially for students who "just don't get it."

Head First Physics offers a format that's rich in visuals and full of activities, including pictures, illustrations, puzzles, stories, and quizzes -- a mixed-media style proven to stimulate learning and retention. One look will convince you: This isn't mere theory, this is physics brought to life through real-world scenarios, simple experiments, and hypothetical projects. Head First Physics is perfect for anyone who's intrigued by how things work in the natural world.

You'll quickly discover that physics isn't a dry subject. It's all about the world we live in, encompassing everything from falling objects and speeding cars, to conservation of energy and gravity and weightlessness, and orbital behavior. This book:

Helps you think like a physicist so you can understand why things really work the way they do
Gives you relevant examples so you can fully grasp the principles before moving on to more complex concepts
Designed to be used as a supplement study guide for the College Board's Advanced Placement Physics B Exam
Introduces principles for the purpose of solving real-world problems, not memorization
Teaches you how to measure, observe, calculate -- and yes -- how to do the math
Covers scientific notation, SI units, vectors, motion, momentum conservation, Newton's Laws, energy conservation, weight and mass, gravitation and orbits, circular motion and simple harmonic motion, and much more

If "Myth Busters" and other TV programs make you curious about our physical world -- or if you're a student forced to take a physics course -- now you can pursue the subject without the dread of boredom or the fear that it will be over your head. Head First Physics comes to rescue with an innovative, engaging, and inspirational way to learn physics!

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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