Book description
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 mixedmedia style proven to stimulate learning and retention. One look will convince you: This isn't mere theory, this is physics brought to life through realworld 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 realworld 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!
Table of contents
 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
 Acknowledgments

1. Think Like a Physicist: In the beginning ...
 Physics is the world around you
 You can get a feel for what’s happening by being a part of it
 Use your intuition to look for ‘special points’
 The center of the earth is a special point
 Ask yourself “What am I ALREADY doing as I reach the special point?”
 Where you’re at  and what happens next?
 Now put it all together
 Your 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 case
 When the myPod case comes back from the factory...
 ...it’s waaay too big!
 There aren’t any UNITS on the blueprint
 You’ll use SI units in this book (and in your class)
 You use conversion factors to change units
 You can write a conversion factor as a fraction
 Now you can use the conversion factor to update the blueprint
 You 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 usable
 How many digits of your measurements look significant?
 Generally, you should round your answers to three significant digits
 Is 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 it
 The error on your original measurements should propagate through to your converted blueprint
 Right! 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 digits
 Your Physics Toolbox

3. Scientific Notation, Area, and Volume: All numbers great and small
 A messy college dorm room
 So how long before things go really bad?
 Power notation helps you multiply by the same number over and over
 Your calculator displays big numbers using scientific notation
 Scientific notation uses powers of 10 to write down long numbers
 Scientific notation helps you with small numbers as well
 You’ll often need to work with area or volume
 Look up facts in a book (or table of information)
 Prefixes help with numbers outside your comfort zone
 Scientific notation helps you to do calculations with large and small numbers
 The guys have it all worked out
 200,000,000 meters cubed bugs after only 16 hours is totally the wrong size of answer!
 Be careful converting units of area or volume
 So the bugs won’t take over ... unless the guys sleep in!
 Question Clinic: The “Converting units of area or volume” Question
 Your 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 time
 If you write the delivery time as an equation, you can see what’s going on
 Use variables to keep your equation general
 You need to work out Alex’s cycling time
 When 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 speed
 Write down your results... in a table
 Use the table of distances and times to work out Alex’s speed
 Random errors mean that results will be spread out
 A graph is the best way of taking an average of ALL your results
 Use a graph to show Alex’s time for ANY distance
 The line on the graph is your best estimate for how long Alex takes to cycle ANY distance
 You can see Alex’s speed from the steepness of the distancetime graph
 Alex’s speed is the slope of the distancetime graph
 Now work out Alex’s average speed from your graph
 You need an equation for Alex’s time to give to the web guys
 Rearrange the equation to say “Δ time = something”
 Use your equation to work out the time it takes Alex to reach each house
 So 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 equation
 The Break Neck website goes live, and the customers love it!
 A few weeks later, you hear from Break Neck again
 A graph lets you see the difference the stop lights made
 The stop lights change Alex’s average speed
 Add 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 Party
 Question Clinic: The “Did you do what they asked you” Question
 Your Physics Toolbox

5. Dealing with Directions: Vectors
 The treasure hunt
 Displacement is different from distance
 Distance is a scalar; displacement is a vector
 You can represent vectors using arrows
 You found the next clue...
 You can add vectors in any order
 Well done  you’ve found the third clue!
 Question Clinic: The “Wheat from the chaff” Question
 Angles measure rotations
 Now you can get on with clue 3!
 If you can’t deal with something big, break it down into smaller parts
 You move onto the fourth clue...
 Velocity is the ‘vector version’ of speed
 Write units using shorthand
 So, 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 boat
 It takes the boat time to accelerate from a standing start
 How do you deal with acceleration?
 So it’s back to the boat ...
 Vector, Angle, Velocity, Acceleration = WINNER!!!
 Your Physics Toolbox
 Question Clinic: The “Design an experiment” Question

6. Displacement, Velocity, and Acceleration: What’s going on?
 Just another day in the desert ...
 ...and another DingoEmu moment!
 How can you use what you know?
 The cage accelerates as it falls
 ‘ Vectorize’ your equation
 You want an instantaneous velocity, not an average velocity
 You already know how to calculate the slope of a straight line...
 A point on a curved line has the same slope as its tangent
 The slope of something’s velocitytime graph lets you work out its acceleration
 Work out the units of acceleration
 Success! 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 world
 You’re interested in the start and end points
 You have an equation for the velocity  but what about the displacement?
 See the average velocity on your velocitytime graph
 Test your equations by imagining them with different numbers
 Calculate the cage’s displacement!
 You know how high the crane should be!
 But now the Dingo needs something more general
 A substitution will help
 Get rid of the variables you don’t want by making substitutions
 Continue making substitutions ...
 You did it  you derived a useful equation for the cage’s displacement!
 Check your equation using Units
 Check your equation by trying out some extreme values
 Your equation checks out!
 Question Clinic: The “Substitution” Question
 Question Clinic: The “Units” or “Dimensional analysis” Question
 Think 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 launcher
 The acceleration due to gravity is constant
 Velocity and acceleration are in opposite directions, so they have opposite signs
 You can use one graph to work out the shapes of the others
 Is a graph of your equation the same shape as the graph you sketched?
 Ready to launch the cage!
 Fortunately, ACME has a rocketpowered hovercraft!
 You can work out a new equation by making a substitution for t
 Multiply out the parentheses in your equation
 You have two sets of parentheses multiplied together
 Where you’re at with your new equation
 You need to simplify your equation by grouping the terms
 You can use your new equation to work out the stopping distance
 There are THREE key equations you can use when there’s constant acceleration
 You 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 problem
 Question Clinic: The “Sketch a graph” or “Match a graph” Question
 Question Clinic: The “Symmetry” and “Special points” Questions
 Your Physics Toolbox

9. Triangles, Trig and Trajectories: Going twodimensional
 Camelot  we have a problem!
 How wide should you make the moat?
 Looks like a triangle, yeah?
 A scale drawing can solve problems
 Pythagoras’ Theorem lets you figure out the sides quickly
 Sketch + 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 triangle
 Classify similar triangles by the ratios of their side lengths
 Sine, cosine and tangent connect the sides and angles of a rightangled triangle
 How to remember which ratio is which??
 Calculators have sin(θ), cos(θ) and tan(θ) tables built in
 Back 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 directions
 Gravity accelerates everything downwards at 9.8 m/s2
 The horizontal component of the velocity can’t change once you’ve let go
 The horizontal component of a projectile’s velocity is constant
 The same method solves both problems
 Question Clinic: The “Projectile” Question
 And so they ran away ...
 Question Clinic: The “Missing steps” Question
 Your 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 range
 You can’t do everything that’s theoretically possible  you need to be practical too
 SiegesRUs has a new stone cannonball, which they claim will increase the range!
 Massive things are more difficult to start off
 Massive things are more difficult to stop
 Newton’s First Law
 Mass matters
 A stone cannonball has a smaller mass  so it has a larger velocity. But how much larger?
 Here’s your lab equipment
 How are force, mass and velocity related?
 Vary only one thing at a time in your experiment
 Mass x velocity  momentum  is conserved
 A greater force acting over the same amount of time gives a greater change in momentum
 Write momentum conservation as an equation
 Momentum conservation and Newton’s Third Law are equivalent
 You’ve calculated the stone cannonball’s velocity...
 ...but you want the new range!
 Use proportion to work out the new range
 You 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 spring
 Mass is a measurement of “stuff”
 Weight is a force
 The relationship between force and mass involves momentum
 If the object’s mass is constant, Fnet = ma
 The scales measure the support force
 Now you can debunk the machine!
 The machine reduces the support force
 Force pairs help you check your work
 You debunked WeightBotchers!
 But WeightBotchers are back!
 A surface can only exert a force perpendicular (or normal) to it
 When you slide downhill, there’s zero perpendicular acceleration
 Use parallel and perpendicular force components to deal with a slope
 Another fake busted!
 Question Clinic: The “Free body diagram” Question
 Question Clinic: The “Free body diagram” Question
 Your Physics Toolbox

12. Using forces, momentum, friction and impulse: Getting on with it
 It’s ... SimFootball!
 Momentum is conserved in a collision
 But the collision might be at an angle
 A triangle with no right angles is awkward
 Use component vectors to create some rightangled triangles
 The programmer includes 2D momentum conservation ...
 ...but the players keep on sliding for ever!
 In real life, the force of friction is present
 Friction depends on the types of surfaces that are interacting
 Friction depends on the normal force
 Be careful when you calculate the normal force
 You’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 problems
 Using components for the tire drag works!
 Question Clinic: The “Friction” Question
 How does kicking a football work?
 FΔt is called impulse
 The game’s great  but there’s just been a spec change!
 The strength of the moon’s gravitational field is lower then the Earth’s
 For added realism, sometimes the players should slip
 You can change only direction horizontally on a flat surface because of friction
 The game is brilliant, and going to XForce rocks!
 Newton’s Laws give you awesome powers
 Your 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 force
 Do an experiment to determine where to position the fulcrum
 Zero net torque causes the lever to balance
 Use torque to lift the sword and the stone!
 Question Clinic: The “Two equations, two unknowns” Question
 So you lift the sword and stone with the lever ...
 ...but they don’t go high enough!
 You can’t get something for nothing
 When you move an object against a force, you’re doing work
 The work you need to do a job = force x displacement
 Which method involves the least amount of work?
 Work has units of Joules
 Energy is the capacity that something has to do work
 Lifting stones is like transferring energy from one store to another
 Energy conservation helps you to solve problems with differences in height
 One of our stackable stones is missing ...
 Will energy conservation save the day?
 You need to do work against friction as well as against gravity
 Doing work against friction increases internal energy
 Heating increases internal energy
 It’s impossible to be 100% efficient
 Your Physics Toolbox

14. Energy Conservation: Making your life easier
 The ultimate bobsled experience
 Forces and component vectors solve the first part ...
 ...but the second part doesn’t have a uniform slope
 A moving object has kinetic energy
 The kinetic energy is related to the velocity
 Calculate the velocity using energy conservation and the change in height
 You’ve used energy conservation to solve the second part
 In the third part, you have to apply a force to stop a moving object
 Putting on the brake does work on the track
 Doing work against friction increases the internal energy
 Energy conservation helps you to do complicated problems in a simpler way
 There’s a practical difference between momentum and kinetic energy
 Question Clinic: The “Show that” Question
 Question Clinic: The “Energy transfer” Question
 After the roaring success of SimFootball, it’s time for SimPool
 Momentum conservation will solve an inelastic collision problem
 You need a second equation for an elastic collision
 Energy conservation gives you the second equation that you need!
 Factoring involves putting in parentheses
 You can deal with elastic collisions now
 In an elastic collision, the relative velocity reverses
 The pool ball collisions work!
 There’s a gravitydefying trick shot to sort out ...
 Where is the problem with the programmer’s reasoning?
 The initial collision is inelastic  so mechanical energy isn’t conserved
 Use momentum conservation for the inelastic part
 Question Clinic: The “Ballistic pendulum” Question
 Your 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 familiar
 Michael and the stack accelerate at the same rate
 Use tension to tackle the problem
 Look at the big picture as well as the parts
 But the day before the competition ...
 Using energy conservation is simpler than using forces
 There goes that skateboard...
 Your Physics Toolbox

16. Circular Motion (Part 1): From α to ω
 Limber up for the Kentucky Hamster Derby
 You can revolutionize the hamsters’ training
 Thinking through different approaches helps
 A circle’s radius and circumference are linked by Π
 Convert from linear distance to revolutions
 Convert the linear speeds into Hertz
 So you set up the machine ...
 ...but the wheel turns too slowly!
 Try some numbers to work out how things relate to each other
 The units on the motor are radians per second
 Convert frequency to angular frequency
 The hamster trainer is complete!
 A couple of weeks later ...
 You can increase the (linear) speed by increasing the wheel’s radius
 Question Clinic: The “Angular quantities” Question
 Your Physics Toolbox

17. Circular Motion (Part 2) Staying on track
 Houston ... we have a problem
 When you’re in freefall, objects appear to float beside you
 What’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 force
 You can only go in a circle because of a centripetal force
 Centripetal force acts towards the center of the circle
 The astronaut experiences a contact force when you rotate the space station
 What affects the size of centripetal force?
 Spot the equation for the centripetal acceleration
 Give the astronauts a centripetal force
 The astronauts want as much floor space as possible
 Here, the floor space is the area of a cylinder’s curved surface
 If you work out the volume, you can calculate the astronauts’ floor space
 Let’s test the space station...
 Fewer uncomfortable things happen with the 100 m radius space station
 You’ve sorted out the space station design!
 Question Clinic: The “Centripetal force” Question
 Back to the track!
 The bobsled needs to turn a corner
 Angling the track gives the normal force a horizontal component
 When you slide downhill, there’s no perpendicular acceleration
 When you turn a corner, there’s no vertical acceleration
 How to deal with an object on a slope
 Banking the track works ...
 ...but now they want it to looptheloop!
 The “support force” (normal force or tension force) required for a vertical circle varies
 Any force that acts towards the center of the circle can provide a centripetal force
 How fast does the bobsled need to go?
 Question Clinic: The “Banked curve” Question
 Question Clinic: The “Vertical circle” Question
 Your Physics Toolbox

18. Gravitation and Orbits: Getting away from it all
 Party planners, a big event, and lots of cheese
 What length should the cocktail sticks be?
 The cheese globe is a sphere
 The surface area of the sphere is the same as the surface area of the cheese
 Let 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 away
 Gravitation is an inverse square law
 Now you can calculate the force on the spaceship at any distance from the Earth
 The potential energy is the area under the forcedisplacement graph
 If U = 0 at infinity, the equation works for any star or planet
 Use energy conservation to calculate the astronaut’s escape velocity
 We need to keep up with our astronaut
 The centripetal force is provided by gravity
 With the comms satellites in place, it’s Pluto (and beyond)
 Question Clinic: The “gravitational force = centripetal force” Question
 Your Physics Toolbox

19. Oscillations (Part 1): Round and round
 Welcome to the fair!
 Reproduce the duck on the display
 The screen for the game is TWODIMENSIONAL
 So 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 rightangled triangle
 Let’s show Jane the display
 The second player sees the xcomponent of the duck’s displacement
 We need a wider definition of cosine, too
 sine and cosine are related to each other
 Let 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 velocitytime graph from the slope of the displacementtime graph
 The game is complete!
 Your Physics Toolbox

20. Oscillations (Part 2): Springs ‘n’ swings
 Get rocking, not talking
 The plant rocker needs to work for three different masses of plant
 A spring will produce regular oscillations
 Displacement from equilibrium and strength of spring affect the force
 A mass on a spring moves like a sideon view of circular motion
 A mass on a spring moves with simple harmonic motion
 Simple harmonic motion is sinusoidal
 Work out constants by comparing a situationspecific equation with a standard equation
 Question Clinic: The “This equation is like that one” Question
 You rock! Or at least Anne’s plants do
 But 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 mass
 Will using a vertical spring make a difference?
 A pendulum swings with simple harmonic motion
 What does the frequency of a pendulum depend on?
 The pendulum design works!
 Question Clinic: The “Vertical spring” Question
 Question Clinic: The “How does this depend on that” Question
 Your Physics Toolbox

21. Think Like a Physicist: It’s the final chapter
 You’ve come a long way!
 Now you can finish off the globe
 The roundtrip looks like simple harmonic motion
 But what time does the roundtrip take?
 You can treat the Earth like a sphere and a shell
 The net force from the shell is zero
 The force is proportional to the displacement, so your trip is SHM
 Question Clinic: The “Equation you’ve never seen before” Question
 You know your average speed  but what’s your top speed?
 Circular motion from side on looks like simple harmonic motion
 You can do (just about) anything!
 A. Leftovers: The top 6 things (that we didn’t cover before, but are covering now)
 B. Equation Table: Point of Reference
 Index
 About the Author
 Copyright
Product information
 Title: Head First Physics
 Author(s):
 Release date: September 2008
 Publisher(s): O'Reilly Media, Inc.
 ISBN: 9780596102371
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