Head First Physics
A learner's companion to mechanics and practical physics (AP Physics B  Advanced Placement)
Publisher: O'Reilly Media
Release Date: June 2009
Pages: 942
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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

Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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


Chapter 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!


Appendix 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 velocitytime graph

#3 Torque on a bridge

#4 Power

#5 Lots of practice questions

#6 Exam tips


Appendix Equation Table: Point of Reference

Mechanics equation table
