Book summary “The physics of everyday things”: summary

Introduction

You wake up, check your smartphone, heat breakfast, and commute to work without thinking about the invisible physical laws making these actions possible. Modern routines rely on fundamental laws of physics operating quietly inside everyday devices, from smartphones and toasters to transit systems and airport scanners. James Kakalios bridges the gap between advanced science and familiar daily experiences in The Physics of Everyday Things.

You discover how familiar gadgets actually work by exploring the science hidden in plain sight. The book follows a chronological daily journey from morning appliances and city commutes to medical offices and airport security checkpoints.

• How do electric toothbrushes charge without metal contacts?
• Why do GPS satellites require Einstein's theory of relativity to locate you?
• How do airport scanners see through your clothes?

1. Clocks, Power, and Morning Appliances

Morning routines rely on physical laws operating inside ordinary devices. A mechanical grandfather clock uses a swinging bob to mark the passage of time.

Morning routines are governed by the conservation of energy, electromagnetic induction, Joule heating, and thermodynamic cycles operating inside household items.

As the pendulum bob swings, potential energy at the peak is converted into kinetic energy at the bottom of the arc. Air resistance slowly robs the pendulum of its total energy, requiring periodic winding.

Clocks and Timekeeping

A pendulum string that takes one second to complete a full oscillation is less than ten inches long. The time to complete a full oscillation does not depend on the mass or the height of the drop.

Smartphones use a quartz crystal oscillator to keep precise time. When quartz crystals are compressed, their atomic structure buckles to create a net electric field. Applying a voltage causes the crystal sides to pull together and oscillate at a natural frequency determined by their size and shape.

Electricity and Power Grids

Electric utility companies generate alternating current by rotating coils of wire between the poles of electromagnets. This process applies Faraday's law of induction.

In the United States, power plant coils rotate sixty times a second. This rotation produces an alternating voltage wave that requires 0.0167 second to complete one cycle of a wall outlet voltage varying at sixty hertz.

Kitchen Technology

An electric toothbrush uses an internal motor spinning at hundreds of revolutions per second. A battery drives direct current through a coil situated in a magnetic field, twisting the coil and using a switching mechanism to maintain rotation. The charger transfers power wirelessly using a solid plastic base containing a transformer.

Some toothbrushes achieve 1.6 million cycles per second through frequency multipliers and piezoelectric crystals.

A toaster utilizes a nichrome wire that heats up past 1,000°F when the circuit is closed. Forcing current through a high-resistance metal alloy wire causes atoms to vibrate violently enough to emit infrared radiation and visible light. This Joule heating raises bread surfaces to approximately 300°F, where sugars and starches undergo browning reactions.

A smartphone playing a podcast converts digital numerical codes into voltages that drive a speaker membrane.

• Rest the phone's speaker on the bottom of a large wooden bowl to enhance and deepen the tone of the sound.

Refrigeration and Thermodynamics

Modern refrigerators operate as heat engines run in reverse. An electric motor runs a pump that forces a coolant liquid through an expansion valve into a larger volume. The fluid undergoes a phase transition into a vapor by extracting heat from the interior walls.

The compressor then recompresses the gas back into a liquid behind the refrigerator, releasing that absorbed heat outside. Modern refrigerators use tetrafluoroethane as a coolant fluid, replacing older chemicals like Freon. In 2016, 170 nations agreed to reduce the use of hydrofluorocarbons such as tetrafluoroethane.

2. Commuting Physics and Navigation

Driving through the city involves hybrid energy conversion, radio wave communication, relativistic GPS corrections, and the fluid dynamics of traffic.

Automotive Physics

Internal combustion engines offer high energy density from gasoline but poor mileage and emissions. Electric cars are clean but limited by battery energy density. Hybrids use a smaller, highly efficient gas engine for normal driving and an electric motor assist for heavy acceleration or climbing hills.

Driving an electric/gasoline hybrid vehicle that balances both power sources.

GPS and Relativity

Satellites in medium Earth orbit broadcast time and location signals to a GPS receiver, which triangulates position based on transit times. Because satellites move at high velocities and experience weaker gravity than Earth's surface, their atomic clocks are affected by special and general relativity, necessitating precise time adjustments.

Consulting the global positioning system built into the dashboard to find the doctor's office.

There are 32 satellites orbiting Earth in the U.S. system. They operate at roughly 12,600 miles altitude above Earth's surface. Each satellite takes 12 hours to go around the planet, covering 104,000 miles in that time.

Radio Communication Systems

Keyless entry fobs and radio tuners filter out background electromagnetic waves by using resonance to lock onto a specific frequency. Just as a tuning fork vibrates only at its natural frequency when exposed to matching sound waves, radio circuitry creates a large voltage only when detecting an electromagnetic wave at its selected resonant frequency.

Unlocking a car door using the keyless remote control on a key fob.

All automobile remote entry systems in the United States use the standard radio wave frequency of 315 MegaHertz. The receiver also checks a range of 256 twelve-digit numbers in case you press the fob far away.

Electronic toll collection systems like E-ZPass utilize specialized two-way radios operating via electromagnetic waves to instantly process account information. When a car breaks a photodetector light beam in a tollbooth lane, the antenna sends out radio waves. The E-ZPass receiver in the car responds by broadcasting account data, which a computer verifies and charges before the car moves an inch.

Passing an open tollbooth using an E-ZPass device on the windshield instead of paying with cash.

The E-ZPass system uses radio waves operating at 900 MegaHertz. Electromagnetic waves travel at the speed of light in a vacuum, which equals 186,000 miles per second.

Self-parking systems measure distances using radar, lidar, or ultrasonics, relying on physical principles originally developed for military proximity fuses. An onboard transmitter emits a pulse of electromagnetic or sound waves that reflects off obstacles. By calculating the round-trip transit time, the system determines exact distances and maneuvers the vehicle into tight spaces.

Using an automobile's self-parking feature to smoothly maneuver into a tight curbside parking space.

A World War II proximity fuse shell detected its target and triggered an explosion at 75 feet.

Traffic Dynamics

Traffic jams frequently form not due to accidents, but as an intrinsic collective instability caused by driver reaction times and clustering. As car density increases, drivers tend to close gaps rather than maintain spacing. When someone slightly slows down at the front of a cluster, it triggers a backward-propagating avalanche of stopped cars, creating a phantom traffic jam.

Getting stuck in a sudden traffic jam that seems to have popped out of nowhere with no visible cause.

To minimize phantom delays:

• Drive at a steady, uniform speed keeping pace with the average flow of traffic.
• Deliberately avoid shrinking gaps to prevent joining dense clusters of cars.

3. Medical Diagnostics and Digital Screens

Medical visits and digital tablets utilize complex physical phenomena including nuclear magnetic resonance, x-ray scattering, and ultrasonic wave reflections.

Mechanics and Safety

Elevators minimize the energy needed for movement by using a counterweight that balances the average occupancy weight of the car. One end of the elevator cable connects to the car and the other to a counterweight designed to match the car with its average occupancy. When both sides have nearly equal mass, the potential energy increase of one is balanced by the descent of the other, reducing the work required by the electric motor.

An elevator acts like a see-saw where children of equal weight on either end make it much easier to rise and fall. Engineers choose a counterweight size based on 40 percent of the maximum car capacity used as typical average occupancy.

High-speed elevators employ a redundant system of physical safeguards, including multiple cables, rail rollers, governors, and ceramic brake pads. Elevators use four to eight steel cables even though one is strong enough to hold a full car. Vertical rails with rollers keep the car aligned, while accelerometers detect vibrations. Governors engage ratchets if rotation is too fast, and electromagnetically controlled brake clamps coated in hard ceramic material grip the rails without melting from high frictional heating. Certain fast elevator cars reach speeds of 40 miles per hour inside their shafts.

Digital Technology

Smart tablets communicate via radio waves and process streams of digital data representing discrete steps rather than continuous analog variations. Screens consist of millions of pixels controlled by digital code that turns them bright or dark and activates color filters to create high-resolution images. You browse a website on a smart tablet by tapping FLIGHT STATUS and entering a flight number.

Standard tablet screens contain approximately 1,500 pixels along one length and 800 to 1k pixels down the other side. A total threshold of 1 million pixels constitutes a Megapixel.

Traditional and electronic thermometers measure temperature by tracking how thermal expansion or electrical resistance changes uniformly with atomic energy. Glass thermometers work because the liquid expands faster than its glass container due to a difference in their anharmonic terms. You place a glass tube filled with mercury or red-dyed alcohol under the tongue to measure body temperature.

Electronic alternatives use metals or semiconductors whose electrical resistance varies predictably with temperature, or thermocouples that generate a measurable voltage across joined dissimilar metals. Calibrating these devices relies on baseline points including 0°C or 32°F for freezing and 100°C or 212°F for boiling water. Mercury remains a liquid down to -38°F and boils at 674°F, while red-dyed alcohol boils at 173°F.

Medical Diagnostics

X-rays are generated by rapidly decelerating high-energy electrons and create images by scattering off atoms based on their electron density. In an x-ray tube, electrons are accelerated by a positive voltage mesh and then rapidly decelerated by a negative plate, emitting high-energy electromagnetic waves with short wavelengths. Dense atoms with more electrons scatter x-rays effectively, creating bright areas for bones and dark areas for less dense regions or cavities. You take an x-ray of an injured ankle to reveal arthritis or a hairline fracture.

Different atoms contain distinct electron counts that alter scattering properties:

• carbon contains 6 electrons;
• a water molecule contains 10 electrons;
• a calcium atom contains 20 electrons;
• iodine contains 53 electrons;
• barium alone contains 56 electrons;
• barium sulfate contains 104 electrons;
• gold contains 79 electrons;
• lead contains 82 electrons.

Ultrasound imaging uses high-frequency sound waves generated by piezoelectric materials to map internal body density variations through wave reflections. Ultrasound relies on the fact that sound waves change speed depending on the density of the medium. When high-frequency sound waves strike boundaries between tissues with different acoustic properties, part of the wave reflects back. A piezoelectric crystal converts these returning pressure waves into electrical voltages to construct an image.

Medical ultrasound generators typically use 2 to 3 million cycles per second. You guide the needle for a cortisone injection using real-time ultrasound imaging.

Magnetic Resonance Imaging detects the weak magnetic fields of atomic nuclei by measuring the radio wave energy required to flip their orientation. Atomic building blocks possess built-in magnetic fields. When placed inside a powerful electromagnet, nuclear magnets align with or oppose the field. Applying tuned radio wave photons forces these nuclei to flip states, and measuring the relaxation time as they return to their original configuration provides high-contrast data about organic tissue. Albert Einstein recognized in 1905 that light energy is determined by its frequency. You screen patients for tattoos or metallic objects before an MRI due to the powerful magnetic field and potential radio-frequency heating.

4. Airport Security and Data Systems

Navigating airport security and processing digital transactions requires Faraday's law, touch-screen capacitance, millimeter waves, and ion mobility spectrometry.

Credit cards store account information using three distinct physical mechanisms. Raised numbers allow physical carbonless copies using tiny ink-filled spherical particles that break under pressure. The magnetic stripe uses alternating magnetic north poles to store binary data. The RFID chip communicates via radio frequency using near field communication.

Binary counting systems use only two states, 'off' and 'on' or 0 and 1, allowing data storage with simple physical components like magnets or electronic switches. Unlike base-10 counting, base-2 binary doubles each higher denomination. This allows any number or symbol to be represented even when limited to a single physical element for each value, such as a magnetic atom's north pole pointing up or down. Representing the dollar amount 21 in binary as 10101, which equals 16 plus 4 plus 1.

Magnetic stripe readers use Faraday's law of induction to read card data by detecting electrical currents generated by changing magnetic fields. When a card is swiped past a sensor or coil, the alternating north and south poles of the magnetic regions induce an electric current that reverses direction to read as a 1 or circulates in one direction to read as a 0.

Touch Screen Mechanics

Resistive touch screens register physical pressure by forcing two conducting layers together to close an electrical circuit. A transparent conducting plastic top layer is separated by an insulator from a conducting glass bottom layer mapped into a checkerboard grid. Pressing the screen connects the layers, allowing a semiconductor chip to record the active grid location. Using a stylus pen or a gloved finger to sign a credit card purchase on a resistive touch screen.

Capacitive touch screens detect touches by measuring changes in electrical charge storage when a conductive human finger interacts with screen capacitors. The screen consists of a grid of tiny capacitors made of transparent indium tin oxide alloy. When a user touches the screen, their personal capacitance is added to the circuit, altering the stored charge and signaling the processor. Tapping an ATM screen with a finger to withdraw one hundred dollars from a checking account using a four-digit code for ATM PIN.

Total internal reflection traps light inside a denser medium when the incidence angle exceeds a critical threshold, enabling fiber optics and infrared touch screens. When light travels from a slower, high refractive index medium to a faster, lower index medium at a large enough angle, it cannot escape and reflects completely off the interface like a mirror. An infrared touch screen where touching the top glass plate disturbs the totally internally reflected light beams, allowing sensors to track the touch coordinates.

Security Screening Physics

Airport walk-through metal detectors pulse an electric current through coils to create a magnetic field and measure the induced back-current created by metallic objects. When the current is abruptly turned off, the collapsing magnetic field induces a temporary current in the coil. Metallic objects passing through act momentarily as an antenna, altering the magnitude of the induced current as the detector pulses the current a hundred times a second. A TSA PreCheck detector being set off by a passenger's wristwatch.

Full-body airport scanners use millimeter-wave backscattering to image objects hidden beneath clothing without harming the human body. Microwaves pass easily through clothing fibers because their wavelength is much larger than the fibers, but they reflect off denser human skin and contraband items, producing backscattered waves that detectors map into an image. A passenger stands with elbows bent and arms raised in a millimeter-wave full-body scanner with a wavelength of roughly 1 millimeter, or about 0.04 inch, which is over ten times the diameter of an average human hair.

TSA x-ray baggage scanners use transmission mode and solid-state semiconductor detectors to differentiate organic materials from metals based on electron density. X-rays pass through luggage onto semiconductor detector plates divided into pixels. Atoms with more electrons scatter x-rays differently. Systems use high- and low-energy x-rays with metal filters to isolate organic explosives from steel objects, noting that a carbon atom has six electrons while aluminum has thirteen electrons per atom. A TSA agent stops and reverses the conveyor belt after noticing an unclear item in a passenger's carry-on bag.

Explosive-trace detectors use ion mobility spectrometry to identify explosive chemical residues by racing vaporized molecules through a charged cylinder. A paper disc wiped over luggage is heated to vaporize residues. Molecules are stripped of an electron to gain a net positive charge of plus one, and a negative voltage pulls them down a cylinder. Their travel time distinguishes them based on mass and air drag, capturing about a milligram of material transferred from fingerprints. A TSA agent wipes the outside of a bag with a small white paper disc and places it into an explosive-trace detector.

10 Key Ideas

1. A pendulum string that takes one second to complete a full oscillation is less than ten inches long, and its time to complete a full oscillation does not depend on the mass or the height of the drop.
2. Electric utility companies generate alternating current by rotating coils of wire between the poles of electromagnets using Faraday's law of induction.
3. Modern refrigerators operate as heat engines run in reverse where an electric motor runs a pump that forces a coolant liquid through an expansion valve into a larger volume.
4. Because satellites move at high velocities and experience weaker gravity than Earth's surface, their atomic clocks are affected by special and general relativity, necessitating precise time adjustments.
5. Traffic jams frequently form not due to accidents, but as an intrinsic collective instability caused by driver reaction times and clustering.
6. Elevators minimize the energy needed for movement by using a counterweight that balances the average occupancy weight of the car.
7. Magnetic Resonance Imaging detects the weak magnetic fields of atomic nuclei by measuring the radio wave energy required to flip their orientation.
8. The magnetic stripe on credit cards uses alternating magnetic north poles to store binary data.
9. Full-body airport scanners use millimeter-wave backscattering to image objects hidden beneath clothing without harming the human body.
10. Explosive-trace detectors use ion mobility spectrometry to identify explosive chemical residues by racing vaporized molecules through a charged cylinder.