Everyday Machines
The objects we use every day are full of neat physics: a wedge inside a zipper, a vacuum inside a flask, trapped steam inside a pressure cooker, a refrigerant that moves heat out of your fridge.
Each explainer below takes one everyday machine apart step by step, with a written answer up top. A visual lesson is optional, using available credits or plan allowance and your selected options.
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How does a zipper work?
A zipper works by using a slider to lock together two rows of interlocking teeth. As you pull the slider up, its Y-shaped channel forces the teeth to mesh tightly together; pulling it down wedges them apart again.
How does a thermometer work?
A thermometer works by measuring something that changes predictably with temperature. Old liquid thermometers use a fluid that expands as it warms; digital ones use a sensor whose electrical signal shifts with heat.
How does a gyroscope work?
A gyroscope works on the principle that a rapidly spinning wheel resists changes to the direction of its axis. This stability lets it hold or sense orientation — which is why gyroscopes guide planes, phones, and spacecraft.
Every explainer in this guide · 118
How does a thermos work?
A thermos works by blocking the three ways heat moves, keeping drinks hot or cold for hours. A vacuum between its double walls stops heat conduction and convection, while a shiny reflective lining bounces heat radiation back.
How does a pressure cooker work?
A pressure cooker works by trapping steam in a sealed pot, which raises the pressure and lets water boil hotter than usual. The higher temperature cooks food much faster, because heat penetrates and breaks it down more quickly.
How does a refrigerator work?
A refrigerator works by moving heat from inside to outside, using a fluid (refrigerant) that absorbs heat as it evaporates and releases it as it condenses. It doesn't make cold — it pumps heat away, leaving the inside cooler.
How does a microwave oven work?
A microwave oven works by flooding food with microwaves — a type of electromagnetic wave — that make water molecules vibrate. That rapid jiggling is heat, so the food warms from the inside out, cooking far faster than a conventional oven.
How does a washing machine work?
A washing machine cleans clothes by tumbling or spinning them in water mixed with detergent, using mechanical motion to loosen dirt. It then drains the dirty water and spins fast to fling most of the water back out of the clothes.
How does a vacuum cleaner work?
A vacuum cleaner works by using a fan to create low air pressure inside it, so the higher-pressure air outside rushes in — carrying dust and dirt with it. A filter or bag traps the debris while letting the air pass back out.
How does an elevator work?
An elevator works by using a motor and a counterweight to raise and lower a car along guide rails. Steel cables connect the car over a pulley to a heavy counterweight, so the motor only needs to move the small difference in weight — making lifting efficient.
How does an escalator work?
An escalator works as a continuous loop of linked steps driven by a motor and chain. The steps stay level at the top and bottom for easy boarding, then rise into stairs in between, while the handrail moves at the same speed for support.
How does a thermostat work?
A thermostat works by sensing the room's temperature and switching heating or cooling on or off to keep it near a set target. It is a feedback loop: when the room drifts from the setpoint, the thermostat turns the system on until the temperature returns.
How does a smoke detector work?
A smoke detector works by sensing smoke particles in the air and sounding an alarm. The common 'ionization' type uses a tiny amount of radioactive material to detect smoke, while 'photoelectric' types watch for smoke scattering a beam of light.
How does a fire extinguisher work?
A fire extinguisher works by removing one of the three things a fire needs: heat, fuel, or oxygen. Most spray a substance that smothers the flames or cools them, breaking the chemical reaction of burning so the fire goes out.
How does an airbag work?
An airbag works by detecting a crash in milliseconds and instantly inflating a cushion to stop your body from hitting the hard interior. A sensor triggers a rapid chemical reaction that fills the bag with gas faster than you can blink.
How does a parachute work?
A parachute works by dramatically increasing air resistance to slow a falling person or object safely to the ground. Its wide canopy traps air, creating a large upward drag force that counteracts gravity and lowers the fall to a gentle speed.
How does a pendulum work?
A pendulum works by swinging back and forth under gravity: when you lift it to one side, gravity pulls it back down, and its momentum carries it up the other side. This steady, repeating swing makes it a natural timekeeper.
How does a water filter work?
A water filter cleans water by passing it through one or more barriers that trap or remove contaminants. Different filters target different things — physical sieves catch particles, carbon absorbs chemicals, and fine membranes block microbes.
How does a car engine work?
A petrol car engine works by burning fuel inside cylinders in tiny, rapid explosions. Each explosion pushes a piston, and those pistons turn a crankshaft that ultimately spins the wheels — repeating the four-stroke cycle thousands of times a minute.
How does an electric motor work?
An electric motor works by using electricity to create magnetism, which pushes and pulls to spin a shaft. A current flows through coils inside a magnetic field, and the resulting force turns the motor — converting electrical energy into motion.
How does a generator work?
A generator works by spinning a coil of wire inside a magnetic field, which pushes electrons through the wire and creates an electric current. It's essentially an electric motor run in reverse — turning motion into electricity.
How does a compass work?
A compass works because its lightweight magnetic needle is free to rotate and aligns itself with Earth's magnetic field. One end always points toward magnetic north, giving you a reliable sense of direction anywhere on the planet.
How does a heat pump work?
A heat pump works by moving heat from one place to another instead of generating it, using a refrigerant cycle. In winter it pulls warmth from the outside air into your home; in summer it runs in reverse to pull heat out — efficiently heating and cooling.
How does a glow stick work?
A glow stick works by mixing two chemicals that react to release energy as light, with no heat or flame. Bending the stick breaks an inner glass tube, letting the chemicals combine and glow — a process called chemiluminescence.
How does a metal detector work?
A metal detector works by sending out a magnetic field that creates tiny electric currents in any nearby metal. Those currents make their own field, which the detector senses and announces with a beep — revealing metal hidden underground or in bags.
How does an ATM work?
An ATM works by securely connecting to your bank over a network to verify your card and PIN, then dispensing cash and updating your account. It is essentially a secure, automated teller linked in real time to the banking system.
How does a barcode work?
A barcode works by encoding a number as a pattern of black bars and white spaces of varying widths. A scanner shines light across it, measures the reflected pattern, and decodes it into the digits that identify the product.
How does a camera work?
A camera works by focusing light through a lens onto a sensor (or film) that records the image. The lens bends incoming light to form a sharp picture, and the sensor measures the light's brightness and color at each point to capture the scene.
How does a lock work?
A lock works by using a key to align internal pins or discs so the plug can rotate and release the latch. When the correct key is inserted, the pins line up at the shear line, allowing the cylinder to turn and the door to open.
How does a toilet flush?
A toilet flush works when pressing the handle lifts a rubber flapper, releasing water from the tank into the bowl. This rush of water creates a siphon in the bowl's curved trapway, pulling waste out through the drain until air breaks the siphon and the tank refills.
How does a ballpoint pen work?
A ballpoint pen writes when a tiny metal ball at its tip rolls across paper, picking up ink from a reservoir and depositing it as a thin line. Gravity and capillary action pull the thick, quick-drying ink down to the ball, which rotates freely in its socket.
How do bicycle gears work?
Bicycle gears change the ratio between how fast you pedal and how fast the rear wheel turns. By shifting the chain between differently sized front and rear sprockets, you trade pedal effort for speed or climbing ease.
How does a bicycle stay upright?
A bicycle stays upright because a moving bike steers itself under the rider, turning the front wheel toward any lean. This self-steering, driven by the bike's geometry and mass distribution, keeps the wheels under the center of mass.
How does a sewing machine work?
A sewing machine forms stitches by using a needle to push thread through fabric, where a rotating hook catches it to create a locked loop. The feed dogs then advance the fabric, allowing rapid, consistent stitching.
How does an air conditioner work?
An air conditioner moves heat from inside a room to the outside air using a refrigerant that evaporates and condenses in a continuous loop. It does not create cold; it removes heat, which is why the outdoor unit blows out warm air.
How does a dishwasher work?
A dishwasher cleans dishes by spraying hot water mixed with detergent over them while a pump circulates the water. Sensors and timers control each phase, from pre-rinse to heated drying, so the load comes out clean and mostly dry.
How does a toaster work?
A toaster converts electrical energy into heat inside a chamber, using a bimetallic strip or timer to pop the toast up when it is browned. The glowing wires heat the bread by radiation and convection, while a latch holds the carriage down until the circuit breaks.
How does an electric kettle work?
An electric kettle boils water by passing electric current through a resistive heating element, usually hidden inside the base or under the floor of the kettle. A thermostat switches the current off automatically when steam reaches a bimetallic strip, so the water stops boiling soon after it starts.
How does an induction cooktop work?
An induction cooktop works by generating a rapidly changing magnetic field in a coil beneath the glass, which induces circular electric currents inside the iron or steel base of a compatible pan. Those currents heat the pan directly, and the pan then cooks the food, while the glass stays relatively cool.
How does a ceiling fan work?
A ceiling fan works by using an electric motor to spin angled blades, which push air downward and create a breeze. This moving air speeds up evaporation of sweat on your skin, making you feel cooler even though the air temperature stays the same.
How does a light bulb work?
An incandescent light bulb works by passing electric current through a thin tungsten filament, heating it until it glows. The glass bulb holds a vacuum or inert gas to prevent the filament from burning up.
How does a fluorescent tube light work?
A fluorescent tube light works by using electricity to excite mercury vapor, which emits ultraviolet light that causes a phosphor coating to glow. This process converts electrical energy into visible light far more efficiently than incandescent bulbs.
How does a doorbell work?
A doorbell works by using a push button to complete an electrical circuit, which sends current to a chime or speaker that produces sound. When the button is pressed, the circuit closes, allowing electricity to flow and activate the sound-making component.
How does a mechanical watch work?
A mechanical watch keeps time using a wound spring that releases energy through a train of gears, regulated by a swinging balance wheel. The balance wheel oscillates at a fixed rate, allowing the hands to move in precise increments.
How does a quartz watch work?
A quartz watch keeps time by counting the vibrations of a tiny quartz crystal. An electric circuit makes the crystal vibrate 32,768 times per second, and a microchip divides that frequency down to one pulse per second to drive the hands.
How does a hair dryer work?
A hair dryer pulls room air in with a fan, then pushes that air across electrically heated metal coils before it exits the nozzle. The moving air carries heat to wet hair, raising the water's temperature so it evaporates faster.
How does a clothes iron work?
A clothes iron works by combining heat, moisture, and pressure to relax the fibres in fabric. The heated soleplate transfers thermal energy, while steam and downward force flatten wrinkles, leaving cloth smooth.
How does a water heater work?
A water heater warms cold water by transferring heat from a fuel source or electric element into a tank or directly through a pipe. It stores hot water for later use or heats it instantly on demand.
How does a hydraulic jack work?
A hydraulic jack multiplies a small force into a large lifting force by pushing fluid through two connected pistons of different sizes. Because the fluid pressure is the same everywhere, the larger piston exerts a proportionally larger force.
How do car brakes work?
Car brakes slow a moving vehicle by converting its kinetic energy into heat through friction. When you press the pedal, hydraulic fluid transmits force to brake pads or shoes, which clamp onto spinning metal surfaces and bring the wheels to a stop.
How does a car clutch work?
A car clutch connects the engine to the gearbox by pressing two spinning plates together, allowing power to flow smoothly. Pressing the clutch pedal separates the plates, interrupting power so gears can change without grinding.
How does a gearbox work?
A gearbox uses different-sized toothed wheels to change the speed and turning force (torque) coming from a power source. By engaging different pairs of gears, it can make an output turn faster with less force or slower with more force, while keeping the same power.
How does a siphon work?
A siphon moves liquid from a higher container to a lower one by using gravity and atmospheric pressure to pull the liquid up and over an intermediate high point. The liquid flows because the weight of the falling column on the exit side is greater than the weight of the rising column on the entry side.
How does a hand pump work?
A hand pump works by using a piston and two one-way valves to create a pressure difference that pushes water up a pipe. When you raise the handle, the piston moves up, opening the lower valve and drawing water into the pump chamber.
How does a vending machine work?
A vending machine works when you insert money, make a selection, and the machine's control board verifies payment and sends a signal to a motor that turns a spiral or pushes a product forward until it drops into the delivery bin. Sensors confirm the item fell, and the machine returns change or refunds if the product is stuck.
How does Velcro work?
Velcro works through the interlocking of tiny hooks on one strip and loops on another, creating a temporary bond. When pressed together, the hooks catch the loops, and pulling them apart requires force to break the connection.
How does a stapler work?
A stapler drives a metal staple through paper and folds its legs flat against a metal anvil. This clinching action binds the sheets together without punching a hole through them.
How does a hot air balloon fly?
A hot air balloon flies because heating the air inside its envelope makes that air less dense than the cooler air outside, so the balloon rises. Pilots control altitude by burning propane to heat the air or letting it cool.
How does a ship float?
A ship floats because its hull is shaped to push aside a large volume of water, and the upward buoyant force from the displaced water equals the ship's weight. As long as the ship weighs less than the water it displaces, it stays afloat.
How does a kite fly?
A kite flies because moving air pushes against its tilted surface, creating an upward force called lift that overcomes the kite's weight. The string anchors the kite and lets the flyer adjust its angle to the wind.
How does a boomerang come back?
A boomerang returns because its two arms spin like wings, creating uneven lift that makes it curve through the air. When thrown correctly, this curved path forms a loop that brings it back near the thrower.
How does a spinning top stay up?
A spinning top stays upright because its rapid rotation resists changes to its orientation through a property called angular momentum. As friction slows the spin, this stabilizing effect weakens and the top eventually topples.
How does a sailboat sail into the wind?
A sailboat sails into the wind by pointing its bow about 45 degrees off the wind direction and using the sails as airfoils to generate lift, which pulls the boat forward. The keel or centerboard prevents sideways drift, so the forward component of the lift moves the boat ahead.
How does a lightning rod work?
A lightning rod works by offering a low-resistance path that safely conducts lightning current to the ground. Its sharp tip also ionizes nearby air, making it a preferred strike point that protects the structure.
How does an electrical fuse work?
An electrical fuse is a deliberate weak link in a circuit that melts when too much current flows, breaking the circuit. This prevents overheating and fires by sacrificing a cheap metal strip instead of the wiring or appliance.
How does a circuit breaker work?
A circuit breaker is an automatic switch that trips open when current in a circuit rises above a safe level. It cuts the flow of electricity before overheating wires can start a fire, and can be reset by hand once the fault is fixed.
How does a transformer work?
A transformer changes alternating current from one voltage to another using electromagnetic induction between two coils. An alternating current in the primary coil creates a changing magnetic field that induces a voltage in the secondary coil, with the ratio of turns determining the voltage change.
How does a power inverter work?
A power inverter converts direct current (DC) into alternating current (AC) by rapidly switching the DC input on and off to create a changing voltage. This switching action produces a waveform that can be stepped up or down to match the voltage and frequency needed by AC-powered devices.
How does a power bank work?
A power bank stores electrical energy in a rechargeable battery and releases it through a circuit that converts the battery's voltage to a USB-friendly level. When you plug in a device, the power bank's output port delivers current to charge the device's battery.
How does a TV remote control work?
A TV remote control sends invisible pulses of infrared light to a sensor on the television. Each button press produces a unique coded pattern of light flashes that the TV decodes into a specific command.
How does a projector work?
A projector works by shining a bright lamp through or off a small image chip, then magnifying that image onto a wall or screen with a lens. The chip creates the picture pixel by pixel, and the lens throws it far away so everyone in the room sees the same large view.
How does an inkjet printer work?
An inkjet printer works by ejecting tiny droplets of liquid ink onto paper, building an image from thousands of precisely placed dots. A moving print head scans across the page while a controller decides exactly where each droplet lands.
How does a computer keyboard work?
A computer keyboard works by using a grid of electrical switches under the keys; pressing a key closes a specific switch, and a small microcontroller detects which row and column intersect to identify the character. That code is sent to the computer, which translates it into the letter, number or symbol you see on screen.
How does a computer mouse work?
A computer mouse converts the physical movement of your hand into digital signals that control a cursor on screen. It tracks motion in two dimensions, detects button clicks and scroll wheel turns, and sends this data to the computer for processing.
How does a carbon monoxide detector work?
A carbon monoxide detector uses a chemical or electronic sensor that reacts with CO gas, producing a measurable change in electrical current or resistance. When CO reaches a set threshold, the device sounds an alarm to warn of dangerous exposure.
How does a gas stove work?
A gas stove burns a controlled mixture of natural gas or propane and air to produce a steady blue flame that heats food. Turning the knob opens a valve, releases gas, and triggers a spark or pilot light to ignite it.
How does a digital weighing scale work?
A digital weighing scale measures weight by converting the mechanical force of an object into an electrical signal. It uses a load cell that deforms slightly under the object's weight, producing a voltage change that a microcontroller converts into a digital weight reading.
How does an air purifier work?
An air purifier works by pulling room air through filters with a fan, trapping particles and sometimes adsorbing gases or killing microbes. Clean air is then pushed back into the room, gradually reducing airborne pollutants.
How does an electric heater work?
An electric heater works by passing an electric current through a resistive wire, which converts electrical energy into heat that is then transferred to the surrounding air. This heat warms the room through a combination of convection and radiation.
How does a garage door opener work?
A garage door opener works by using a motor to pull the door along a track or turn the torsion-spring shaft, controlled by a remote signal. The motor engages a trolley or chain that moves the door up or down, with safety sensors stopping it if an object is detected.
How does a motion sensor work?
A motion sensor works either by sensing shifts in infrared heat from warm bodies (passive sensors, the most common) or by sending out microwaves or ultrasound and detecting changes in the reflected energy when an object moves. When the received signal changes, the sensor's circuit triggers an output, like turning on a light or sounding an alarm.
How does a smart lock work?
A smart lock replaces a keyed cylinder with a motorised bolt that a small computer unlocks after checking a credential such as a code, phone or fingerprint. The lock stores and verifies that credential locally or over a wireless link, then drives the bolt open, often relocking automatically after a set time.
How does a dehumidifier work?
A dehumidifier works by cooling air below its dew point so water vapour condenses into liquid, then reheating the air and collecting the water in a tank. A fan pulls room air across cold coils, where moisture turns to droplets that drip away, leaving drier air.
How does a humidifier work?
A humidifier adds water vapour to indoor air by turning liquid water into fine droplets or vapour that mix with the air. This raises relative humidity, which can ease dry skin, sore throats and static, but the mechanism differs by type.
How does a security camera work?
A security camera works by focusing light through a lens onto an image sensor that converts the light into electrical signals, which are then processed into digital video. The camera compresses and transmits this video over a network or cable to a recorder or cloud service for storage and viewing.
How does an evaporative cooler work?
An evaporative cooler works by pulling hot, dry air through a water-soaked pad, where water absorbs heat and evaporates into the air. This adds moisture and lowers the air temperature, so the fan delivers cooler, more humid air into the room.
How does a water softener work?
A water softener removes calcium and magnesium ions from hard water by swapping them for sodium ions through a process called ion exchange. This prevents scale buildup in pipes and appliances, making soap lather more easily and extending the life of plumbing.
How does a septic tank work?
A septic tank works by holding household wastewater long enough for heavy solids to settle as sludge and lighter fats to float as scum, while bacteria break down the organic matter. The clarified liquid flows out into a drainfield, where soil microbes and filtration remove remaining pollutants.
How does a light switch work?
A light switch works by physically opening or closing a gap in an electrical circuit, allowing current to flow to a light fixture when closed and stopping it when open. The switch itself does not generate or consume electricity; it simply controls whether the circuit is complete.
How does a dimmer switch work?
A dimmer switch controls brightness by rapidly switching the lamp on and off many times per second, so the lamp receives only a fraction of the full power. The longer the off periods relative to the on periods, the dimmer the light appears.
How do fire sprinklers work?
Fire sprinklers work by using heat to melt or break a heat-sensitive element in each sprinkler head, releasing pressurised water only from the heads directly above a fire. Most sprinklers in a building stay closed, so water is concentrated where it is needed.
How does a fountain pen work?
A fountain pen works by letting gravity and capillary action pull ink from a reservoir through a feed to a slit nib, where it flows onto paper. Air entering the reservoir replaces the ink, keeping the internal pressure balanced so writing continues smoothly.
How does a photocopier work?
A photocopier works by using static electricity to attract toner powder onto a light-sensitive drum, then transferring that powder to paper and fusing it with heat. The process repeats for each copy, with the drum recharged and cleaned for the next page.
How does a laser printer work?
A laser printer works by using a laser beam to draw an electrostatic image on a rotating drum, which then attracts toner particles. The toner is transferred and fused onto paper by heat and pressure to create the final print.
How does a calculator work?
A calculator converts each key press into a binary number, then uses a pre-built logic circuit or a stored program to perform arithmetic on those numbers. The result is decoded and shown on the display as decimal digits.
How does a sundial work?
A sundial works because Earth's rotation makes the Sun appear to move across the sky, so a fixed gnomon casts a shadow that sweeps across a marked plate. The shadow's position and length indicate the time of day and the season.
How does an hourglass work?
An hourglass works because sand flows through a narrow opening at a constant rate, driven by gravity. The time it takes for all the sand to fall depends on the amount of sand and the size of the opening, not on how much sand remains above.
How does a thermal camera work?
A thermal camera works by detecting infrared radiation that warm objects emit, then converting that invisible energy into a visible image. Unlike ordinary cameras that capture reflected light, it measures temperature differences across a scene.
How does night vision work?
Night vision works by either amplifying tiny amounts of available light or by detecting infrared radiation that human eyes cannot see. Image-intensifier tubes multiply existing photons, while thermal cameras map heat emitted by objects to create a visible image.
How does a lie detector work?
A lie detector, or polygraph, does not detect lies directly; it measures physiological stress responses such as heart rate, blood pressure, breathing, and skin sweating while a person answers questions. The operator compares reactions to relevant questions against control questions to infer whether the person is being deceptive.
How does a breathalyzer work?
A breathalyzer estimates blood alcohol concentration by measuring ethanol vapour in a breath sample, because alcohol in the blood equilibrates with air in the lungs. Most police devices use a fuel cell or infrared sensor that converts ethanol concentration into a numeric reading.
How does a clothes dryer work?
A clothes dryer works by tumbling wet clothes in a rotating drum while heated air absorbs moisture and is vented away. The combination of heat, airflow, and motion evaporates water from the fabric and carries it out of the machine.
How does a robot vacuum work?
A robot vacuum works by using sensors to map a room and detect obstacles, then a processor plans a cleaning path and controls motors to drive wheels and spin brushes and a fan to lift dirt into a bin.
How do ball bearings work?
Ball bearings reduce friction by placing smooth hardened spheres between two moving surfaces, so those surfaces roll over the balls instead of sliding against each other. The balls roll with very little resistance, and a cage keeps them evenly spaced while lubricant protects the metal.
How do hydraulics work?
Hydraulics works by using a confined liquid to transmit pressure equally in all directions, so a small force on a small piston creates a larger force on a larger piston. Because the liquid is nearly incompressible, the pressure is transmitted undiminished through the system.
How does a crane lift heavy loads?
A crane lifts heavy loads by using a jib or boom to position a hoist, while counterweights and a stable base prevent tipping. The hoist rope winds around a pulley system, and the load's weight is balanced by the crane's structural design and mechanical advantage.
How does a roller coaster work?
A roller coaster works by converting potential energy at the top of a hill into kinetic energy as it descends, then using that energy to climb the next hill. Throughout the ride, the track's shape and the train's speed create changing forces that push riders against their seats or lift them up.
How does a guitar make sound?
A guitar makes sound when a plucked string vibrates and transfers energy through the bridge to the soundboard, which moves air to create pressure waves. The body and air cavity amplify and shape these waves into the notes you hear.
How does a piano work?
A piano makes sound when a pressed key sends a felt hammer to strike a tuned steel string, and a felt damper lifts so the string can vibrate. The vibrating string's energy passes through a bridge to a large wooden soundboard, which moves air and turns a faint string tone into audible sound.
How does an amplifier work?
An amplifier works by using a small input signal to control a larger flow of energy from a power source, copying the input's shape at a higher power. This process, called gain, makes weak signals strong enough to drive speakers, antennas, or other outputs.
How do headphones work?
Headphones convert electrical audio signals into sound waves using a diaphragm driven by an electromagnet or piezoelectric element. The diaphragm's vibrations push air, creating pressure waves that the ear interprets as sound.
How do polarized sunglasses work?
Polarized sunglasses block light waves that vibrate in one particular direction, cutting the glare that reflects off flat surfaces. Most glare is horizontally polarized, so a vertical filter in the lens removes it while letting other light through.
How do 3D glasses work?
3D glasses work by showing each eye a slightly different image, so the brain fuses them into a single scene with depth. The two main types are passive polarized glasses used in cinemas and active shutter glasses used in some home TVs.
How does a one-way mirror work?
A one-way mirror works by making one side much dimmer than the other while using a partially reflective glass coating. Light from the bright side passes through to the dark side, but light from the dark side is too weak to be seen through the reflection.
How do suspension bridges work?
A suspension bridge carries its deck on cables that hang in a curve between tall towers and are anchored at both ends. The deck's weight pulls the cables into tension, and that tension passes through the towers into the ground, letting the span cross wide gaps without many supports.
How do skyscrapers stay up?
Skyscrapers stay up because a strong steel skeleton carries the weight down to deep foundations, while a stiff central core and bracing resist wind. Engineers design every beam and column to handle gravity, wind, and earthquakes safely.
How do earthquake-proof buildings work?
Earthquake-resistant buildings absorb and redirect seismic energy so the structure bends without collapsing. Engineers combine a strong but ductile frame, flexible base isolators, and dampers that convert shaking into heat.
How do gears work?
Gears work by locking toothed wheels together so that turning one forces the other to turn, passing motion and force from shaft to shaft. Changing the number of teeth on each wheel trades speed for turning force, and meshing two gears reverses the direction of rotation.
Key ideas behind them
What is a simple machine?
A simple machine is a basic device that makes work easier by changing the size or direction of a force. There are six classic types — the lever, pulley, wheel and axle, inclined plane, wedge, and screw — and almost every complex machine is built from combinations of them.
What is a lever?
A lever is a simple machine made of a stiff bar that pivots around a fixed point called a fulcrum. By pushing down on one end, you can lift a heavy load on the other — trading a longer push for greater lifting force. Seesaws, scissors, and crowbars are all levers.
What is a pulley?
A pulley is a simple machine made of a wheel with a groove that a rope or cable runs over. It lets you change the direction of a force — pulling down to lift something up — and, with multiple pulleys, lift heavy loads with much less effort.
What is an inclined plane?
An inclined plane is a simple machine: a flat surface tilted at an angle, like a ramp. It makes lifting easier by letting you push a load up a gentle slope instead of straight up — trading a longer distance for less force.
What is a wheel and axle?
A wheel and axle is a simple machine made of a large wheel attached to a smaller rod (the axle) that turn together. Applying a small force to the rim of the big wheel produces a much larger turning force at the axle — or lets the axle move things a long way with each turn.
What is friction?
Friction is the force that resists motion when two surfaces rub against each other. It's why a sliding book slows and stops, why we can walk without slipping, and why rubbing your hands makes heat. No surface is perfectly smooth, so friction is everywhere.
What is buoyancy?
Buoyancy is the upward force a fluid exerts on an object placed in it. If that force is greater than the object's weight, it floats; if less, it sinks. It's why ships float and why you feel lighter in water.
What is pressure?
Pressure is the amount of force pushing on a given area. The same force concentrated on a small area creates high pressure (like a sharp knife), while spread over a large area it creates low pressure (like snowshoes). It is measured in pascals (Pa).
What is heat?
Heat is energy that flows from a hotter object to a cooler one because of their temperature difference. It's the transfer of thermal energy — the energy of moving particles — and it always moves from hot to cold until temperatures even out.
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Frequently asked questions
What are the six simple machines?
The lever, wheel and axle, pulley, inclined plane, wedge and screw. Most everyday machines combine several of them — a zipper's slider, for example, works as a pair of wedges.
How does a thermos keep drinks hot and cold?
A vacuum between two walls blocks heat moving by conduction and convection, and shiny inner surfaces reflect radiant heat. Heat has no easy way in or out, so the drink stays near its starting temperature.
Why does a pressure cooker cook faster?
Sealing the pot lets steam pressure build up, which raises water's boiling point to around 120 °C. Food surrounded by hotter water and steam cooks much faster.