Physics

Puzzles

• actual.infinityGive one valid counter-example to "everything is finite": a piece of evidence that the infinite is actually... New
• airplane.liftIs Bernoulli's principle the explanation of how an airplane wing generates lift? New
• balloonA helium-filled balloon is tied to the floor of a car that makes a sharp right turn.
• barometerHow would you find out the height of a building using a barometer? New
• bicycle.balanceWhen you ride your bike at constant velocity (say 5 m/s) you tend to keep your balance far easier than when... New
• black.boxA black box with three terminals contains three equal resistors of unknown value, connected either as a delta or as a wye. New
• bomb.testerSome bombs are good and some are duds; a good bomb has a sensor that sets it off if a single photon hits it. New
• brickWhat is the maximum overhang you can create with an infinite supply of bricks?
• bubblesIn a universe with the same physical laws, but which is mostly water with little bubbles in it, do the... Added material
• cannonballA person in a boat drops a cannonball overboard; does the water level change?
• charges.in.sphereEight equally charged particles inside a sphere repel each other and come to rest; what figure do they form? New, unsolved
• charges.on.sphereEight equally charged particles repel each other inside a sphere and come to rest; what figure do they form? New
• coriolisHow large is the Coriolis effect on water flowing down a sink drain, and on an artillery shell? New
• delta.wyeHow can you tell whether sealed black boxes contain three identical resistors connected in Delta or in Wye? New
• doughnutDoes the inner dimension of an iron doughnut increase or [Editor: "of" in the original] decrease when the... New
• duffing.equationWhat exactly is Duffing's equation, and how does the strange attractor associated with it emerge? New
• ehrenfest.paradoxA rigid disk spinning near the speed of light has its rim Lorentz contracted but not its radius; is the... New
• electron.driftHow fast do electrons travel through a wire, and if they are slow, why does the light come on almost the... New
• electrons.on.sphereHow should 8 electrons be placed on a sphere to minimize their energy? New
• fall.into.sunSuppose the Earth suddenly stopped in its orbit. New
• faucetSomeone didn't leave the faucet turned off all the way, so there is a slow but steady leak (i.e. New
• feynman.sprinklerAn S-shaped lawn sprinkler spins one way when water is pumped out of it. New
• floating.cubeIn what position does a floating wooden cube come to rest: flat on a face, on an edge, or with a corner up? New
• fly.and.trainA fly flying towards an oncoming steam train hits its front and is carried along with it. New
• fly.in.bottleA fly is trapped in a bottle which in turn is in a bucket of water. New
• free.fall.throwYou are falling from 1000 feet holding a 30 lb child. New
• gold.and.leadA thief swaps an 18 ounce gold bar for an 18 ounce lead weight on a pressure plate, and the alarm goes off. New
• hair.dryerIf you block the air-inlet for a hair-dryer, the tone of the motor of that hair-dryer seems to rise ... New
• hat.in.riverThe Harvard bridge and the Longfellow bridge are 1 mile apart. New
• heated.ringA metal ring is heated. New
• heavy.electronAn electron is accelerated so close to the speed of light that its (relativistic) mass is 1 kilogram. New
• inclined.treadmillA motorcycle rides on a flat treadmill moving at 40 mph, so that it stays stationary relative to an observer beside it. New
• isotopes.heaviestWhat is the heaviest isotope? New
• juggling.bridgeA woman who weighs 100 lb carries two gold balls, 10 lb each. New
• left.right.aliensExplain which direction is left, and which direction is right, to an English-speaking alien from Alpha... New
• magnetsYou have two bars of iron.
• milk.and.coffeeYou are just served a hot cup of coffee and want it to be as hot as possible later. Added material
• mirrorWhy does a mirror appear to invert the left-right directions, but not up-down? Added material
• monkeyHanging over a pulley there is a rope, with a weight at one end. Added material
• n.switchesWire n switches, a power source and a lamp so that switching any one of the switches changes the state of... New
• pigeonsA 1000-kg truck carrying 500 kg of live pigeons in a sealed cargo compartment pulls up to a weighing... New
• pole.in.barnAccelerate a pole of length l to a constant speed of 90% of the speed of light (.9c).
• primary.colorsWhy are red, yellow and blue the primary colours for paint, but red, green and blue for light, and how does... New
• resistorsWhat is the resistance between various pairs of vertices on a lattice of unit resistors in the shape of a 1. Added material
• return.currentWhy does the return current in the ground plane of a circuit board follow the path directly beneath the... New
• sailA sailor is in a sailboat on a river. Added material
• shoot.sunIf you are standing at the equator at sunrise, where must you point a laser cannon to hit the Sun dead center?
• skidWhat is the fastest way to make a 90 degree turn on a slippery road?
• small.mirrorLooking in a small mirror, do you actually see a larger portion of your face when you hold the mirror farther away? New
• spheresTwo spheres are the same size and weight, but one is hollow.
• spherical.cavityIf all space is filled with rock except a spherical cavity, what is the effect of gravity inside the cavity? New
• spinning.universeI am sitting on a swivel-stool and I push myself so that I start spinning around, and I get dizzy. New
• submerged.balloonA balloon filled with air is completely submerged under water, a weight attached to it. New
• thermal.inversionHow can heat exchange alone (no mixing) bring cold blue water at 1 degree up to 99 degrees using an equal... New
• three.way.switchesHow can three three-way switches (single-pole, double-throw) be wired so that each of them can switch a... New
• time.travel.paradoxIf you went back in time to before you were born to kill your parents, what would happen? New
• train.backwardWhat part of a train is always moving in the opposite direction relative to the rest of the train? New
• train.wheelsThe left and right wheels on a train car are welded to the axle to make one solid wheel-axle-wheel combination. New
• two.boxes.two.lampsHere's a puzzle that requires a slight knowledge of electronics, and some verbal skills: New
• windIs a round-trip by airplane longer or shorter if there is wind blowing?
• yotHow do you get the silver dollar out of the yot, a metal puzzle that looks like a top with a silver dollar... New