50 Fun Facts About Physical Science

Stars are almost pure balls of which state of matter, estimated to be 99.9% of all ordinary matter in the universe?

Plasma is a gas so hot its atoms have been stripped of electrons, which is why it conducts electricity and glows in neon signs and lightning bolts.

When Apollo 15's David Scott dropped a hammer and a falcon feather side by side on the Moon, what happened?

They landed together because the Moon has almost no atmosphere, so no drag slowed the feather, exactly as Galileo had predicted centuries earlier.

Lakes freeze from the top down because liquid water is at its densest at roughly what temperature?

4 °C is where water is heaviest, so the colder water near freezing floats on top and ice forms there first, leaving fish alive underneath all winter.

An 80 kg astronaut keeps the same mass on the Moon, but their weight there drops to roughly what fraction of Earth's?

One sixth is the figure because gravity on the Moon is only about 1.6 m/s², so a suited astronaut could bound along despite carrying 80 kg of kit.

Ice is roughly 10 percent less dense than seawater, so how much of a floating iceberg sits below the waterline?

About 90% of an iceberg is hidden underwater, which is why the Titanic's lookouts saw only a small peak and why 'tip of the iceberg' means what it does.

Sound moves at 343 m/s in air; through fresh water at 20 °C it travels roughly how much faster?

About four times as fast, at 1,481 m/s, which is why whales can call across whole ocean basins and why sonar works so well underwater.

Mixing red, green and blue light at full strength, as the pixels of a TV screen do, produces which colour?

White is what all three light primaries add up to, the opposite of paint, where mixing every colour in the box gives a muddy dark brown.

Gravity at the International Space Station is still nine-tenths of its strength on the ground, so why do the crew float?

They are in constant free fall, along with the station itself, which is moving sideways so fast that it keeps missing the Earth as it drops toward it.

Dry ice used for stage fog leaves no puddle because solid carbon dioxide turns straight into gas, a change called what?

Sublimation skips the liquid stage entirely: under ordinary conditions carbon dioxide has no liquid form, so the solid simply vanishes into gas at −78.5 °C.

Which particle's count in the nucleus, the same for all an element's isotopes and ions, fixes its atomic number?

Protons carry the nucleus's positive charge, and every atom with six of them is carbon, however many neutrons it has packed in alongside.

Helium, neon and argon, which almost never form compounds, make up which group on the far right of the periodic table?

Noble gases were long called the inert gases because their full outer electron shells leave them nothing to gain from bonding; the first compound of one was only made in 1962.

Lithium, sodium and potassium, which fizz or even burst into flame when dropped in water, form which group of elements?

Alkali metals get more violent the further down the group you go: potassium reacts violently at room temperature, and caesium explodes even in cold water.

Silicon and germanium, the elements behind computer chips, sit on the periodic table's zigzag line as which class?

Metalloids are only fair conductors of electricity, which is exactly what makes silicon useful: its conductivity can be tuned, the basis of every transistor.

Which chemists' counting unit is celebrated every 23 October from 6:02 am, a nod to the 6.02 × 10²³ particles it holds?

Mole Day's 6:02 on 10/23 spells out Avogadro's number, and one mole of any substance is the same headcount of particles, from water to uranium.

On the pH scale, usually given as running from 0 to 14, pure water at 25 °C sits at which value?

7 is neutral only at 25 °C: warm the water and its neutral point slips below 7, while staying neutral, because more molecules split into ions.

Instant cold packs for sports injuries chill because dissolving ammonium nitrate in water is which kind of process?

Endothermic processes pull heat in from their surroundings, so the pack drops to near freezing moments after the inner water bag is burst.

Platinum in a car's exhaust converter plays which role, speeding up reactions while coming through them unchanged?

Catalysts are not consumed by the reactions they speed up, which is why a few grams of platinum and rhodium can clean a car's exhaust for its whole working life.

Galvanised steel, whose coating corrodes in place of the iron beneath it, owes its rust resistance to which metal?

Zinc acts as a sacrificial layer, corroding first so that even a scratched coating keeps protecting the steel, which is why galvanised buckets and railings last for decades.

In table salt, each sodium atom hands one electron to a chlorine atom, forming which type of chemical bond?

Ionic bonds are the pull between the charged ions left behind, which lock into a rigid lattice, so salt forms hard, brittle crystals that shatter rather than bend.

Which property, described by Newton's first law, makes standing bus passengers lurch forward when the bus brakes?

Inertia means the passengers simply keep moving at the bus's old speed while the bus itself slows beneath them, which is also why seat belts exist.

Which of Isaac Newton's laws explains how a rocket accelerates in empty space, where there is nothing to push against?

The third law says every action has an equal and opposite reaction: the rocket throws hot gas backwards, and the gas pushes the rocket forwards just as hard.

A skydiver stops speeding up once air resistance balances their weight; what is this steady top speed called?

Terminal velocity is reached when drag exactly cancels weight, so a skydiver falls at a steady rate until the parachute opens and a far slower balance is struck.

Under the inverse-square law, tripling the gap between two masses cuts their gravitational pull to what fraction?

One ninth, because three squared is nine: gravity thins out over an ever-larger sphere as the distance grows, so it fades fast but never quite reaches zero.

Big Ben's pendulum is 4 m long to give a two-second beat, because a pendulum's period is set chiefly by what?

Its length is all that matters for small swings, and the bob's mass makes no difference, so a clock is sped up by shortening the pendulum and slowed by lengthening it.

A sharp knife cuts better than a blunt one because the same push on a smaller edge gives more of what?

Pressure rises as the same force is squeezed onto a smaller patch, which is also why a thumbtack's point sinks into a wall while its flat head does nothing.

A loading ramp is the simplest form of which classical simple machine, of which a screw is a wrapped-around version?

Inclined planes trade distance for force: moving a load up a long gentle slope takes less effort than lifting it straight up, which is why mountain roads switchback.

Which tool is a second-class lever, with the load between the pivot and the effort, just like a wheelbarrow?

Nutcrackers, like bottle openers and wheelbarrows, always multiply force, because the load sits closer to the pivot than your hands do.

By which method of heat transfer does the Sun's energy cross 150 million km of empty space to reach Earth?

Radiation needs no medium at all, which is why the Sun's warmth arrives across a vacuum where conduction and convection are both impossible.

Which spring law is named for the 17th-century English scientist who also coined the biological word 'cell'?

Hooke's law says a spring's stretch is proportional to the force on it, a discovery Robert Hooke first announced as a scrambled Latin anagram to stake his claim.

Which part of the electromagnetic spectrum has the longest wavelengths, from a rice grain's width of a millimetre up?

Radio waves also carry the lowest frequencies in the spectrum, below 300 gigahertz, and AM, FM and Wi-Fi all live somewhere in that enormous band.

Sound travels through air as which type of wave, with the air squeezed and stretched along the direction of travel?

Longitudinal is the Slinky kind: push one end and the bunched-up coils travel along it, exactly as bunched-up air travels across a room to your ear.

Turning up a speaker's volume increases which property of the sound wave, while leaving its pitch unchanged?

Amplitude is the size of the wave's swings: bigger swings mean more energy and a louder sound, while pitch depends on how many swings pass each second.

Sound above roughly what frequency counts as ultrasound, the range bats and porpoises use to find their prey?

20,000 Hz is roughly the upper limit of hearing for healthy young adults, and Lazzaro Spallanzani showed in 1794 that bats hunt by inaudible sound rather than sight.

Which colour of visible light has the shortest wavelength, at about 400 nanometres?

Violet light has the highest frequency our eyes can register; just beyond it lies ultraviolet, which we cannot see but which still burns skin.

A pencil in a glass of water looks bent because light changes speed as it leaves the water, an effect called what?

Refraction is also what lenses, including the ones in your eyes, rely on, and it splits sunlight into a rainbow when raindrops bend each colour by a different amount.

Short-sightedness, where distant objects blur, is corrected with spectacles that use which shape of lens?

Concave lenses spread light out before it enters the eye, pushing the focus back onto the retina, a fix Johannes Kepler worked out in 1604.

Counting from a lightning flash to its thunder, roughly how long does sound take to cover each kilometre?

About 3 seconds per kilometre, so a five-count gap means the strike was well under two kilometres away, and a flash with an instant crack means it was very close.

In which type of circuit do the other lights in a house stay on when one bulb burns out?

Parallel wiring gives every bulb its own loop back to the supply, whereas in a series circuit one dead bulb breaks the path for all of them.

On the decibel scale, a rise of 10 dB means a sound's power has been multiplied by how much?

10 times more power for every 10 dB, so a 30 dB jump is not three times the power but a thousand times, which is why the scale is logarithmic.

Scrapyard cranes lift and drop scrap steel using which device, a coil of wire that is magnetic only while current flows?

Electromagnets lose their field the instant the current stops, which is what lets a crane drop its load, and the same trick works inside doorbells, loudspeakers and MRI scanners.

A bicycle dynamo that lights a lamp from the turning wheel is a small version of which power-station machine?

Generators turn motion into electricity, and a motor is the same machine run backwards: spin a motor's shaft by hand and it will produce a current.

Power stations step electricity up to hundreds of thousands of volts before it travels along pylons to reduce what?

Energy loss in the cables falls because a higher voltage means a smaller current for the same power, and it is current that heats the wires.

Heating an iron magnet above about 770 °C, its Curie temperature, does what to it?

It loses its magnetism because the heat jostles its atoms out of alignment, a threshold that Pierre Curie showed every magnetic material has.

Which gas, about a fifth of the air, makes a glowing wooden splint burst back into flame in the classic school test?

Oxygen makes the ember flare because burning is a reaction with it, and the more concentrated the gas, the faster the splint burns and the fiercer the flame.

Flour dust in a mill can explode while bagged flour only smoulders, because grinding a solid hugely increases its what?

Surface area is what a reaction feeds on, and a dust cloud exposes so much of it that a Minneapolis flour mill blew up in 1878, killing 18 people.

Which French chemist, guillotined in 1794, showed that a chemical reaction leaves the total mass of matter unchanged?

Antoine Lavoisier weighed everything going into and out of sealed reactions, and the conservation of mass he confirmed is why chemical equations must balance.

We only ever see one face of the Moon because its spin and orbit take the same time, a state called what?

Tidal locking is the end state of billions of years of Earth's gravity braking the Moon's spin, and Pluto and its moon Charon have done it to each other.

A total solar eclipse can happen only at which phase of the Moon, when it passes directly between Earth and the Sun?

New is the only phase with the Moon between us and the Sun, and even then its tilted orbit usually carries its shadow above or below Earth, so totality is rare.

Tungsten bars have been plated to pass as which precious metal, whose 19.3 g/cm³ density tungsten almost matches?

Gold and tungsten differ in density by less than half a percent, so a plated tungsten bar weighs exactly what a real bar of the same size should.

To coast away from Earth for good on launch speed alone, ignoring air drag, a projectile needs roughly what speed?

11 km/s, some 40,000 km/h, is Earth's escape speed; real rockets never hit it in one go, accelerating steadily instead so the air does not tear them apart.