Gravity Trivia
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99 free Gravity trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Gravity is the force everyone feels and almost nobody can explain. It keeps the Moon in orbit and the oceans sloshing, it bends starlight, it slows clocks, and for three centuries the best minds in physics have been arguing about what it actually is. These fifty questions run from Galileo's experiments and Newton's law of universal gravitation to Einstein's general relativity and the detectors now listening for ripples in spacetime. Along the way they cover tides, escape speeds, weightlessness in orbit, how hard other worlds pull, and the odd experiments that first weighed the Earth. It suits a physics revision session, a science-themed pub quiz round, or anyone who has wondered why astronauts float and why the Moon never turns its back on us.
30 of 99 questions with answers and explanations. Play the quiz
Q 01How long would a drop through a frictionless tunnel bored right through Earth take to reach the far side?
About 42 minutes
About 42 minutes is the textbook answer for a uniform-density Earth, the same as half the orbital period of a low satellite. A realistic density profile trims the trip to about 38 minutes.
Q 02Gravity on the Moon, where Apollo astronauts bounded along in their suits, is roughly what fraction of Earth's?
About one-sixth
About one-sixth is right: lunar gravity is 1.62 m/s², 16.6% of Earth's. With no air to get in the way, the hammer and feather David Scott dropped on Apollo 15 sank to the dust side by side.
Q 03Crew on the International Space Station, where gravity is still 90% of surface strength, float because they are in what?
Free fall
Free fall is the whole trick: station and crew are falling toward Earth together, but moving sideways at 28,000 km/h so they keep missing it. Calling the condition weightlessness is fine; calling it the absence of gravity is not.
Q 04On most coastlines, how many high tides does the Moon's pull raise in the course of a single day?
Two
Two high tides a day is the norm because the Moon raises one bulge on the side facing it and another on the far side, and Earth turns through both. A few places, such as parts of the Gulf of Mexico, get only one.
Q 05Which Canadian bay, a funnel-shaped basin that resonates with the tide, has the highest tidal range on Earth?
Bay of Fundy
Bay of Fundy tides can rise and fall by as much as 16 metres, against a typical ocean range of about one metre, enough to push the rivers that drain into it backwards twice a day.
Q 06Which planet, with 318 times Earth's mass, has the strongest surface gravity of any planet in the Solar System?
Jupiter
Jupiter's pull at the cloud tops is still less than three times Earth's despite 318 times the mass, because all that bulk is spread through a globe eleven times as wide.
Q 07Ignoring air resistance, how fast must a rocket leave Earth's surface to coast away without ever falling back?
About 11 km/s
About 11 km/s, 11.2 km/s to be exact, is Earth's escape velocity, roughly 40,000 km/h or 33 times the speed of sound. The Moon's is just 2.4 km/s, which is why Apollo could leave it on a single small engine.
Q 08Gravitational waves, ripples in spacetime first directly detected in 2015, cross the universe how fast?
The speed of light
The speed of light is exactly how fast gravitational waves move: GW170817's ripples and its gamma-ray flash arrived within two seconds of each other after more than 100 million years in transit, a dead heat that confirmed it.
Q 09Why does the Moon always show Earth the same face, leaving its far side unseen until a probe flew past in 1959?
Tidal locking
Tidal locking means the Moon spins exactly once per orbit, so the same hemisphere always faces us. Earth's tides braked its rotation into step billions of years ago, and the Moon is slowly doing the same to Earth.
Q 10What nickname did NASA's reduced-gravity aircraft earn from the parabolic arcs that leave passengers briefly weightless?
Vomit Comet
Vomit Comet was the passengers' own name for it, since each flight strings together dozens of plunges and many riders are sick; Project Mercury astronauts trained aboard one in 1959.
Q 11A belly-down skydiver stops speeding up once air drag balances gravity, settling at a terminal speed of roughly what?
About 200 km/h
About 200 km/h, or 55 metres a second, is where drag on a spread-eagled body matches its weight; tucking into a head-first dive cuts the drag and pushes the limit past 300 km/h.
Q 12Because Earth bulges at the equator, which Ecuadorian volcano's summit is the farthest point from the planet's centre?
Chimborazo
Chimborazo's summit is about 2 km farther from Earth's centre than Everest's, even though it stands nearly 2,600 m lower above sea level, which makes it the peak that reaches farthest into space.
Q 13Which Greek philosopher's Physics claimed bodies fall at speeds proportional to their weight, a view Galileo demolished?
Q 21In which German city did Einstein present the final field equations of general relativity to the Academy of Sciences in November 1915?
Berlin
Berlin heard the theory in four weekly lectures that November, and Einstein was still correcting his equations between them: only the last, on the 25th, had them right.
Q 22Tidal friction from the Moon is braking Earth's rotation and lengthening the day by roughly how much per century?
About 2 milliseconds
About 2 milliseconds a century adds up, which is partly why leap seconds exist: they keep atomic time in step with the slowing planet.
Q 23General relativity's first success explained a stubborn leftover drift in Mercury's perihelion of how much per century?
About 43 arcseconds
Aristotle
Aristotle held that a stone ten times heavier falls ten times faster. Galileo noted that tying a small stone to a heavy one should then both slow it and hurry it along.
Q 14Instead of dropping weights from a tower, Galileo mostly studied falling bodies by rolling balls down what?
Inclined planes
Inclined planes slowed the motion enough for Galileo to time it with water clocks, and showed that distance grows with the square of the time. The tower drop, if it happened at all, was over too fast to measure.
Q 15The extra-high spring tides arrive twice a month when the Sun and Moon line up, at which pair of lunar phases?
New and full
New and full moon put Sun, Moon and Earth in a line called syzygy, so the Sun's tidal pull reinforces the Moon's; the name has nothing to do with the season. At the quarter moons the two pulls partly cancel, giving weak neap tides.
Q 16Laser pulses bounced off reflectors left by Apollo crews show the Moon receding from Earth by how much each year?
About 3.8 cm
About 3.8 cm a year is the Moon's retreat, paid for by tidal friction that is also slowing Earth's spin. Run the clock back and the Moon once loomed far larger in the sky, with tides to match.
Q 17If you could stand at the very centre of the Earth, the net pull of gravity on you would be what?
Exactly zero
Exactly zero is the answer: with equal mass pulling from every direction, the forces cancel at the centre. You would still be crushed, not by gravity but by the pressure of everything above.
Q 18Compared with an identical clock on a mountaintop, a clock at sea level, deeper in Earth's gravity well, runs how?
Slightly slower
Slightly slower is right: the closer a clock sits to a mass, the slower it ticks, an effect atomic clocks picked up in 2010 across a height difference of just 33 cm. Your head is ageing faster than your feet.
Q 19How strong is gravity at Saturn's fast-spinning equator, given the planet's 95 Earth masses?
Slightly less than Earth's
Slightly less than Earth's, 8.96 m/s² against our 9.8, because Saturn's mass is spread through a huge, low-density globe and its spin flings the equator outward; at the poles the pull is about a third higher.
Q 20Gravity on Mars, a planet with 11% of Earth's mass, comes to what percentage of Earth's surface gravity?
About 38%
About 38%, 3.72 m/s², is the Martian figure, so a person could jump well over twice as high there as on Earth.
About 43 arcseconds a century, a hundredth of a degree, was the gap Newton's laws could not close, and Einstein's equations matched it with nothing added, ending a half-century hunt for an unseen planet.
Q 24Which hypothetical planet did Urbain Le Verrier propose between Mercury and the Sun to explain Mercury's stray orbit?
Vulcan
Vulcan was hunted by astronomers for half a century; it never existed, and general relativity accounted for the orbit instead. Le Verrier had earned the benefit of the doubt by predicting Neptune the same way.
Q 25Eddington's 1919 eclipse party went to Príncipe; a second team measured starlight bending from Sobral, in which country?
Brazil
Brazil's Sobral team got its sharp plates from a small backup telescope, and they backed Einstein's prediction over Newton's; the main telescope's blurred plates, nearer Newton's figure, were set aside.
Q 26The 2017 neutron-star merger seen in gravitational waves and light forged up to 13 Earth masses of which metal?
Gold
Gold by the planet-load: a single collision may make between 3 and 13 Earth masses of it, so some of the gold in a wedding ring may well be neutron-star shrapnel.
Q 27LIGO's twin L-shaped detectors in Louisiana and Washington measure length changes across mirrors spaced how far apart?
4 kilometres
4 kilometres of vacuum pipe in each arm lets LIGO sense a stretch of less than a ten-thousandth of a proton's width, among the tiniest measurements ever made.
Q 28Virgo, Europe's gravitational-wave detector and LIGO's partner, sits outside which Italian city, Galileo's birthplace?
Pisa
Pisa is a short drive from Virgo's site at Cascina, and the detector's data helped narrow the 2017 neutron-star merger to a patch of sky small enough for telescopes to find its galaxy.
Q 29What is the nickname of the first confirmed gravitational lens, a distant object found in 1979 to appear more than once?
The Twin Quasar
The Twin Quasar is one object split in two by the gravity of a galaxy in front of it, and light along one path arrives about 14 months after the other.
Q 30The Bullet Cluster, where lensing maps show mass sitting apart from the hot gas, is prized as evidence for what?
Dark matter
Dark matter is the simplest reading: when two galaxy clusters collided, the lensing mass sailed on with the galaxies while the hot gas, most of the ordinary matter, lagged behind.