When you flush the toilet in Australia, does the water swirl the other way?

When you flush the toilet in Australia, does the water swirl the other way?

coriolis effect


The flushing of toilets

coriolis effect

You’ve probably heard about the Coriolis effect many times. And maybe you’ve even, like me, watched in awe, on your first day in Australia, after being to the toilet… Staring down the drain to see if it’s any different. Well, I’ve never seen it… The difference that is. It’s a toilet, it swirls and it flows. Same with the sink… It swirls and it goes out the hole in the bottom. Maybe I haven’t really been paying attention. But I haven’t noticed anything extraordinary.

The Coriolis effect

There is in fact a physical and measurable reason why the water in the northern hemisphere swirls anti-clockwise and the water in the south swirls clockwise. And the reason is called the Coriolis effect. This is how it works:

If you stand on a merry-go-round in motion and throw a ball towards the center. Because you’re not still but moving, the ball subjectively will not travel in a straight line but turn. This is the case also if you throw the ball outwards. 

The Coriolis effect and huge things like the Earth.

The mystical, swirling force isn’t really a force at all. It doesn’t do anything with the agent, it just looks that way. The subjective doing is caused by the earth’s rotation. 

coriolis effect

Now imagine you stand on the Equator and throw your ball towards the north pole. The Earth moves to the right, from west to east. Now, since you, at the Equator, have a higher vertical speed than the north pole, the ball will conserve that higher vertical speed and travel towards the east. The subjective eastward, vertical speed will be higher the closer to the pole it gets. Because of the Coriolis effect, it will turn right, towards the east.

coriolis effect

If you stand on the north pole and throw the ball towards the equator, the ball will subjectively travel west. This is because at the north pole it has no vertical speed whatsoever. But the further south it travels, the more speed the earth has. For every mile the ball travels, the earth travels toward the east, and it will seem, because of the Coriolis effect, as if the ball turns right, towards the west. 

Weather, winds, and currents.

So going north the ball travels east, subjectively towards the right. Going south the ball travels west, subjectively towards the right. And this gives an anti-clockwise vortex to things moving inwards in the northern hemisphere. And consequently, a clockwise motion to things moving inwards in the southern hemisphere. Inwards meaning low-pressure weather systems e.g. 

High-pressure systems obviously swirl the other way. In the northern hemisphere, they turn clockwise, because the pressure pushes the air outwards. And in the south they go anti-clockwise.

This Coriolis effect has an important role to play when it comes to winds, ocean currents, hurricanes, etc. For example, the trade winds have brought sail ships over the oceans for centuries. The persistence and stability of these winds are caused by this force.

The Coriolis effect and small things like toilets and sinks.

But let’s get back to our toilet. A sink, a bowl, or a toilet is small. It’s very small compared to a weather system or a trade wind. It’s so small, in fact, that the Coriolis effect has no measurable effect whatsoever.

It’s a strong myth, and it is hard to debunk. Many sustain that even if the effect is small, it would be possible to show it in a controlled environment… Like a laboratory for example. Until today, that hasn’t happened. Nobody has ever shown that the Coriolis effect could have any impact on water draining from a small container. (Please take me up on that one. I’d love to be wrong here…)

To better understand how small the Coriolis effect really is, imagine you’re standing on the north pole. You wash your hands and then you pull the plug at the bottom of the sink. Could the circular movement of the ground on which you stand, one complete turn in 24 hours, make the water move? 


The Coriolis effect is very real and has an enormous impact on our daily life in the form of weather, winds, airplane routes, currents, and more. But it couldn’t move such a small quantity of water. The swirling depends on many other things, like the form of the container, the initial instability of the water volume, the position of the drainage, even the difference in temperature in the water, from left to right, from the surface to bottom. 

The Coriolis effect has no measurable effect on such a small quantity of water.

the north pole
courtesy of Eli Duke

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No, the swirling in such small basins is random. You need big things like weather systems for the Coriolis effect to be noticable.



Can you break a glass just by singing for it?

Can you break a glass just by singing for it?

break glass by singing

Breaking glass with voice. 

The human voice is a strange and unique instrument. No other species has the capability to vary the sound as much as a human being. That’s, of course, because we communicate with words. And to pronounce words we need a lot of variations to the sound of the voice… The vowels. There are five vowels in English, but 20 vowel sounds. In other languages there can be many more, And then there are all the consonants. The jaw moves up and down, and the tongue in all directions.

Breaking glass with voice

Maybe that’s one of the reasons, human beings like to sing. We are actually very good at it, at least some of us are.

The thing about the voice is that it can’t produce very strong sounds. The Opera-singer doesn’t really sing in a loud voice. It’s more of a very focused voice, one that has a metallic ring to it. That ring passes through the sound of the orchestra. Then the audience’s brains put an imaginative voice to the high-pitch ringing sound that they hear. And suddenly the small vocal cords of 1,5 centimeters sound all the way to the back of the concert hall. It’s magic.

The frequency

Every sound has a frequency. That’s what the black and white keys on the piano are for. When there’s a sound, all the information of that sound travels through the air as sound waves. When a sound wave hits the eardrum, the latter vibrates with the soundwave. All the information about the sound is then transmitted to the brain. And we can tell if the voice was good, bad, soft, powerful, and we understand the frequency. We know if it’s in tune.

And every object has its own frequency. If you knock on it, it will put out some sort of sound, a tune. The frequency depends on the material and the shape. That’s why a Stradivarius Violin costs several million dollars and a new handmade Chinese Violin can cost a few hundred, although they’re both handmade out of wood. The Violin’s own frequency, the resonance is different.

Breaking glass with voiceThe breaking theory

If you want to start breaking glass with your voice, here’s how you do it. When an elastic body vibrates, it vibrates at the body’s natural frequency. These vibrations are called Natural Vibrations. Forced Vibrations are vibrations coming from an external source, a voice or a loudspeaker for example. If the Forced Vibration is the same as the Natural Frequency, the vibrations’ amplitude increases manifold. If the increase of the vibration from the external force is more than the decrease from the resistance in the material, the vibration builds up. 

To start breaking glass with your voice, you need to find the glass’ natural frequency. Then you have to put more sound energy into the glass than the glass is able to dampen. In that case, the vibrations will build-up, and if you continue, eventually it will break. 

Break glass by singing – This is what you need

  • You need a glass. Choose one with a big cup and thin walls. It should have a good ring, natural frequency, to it.  Knock on it or move your wet finger on the rim, to hear the sound. The vibration mustn’t die out fast but continue for a while.
  • Then you need to prepare the surroundings, protect your mouth, eyes, and body, and get children and dogs out of the way. You’re breaking glass here… (Actually, you should keep your mouth as close as possible, and doing so is risky. You shouldn’t do it alone. And use some sort of protection for your eyes.)
  • Put it on a table at the height of your mouth. Or hold it in your hand. The glass has to be empty.
  • Find the frequency and sing that note. When you sing the right note and stop suddenly, the glass should continue for a few seconds. If it doesn’t, it’s not the right frequency. You could try different vowels.
  • When you got the frequency right, you just have to produce a loud sound. You would need a very strong voice to break the glass by singing… At least 100 -105 dB. And you need to keep the exact frequency for a long time, to make it build up.
  • If the glass has some small defect, a very small undetectable crack, it’s much easier. A perfect glass is close to impossible to break. Try another one if you don’t succeed.
Enrico Caruso

Now, to who actually can do it

It is said that the famous tenor Enrico Caruso was able to break a glass with his voice. His wife claimed he never did it though.

Many other Opera singers have had that epithet too, like the Swedish soprano Birgit Nilsson, the famous Maria Callas, and others. Even Ella Fitzgerald remembered in an interview how she in 1972 at an audition for Memorex, cracked a glass by singing How high the moon by Morgan Lewis.

And in the end, if you just want to get the glass broken, it’s not difficult at all. I do it all the time…

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Yes, you can brake a glass just by singing. But it’s not only the strength of the voice that does it. It depends on the glass, and on the pitch.



Is the Great Wall of China the only man-made building detectable with the naked eye from the moon?

Is the Great Wall of China the only man-made building detectable with the naked eye from the moon?

Great Wall of China from space

The Great Wall of China from space.

The Wall that separated imperial China from the barbarians of the north, is not one, but many. And it wasn’t built in one moment but in the arc of thousands of years. 

The beginning of the Wall-building started as far back as in the Spring and Autumn period (770–476 BC). At that time China wasn’t united but various Chinese KIngdoms fought one another for the sovereignty. The simple walls from stone or stamping earth were more to divide the different dynasties from east to west than to defend from attacks outside the Chinese territory. 

When Qin Shi Huang unified China in 206 BC, he started to tear down the parts of the wall within his united Empire. And he reinforced and connected the parts facing north. 

The danger to the newborn Chinese Empire was coming from the steppe in the form of invasions or raids from the one or more of the nomadic tribes.

Great Wall of China from space
Courtesy of Keith Roper

Later, the following Dynasties all repaired, rebuilt, and expanded sections of the Great Wall. As the borders of China changed during the centuries, the stretch of the wall changed. Some Dynasties who were closer to today’s Mongolia built walls. The Khitan- and Jurchen (Manchu-) Dynasties built walls as far north as inside Russia. These parts do not connect to the Great Wall we see today. 

There’s even a wall to the south, close to the ancient town of Huangsiqiao,

The Ming Dynasty

In 1279, the Mongols and Kublai Kahn conquered all of Chine and brought it under control of the Yuan Dynasty. When the Mongols were defeated in 1368, Zhu Yuanzhang, the first Emperor of the Ming Dynasty came to power. He and all the Emperors after him reinforced and enlarged the Wall. They felt the need to defend China against the Mongols, against whom they had failed to get a definitive military upper hand. The parts of the Wall that are from the Ming Dynasty, are stronger, and better defended. These are the best-preserved parts. And these are where tourists come in thousands every day to visit and take pictures. 

The Ming Dynasty Wall alone is 8850 kilometers (5500 miles). And it is not only a wall, but transportation routes, barracks, fortifications, toll stations as well. It is a huge defense construction.

great wall of china from space
Courtesy of Maximilian Dörrbecker (Chumwa) / CC BY-SA

The numbers

The Great Wall of China from space, or from walking on top of it, is this big:

  • The total length is 21.196 kilometers (13.170 miles). The Ming Dynasty-part (The widest, highest, most intact, and best-preserved part of the Wall) is 8,850 kilometers (5,500 miles) long.
  • The average height is 6 to 7 meters (20 to 23 feet). The tallest parts are 14 meters (46 feet). The lowest part is only 1 meter (3,3 feet)
  • The average width is 4 to 5 meters (13 to 16 feet). The widest part is 16.7m (54.8ft) and the narrowest is only 70 centimeters (2,3 feet). That’s the same part of the Juyongguan Great Wall that has a height of 1 meter. The width is greater at the base.

The human eye

great wall of china from space

The human eye is a wonderful tool. It can function in bright sunlight, and it can see in almost complete darkness. It can focus on a tiny insect, or it can watch the stars, It can determine distance, and it can see all the colors of the rainbow. But can it see the Great Wall of China from space?

A human eye has a maximum angular resolution of approximately 280 microradians. From 10.000 meters a pixel would be big as a bus. But there’s more to it than just the eye. The brain can compensate for the lack of pixels by moving the eye slightly. Then we have two eyes, and both of them face the same direction. Together they can determine distance, although that only works up close. But they can compensate for each other and increase the details further on objects far away.

fold a paper
Courtesy of Ana Sofia Guerreirinho

So, maybe you can see not only a bus from 10.000 meters but even a small car. But that would probably be the smallest detectable object, and you would have to have 20/20 vision. 

Great Wall of China from space and beyond

So, can you see the Chinese Wall from the moon? A very unscientific way to test it could be to go out at night and look at the full moon. If there was a Great Wall of China up there, would you be able to see it? No, it would be impossible. Most people would agree to that.

How small objects can you see on the Earth’s surface from the moon? The theoretical calculation gives a minimum size of about 800 kilometers (500 miles) width. Adjusted for the brain’s excellent way of handling the multiple information from the two eyes, gives a minimum size of about 350 kilometers (200 miles) in two directions. Given the viewing angle, the atmosphere with clouds, and the fact that most people don’t have 20/20 vision, it could very well be difficult to detect Florida. Let alone a stone wall that is less than 10 meters (30 feet) wide.

Earth from Space
The Hubble Space Telescope. Altitude 60 km (37 miles)

Great Wall of China from space

Let’s get a bit closer. The International Space Station has a target altitude of 40 km (25 miles). At that level, a theoretical minimum detectable object of over 100 meters, could possibly become 50 with the arguments mentioned above. But that’s still more than 5 times the width of the Great Wall of China from space. 

Another unscientific experiment you could try is to look at the Wall with Google Earth. There you notice that at a height of around 25 kilometers you lose it. In fact, astronauts from the ISS claim that you can’t see it with the naked eye. It’s simply too far away, and it’s too small.

From the ISS you can see the Palm islands of Dubai, the Pyramids, the Kennecott Copper Mine in the US,  the Greenhouses at Almería in Spain, some very big roads, and bridges, and dams… And a whole lot of other stuff.

From the moon… Well, it’s just too far away to see anything man-made. Man is just too insignificant.

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No, you can’t see the Great Wall of China from the moon. You can’t see it even from the International Space Station. You could probably detect it from an airplane at 10.000 meters (33.000 feet), on a clear day.



Could a normal, healthy, grown man have outrun a Tyrannosaurus Rex?

Could a normal, healthy, grown man have outrun a Tyrannosaurus Rex?

T-rex run

The Tyrannosaurus Rex… King of kings.

Tyrannosaurus Rex was one of the biggest carnivorous dinosaurs that ever walked on planet earth. Recent discoveries show that it could have reached more than 40 feet (12 meters) in length and weighed almost 10 metric tons. It had enormous, centrally placed back legs but the front legs were very small. Scientists still argue if they were of any use at all. The most probable explanation would be this:  As the head, with time, grew bigger and stronger, much of the muscles holding and moving the heavy skull and working the powerful jaws interfered with the upper arm- and shoulder musculature. Natural selection promoted the head over the arms. Much like modern times birds. It was a bite, pull, shake and twist kind of movement. And for that, no arms were needed.

The head was 5 feet (1,5 meters) long with a monstrous mouth full of razor-sharp teeth, which could reach 6 inches (15cm) in length. New computer models show that it had a rigid skull, much like modern days Alligators. This would increase the estimated power of the jaws, and the bite force could have been as much as 60.000 Newton. That’s about four times the saltwater crocodile chomping record of about 16.000 Newton. A T-Rex would have had no problem eating the cars in Jurassic Park. It had the most powerful bite force of any land-living animal ever.    

tyrannosaurus rexWhere, and when did it live?

The T-Rex lived in North America, which at the time was cut off from South America and much closer to Europe. It preferably inhabited semi-tropical, open forests or coastal habitats. It fed on big dinosaurs and carcasses. A lot of discussions are going on about if it ate live prey or if it was more of a scavenger. The size and the T-rex’s relatively slow running speed have questioned if it could hunt at all. Nowadays consensus is that it probably did both. Just like any of today’s big predators, it wouldn’t refuse a meal if it was already served.  

It lived during the late Cretaceous period, 85 million to 65 million years ago.

It was extinct 65 million years ago when a huge asteroid hit Mexico, the so-called  Cretaceous–Paleogene (K-Pg) extinction event. In a very short period, three-quarters of all living species on earth died. All land-living dinosaurs, with the exception of avian species, perished.

But I’ve seen it chase a jeep in the film Jurassic Park…

The truth is that we can’t know everything about the dinosaurs. It’s a guessing game based on fossils and chemical analysis. It is difficult to determine the color for example. We have to try and find substances on and around the fossils and go from there. Lately, it’s been discovered that the gigantic beasts probably had feathers. Not like birds, but still some sort of hairy covering on top of the trunk. 

The jeep scene in Jurassic Park is regarded by most scientists today as non-realistic. There’s just no way a T-rex could run that fast. And it probably wouldn’t even try to chase the jeep. The hunting technique wasn’t up for it. It was more of a big elephant than a lion. 

t-rex runSo, how fast can a T-rex run?

Recent studies consider not only muscle mass, weight, and size, but also bone resistance for example. The huge muscles would also require anaerobic combustion during acceleration. As it couldn’t keep that up for very long, the time available for reaching top speed was limited. It would also have to use a considerable amount of energy to move all that weight. Put into computer models, all this new data gives that the T-rex could run 15 mph (24 km/h) at most. Steady jogging rather than sprinting. 

In fact, among all reptiles, mammals, and sea animals the fastest animals are of small to medium size. 

And how fast can an average man run?

The world record for 100 meters is 9,58 set by Usain Bolt in 2009. Calculating the time for acceleration, reaction to the start signal, and slowdown at the end of the track, the top speed during his world record race is 27 mph ( 43,5 km/h). That’s phenomenal. And not everybody can run like that… Nobody can, not anymore. 

An average, fit man in his 30s or 40s could do it in 15 seconds. Doing the exact same calculations we end up with a top speed of around 16 mph (26 km/h).

That is actually faster than the T-rex. But, it’s the absolute top speed. He probably wouldn’t be able to keep that up for more than a few seconds. After that, the Dinosaur will gain on him. And the 15 seconds is on an absolutely flat track, In terrain, he would be much slower. 

Man running
Courtesy of the Maryland National Guard

The average man could be faster than this or he could be slower. The T-rex could be old and tired or young and strong. Any way you look at it, it would be a very close shot. 

Putting emphasis on the word COULD, then it is possible. Usain Bolt definitely could outrun a T-rex, but any ordinary man could too, even if it would be close. 

But if the T-rex run was so slow, how did it catch its prey?

The T-rex runs slowly, and it probably was something of an opportunist, eating what it could find, attacking young or sick animals… Or already dead ones. Its ferociousness and gigantic size put it at the top of the nutrition chain. And there it could eat about anything, as long as it wasn’t too fast or too small.

This is something we can see today as well. The biggest creatures in the sea, the whales, eat plankton. It’s a question of economy. They just wouldn’t be able to eat enough to compensate for the energy they would lose hunting.  Not if they went after big, fast, and strong prey. Either you eat a lot, or you consume very little preparing your meal.  

The T-rex wasn’t able to run very fast. Maybe it was the maximum possible size of a carnivorous animal on earth. Bigger than that, and you have to eat something that is sitting still… Like grass.

What else should you do if you were unfortunate enough to encounter one?

The other idea of Jurassic Park, that you should stand still, is also wrong. The T-rex had huge eyes facing partially forward. It could probably spot a man from miles away… And it could probably determine the distance at least as well as we can. It would have no problem finding you even if you stood absolutely immobile. 

Running away would still be your best option. If you could find dense vegetation somewhere, that would be the place to go. 

The T-rex would run with 10 tons of weight on its shoulders.

It wouldn’t be agile. So you could try the old Rhinoceros trick. Stay put, until he’s a few meters away. Then run at a 90° angle to the right or to the left. The Tyrannosaurus would probably continue straight ahead for a bit before he could turn. You would need nerves of steel for that though….

Maybe it’s still better to head for the bush…

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Yes, a normal, healthy, fit man could have outrun a Tyrannosaurus Rex, even if it would have been a very close shave. 

t-rex run



If you fold a paper 42 times, will it reach the moon?

If you fold a paper 42 times, will it reach the moon?

fold a paper

The thing about doubling

Fold paper 42 times – The art of doubling.

We have a limited brain. At least most of us have. We are often more prone to use common sense than to operate mathematical theorems. Even if maths sometimes is as obvious as everyday street smartness. 

fold a paper
Courtesy of Ana Sofia Guerreirinho

The old folded paper problem isn’t all that strange if you look at it. It’s all about doubling, and doubling builds up fast. In the beginning, it’s slow but once you reach important figures, the doubling becomes impressive. Double 2 and you get 4, but double 100.000.000… Yes, you see the trick here.

The mathematical explanation

The mathematical explanation looks like this

h=o x 2^(n) where h is the height of the folded paper, o is the thickness, and n is the total number of folds.

If the first fold gives you 0,2 mm, the second will give you 0,4, and the third 0,8. Already at 8 folds, you’re at an inch, 25,60 mm. And 8 is about the maximum folds you can accomplish. Disclaimer: No, you can’t fold a paper 42 times. This is all a theoretical experiment. Mythbusters folded a paper 11 times with the help of a forklift, but that’s an exceptional deed. 

At 11 folds you have 204.80 mm, almost a foot. At 15 folds, 3.276.80mm. At 20, 104.857.60 and now we have to start counting in kilometers. At 25 we reach 3,35 kilometers, more than 2 miles and we’re heading out of the atmosphere. At 30 folds, we’re 107 km (67 miles), At 35 folds, almost 3500 km ( more than 2000 miles). Closing in on the moon, at 40 folds we are about 110.000 km (68.000 miles) out in space, and two more folds we arrive at the final number… The total of 439.804.651.110 mm 439.804.65 km (273.281 miles and 653,39 yards). The average distance to the moon is 384 400 km

fold a paper
spread-sheet Height of a folded paper

Another famous story 

The magic of doubling has been used many times. By mathematicians, but also as entertaining stories. 

The board game, Chess, was invented in northwest India sometime around the 3rd or 4th century. From there it spread to China and when it was introduced to the Emperor, he wanted to honor the merchant who brought this wonderful game to the knowledge of the son of Heaven. And he wanted to reward him with a gift.

 –   What do you want, he asked.

 –   Son of Heaven, said the merchant lying on his belly with his face to the ground. I am a poor man, and all I want is some rice.

 –   So be it. But how much do you want? asked the Emperor.

   I want only one single grain on the first square of the chess board, and two on the second, four on the third, and so on until the last square. 

 –   Your wish shall come true, said the Emperor, who wasn’t very knowledgeable in science and mathematics. 

Courtesy of Andrea Schiavon

The fact is that what he had agreed to give to the merchant was 18.446.744.073.709.551.615 grains of rice, with a weight of 1199.000.000.000 metric tons. That’s 1700 times the world production of rice today and probably more than the total of all rice that has ever been produced in all the world since the beginning of time. The Emperor wasn’t happy.

The second half of the chessboard.

“The second half of the chessboard” is a phrase and concept, introduced by Ray Kurzweil. The idea is to look ahead and understand the power of exponentiality. If the first half of the chessboard is very big, then the second half is so much bigger, that it can be difficult to even grasp. The first square of the second half is already bigger than the total of the first 32 squares. And the total of the second half is times bigger than the total of the first half. 

This idea has a significant impact on the business strategy of a company or an organization.  

In the end, it’s also important to remember that, just as it would be impossible to fold a paper 42 times, the exponential growth only works within a certain interval. The merchant in China didn’t get all he was owed. But instead, he got his head chopped off.

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Yes, if you could fold a paper that is 0,1 mm thick 42 times, it would reach the moon and more. 



Did Newton get the idea of the law of gravity, when, sitting under a tree, he was hit on the head by a falling apple?

Did Newton get the idea of the law of gravity, when, sitting under a tree, he was hit on the head by a falling apple?

newton's law of gravity

Isaac Newton’s apple story

Sir Isaac Newton was born in Lincolnshire in east England on January 4, 1643. He was a mathematician, a physicist, an astronomer, and a theologian. He was one of the most famous researchers of his time and is regarded as one of the most influential scientists of all time.

In 1687 he came out with his book Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). In it, he used mathematic formulas to explain the motions of objects in space. He showed how to apply the same mathematical principles on various bodies on earth, he calculated trajectories of comets, the rise, and fall of the tide, and he formulated the Law of Gravity. He laid the foundation of Classical Mechanics.  

Newton’s law of gravity

Newton’s law of gravity explained the force of attraction between two objects. He did not, however, discover gravity. The fact that bodies attract each other had been discussed among scientists before Newton. What Newton did was demonstrate the exactness of the inverse-square law of attraction through mathematical calculations. 

This is how it works:

Newton's law of gravity

Every point mass attracts every single other point mass by a force acting along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between them.

Newton’s apple story

The Newton’s-apple story originates from when he was already a well-established scientist, and it exists in many versions. The occasion should have been when Newton, due to an outbreak of the Bubonic plague in 1666, had to leave Cambridge (where he was studying at Trinity College) and return to his mother’s house in Lincolnshire. 

It’s obvious that Newton liked the story and told it often to entertain and amuse his friends. The fact that it contains a falling fruit that is round, explains very well the idea of attraction between bodies. The earth attracts the apple and the apple attracts the earth.

newton's law of gravity

The Apple is also a mythical and religious symbol. As Newton had a very intimate relationship with the Holy Bible, he would use an object that refers to originality and maybe even wisdom… The forbidden fruit in Eden. 

What we know is that Isaac Newton told the story to his friends, but we have no idea if it is true.

And Newton’s apple story never actually included an apple bonking him on the dome. He mostly told that he saw it falling. As in the book “Memoirs of Sir Isaac Newton” by William Stukeley… 

After dinner, the weather being warm, we went into the garden, & drank tea under the shade of some apple trees… he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. Why should that apple always descend perpendicularly to the ground, thought he to himself; occasioned by the fall of an apple, as he sat in a contemplative mood

Newton’s law of gravity, was it really such a revolutionary discovery?

As mentioned before, it was probably not a Eureka experience. It was not like Isaac Newton is sitting under the tree and suddenly he understands that we don’t fall off the earth because there was such a thing as gravity. He was a scientist and he did scientific calculations about things around him. 

newton's law of gravity

When Newton’s book, Philosophiæ Naturalis Principia Mathematica (or “the Principia” in short), was published on July 5, 1687, Robert Hook, a fellow English scientist and member of the council at Royal Society, claimed that it was he who had given Newton the idea of the inverse-square law. But this is highly unlikely.

Surely the inverse-square law had been discussed. But not only with Hook. Newton acknowledged the works of quite a few other scientists in the foreword to the book. 

Robert Hook was also known as a rather unpleasant man. Arthur Berry writes about him in his book, A short History of Astronomy...Hooke claimed credit for most of the scientific discoveries of the time.”

Still, Newton’s principles of gravity were without parallels in science at the time. He became one of the most important scientists ever. And together with a few others like Einstein, Galilei, da Vince, Tesla, one of the most famous.

What remains is that it was Newton who mathematically described and explained the one single natural law that keeps us all together. The law of attraction between bodies. 

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Yes and no. We can not know if he was hit on the head or if he just saw the apple. We do not know if it was an apple or another fruit, or something else altogether… Or if nothing fell at all. But it’s a very good story. 

Stars in the universe
Courtesy of Jônatas Cunha



The Independent / Newton’s apple

History channel / Did an apple really fall on Isaac Newton’s head?

Wikipedia / Newton’s law of universal gravitation