galileo tower experiment

• Testimonials
• Publications
• Class Schedule
• Terms and Conditions
• JC Syllabus
• IP/Secondary

Understanding Galileo’s Leaning Tower of Pisa Experiment

The image of Galileo Galilei dropping objects from the top of the Leaning Tower of Pisa is one of the most iconic scenes in the history of science. This legendary experiment, often depicted as a pivotal moment in the development of modern physics, is shrouded in myth and misconception.

In this article, we delve into the fascinating story behind Galileo’s Leaning Tower of Pisa experiment, exploring its significance, methodology, and enduring legacy.  

The Historical Context

Galileo Galilei, born in Pisa, Italy, in 1564, was a pioneering astronomer, physicist, and mathematician whose work revolutionalised our understanding of the natural world. In the past, the prevailing Aristotelian view held that the speed at which objects fell was proportional to their weight: heavier objects were believed to fall faster than lighter ones.

Galileo, however, challenged this Aristotelian dogma through a series of thought experiments and empirical investigations. His quest to unravel the mysteries of motion and gravity ultimately led him to conduct the legendary experiment atop the Leaning Tower of Pisa.

The Experiment

Contrary to popular belief, Galileo did not actually drop objects from the Leaning Tower of Pisa. Instead, he described a hypothetical experiment involving the simultaneous release of two objects of different masses from the same height.

According to Galileo’s revolutionary insight, all objects (assuming there is no air resistance) should fall with the same acceleration due to gravity, regardless of their mass.

Imagine two objects—one heavier and the other lighter—to be connected by a string. If Aristotelian assumptions are true, the heavier object falls faster, causing the string to be pulled taut. Logically, this tension should reduce the heavier object’s acceleration.

However, based on Aristotelian assumptions, the entire system (heavy and light objects together) should fall faster than any individual ball.

Due to this contradiction, Galileo surmised that all objects, in the absence of air resistance, should reach the ground at the same time.

The Significance

Galileo’s Leaning Tower of Pisa experiment symbolises the triumph of empirical observation and scientific inquiry over dogma and tradition. By challenging the prevailing beliefs of his time and subjecting them to rigorous experimentation, Galileo paved the way for the scientific revolution and the emergence of modern physics.

Moreover, Galileo’s insights into the laws of motion and gravity laid the groundwork for Isaac Newton’s groundbreaking work on the laws of motion .

Legacy and Misconceptions

While Galileo’s Leaning Tower of Pisa experiment has become synonymous with his scientific legacy, it is essential to dispel some common misconceptions surrounding the experiment. Contrary to popular belief, Galileo did not actually conduct the experiment as depicted in many historical accounts. Instead, it is likely that he only described a hypothetical scenario to illustrate his ideas about the nature of motion and gravity.

Furthermore, the Leaning Tower of Pisa experiment was not the primary catalyst for Galileo’s rejection of Aristotelian physics. Rather, it was one of many empirical investigations that contributed to his broader challenge to the Aristotelian worldview.

Galileo’s Leaning Tower of Pisa experiment remains a symbol of scientific curiosity, ingenuity, and the relentless pursuit of knowledge. While the experiment itself may be more myth than historical reality, its significance lies in its role as a metaphor for the power of observation, experimentation, and critical thinking in advancing our understanding of the natural world.

As we reflect on Galileo’s legacy, we are reminded of the importance of questioning assumptions, challenging orthodoxy, and embracing the spirit of inquiry that drives scientific progress. Galileo’s Leaning Tower of Pisa experiment serves as a timeless reminder of the transformative power of science to illuminate the mysteries of the universe and inspire generations of future scientists and thinkers.

If you’re interested in learning more about physics principles and problems, consider joining our O Level and IP physics tuition in Singapore . Under the guidance of our physics tutor , you are sure to develop a greater understanding of the world around you and ace your exams in the future.

TuitionPhysics

Copyright: Best Physics Tuition™ Centre. All Rights Reserved | User Sitemap

Every print subscription comes with full digital access

Science News

Galileo’s famous gravity experiment holds up, even with individual atoms.

Different types of atoms fall with the same acceleration due to gravity

Individual atoms fall at the same rate due to gravity, scientists report, reaffirming a concept called the equivalence principle.

vchal/iStock/Getty Images Plus

Share this:

By Emily Conover

October 28, 2020 at 6:00 am

According to legend, Galileo dropped weights off of the Leaning Tower of Pisa, showing that gravity causes objects of different masses to fall with the same acceleration. In recent years, researchers have taken to replicating this test in a way that the Italian scientist probably never envisioned — by dropping atoms.

A new study describes the most sensitive atom-drop test so far and shows that Galileo’s gravity experiment still holds up — even for individual atoms. Two different types of atoms had the same acceleration within about a part per trillion, or 0.0000000001 percent, physicists report in a paper in press in Physical Review Letters .

Compared with a previous atom-drop test, the new research is a thousand times as sensitive. “It represents a leap forward,” says physicist Guglielmo Tino of the University of Florence, who was not involved with the new study.

Researchers compared rubidium atoms of two different isotopes, atoms that contain different numbers of neutrons in their nuclei. The team launched clouds of these atoms about 8.6 meters high in a tube under vacuum. As the atoms rose and fell, both varieties accelerated at essentially the same rate, the researchers found.

In confirming Galileo’s gravity experiment yet again, the result upholds the equivalence principle, a foundation of Albert Einstein’s theory of gravity, general relativity. That principle states that an object’s inertial mass, which determines how much it accelerates when force is applied, is equivalent to its gravitational mass, which determines how strong a gravitational force it feels. The upshot: An object’s acceleration under gravity doesn’t depend on its mass or composition.

So far, the equivalence principle has withstood all tests. But atoms, which are subject to the strange laws of quantum mechanics, could reveal its weak points. “When you do the test with atoms … you’re testing the equivalence principle and stressing it in new ways,” says physicist Mark Kasevich of Stanford University.

Kasevich and colleagues studied the tiny particles using atom interferometry, which takes advantage of quantum mechanics to make extremely precise measurements. During the atoms’ flight, the scientists put the atoms in a state called a quantum superposition, in which particles don’t have one definite location. Instead, each atom existed in a superposition of two locations, separated by up to seven centimeters. When the atoms’ two locations were brought back together, the atoms interfered with themselves in a way that precisely revealed their relative acceleration.

Many scientists think that the equivalence principle will eventually falter. “We have reasonable expectations that our current theories … are not the end of the story,” says physicist Magdalena Zych of the University of Queensland in Brisbane, Australia, who was not involved with the research. That’s because quantum mechanics — the branch of physics that describes the counterintuitive physics of the very small — doesn’t mesh well with general relativity, leading scientists on a hunt for a theory of quantum gravity that could unite these ideas. Many scientists suspect that the new theory will violate the equivalence principle by an amount too small to have been detected with tests performed thus far.

But physicists hope to improve such atom-based tests in the future, for example by performing them in space, where objects can free-fall for extended periods of time. An equivalence principle test in space has already been performed with metal cylinders , but not yet with atoms ( SN: 12/4/17 ).

So there’s still a chance to prove Galileo wrong.

More Stories from Science News on Quantum Physics

Physicists measured Earth’s rotation using quantum entanglement

Scientists propose a hunt for never-before-seen ‘tauonium’ atoms 

Two real-world tests of quantum memories bring a quantum internet closer to reality

The neutrino’s quantum fuzziness is beginning to come into focus

A maverick physicist is building a case for scrapping quantum gravity

The development of quantum dots wins the 2023 Nobel prize in chemistry

Clara Sousa-Silva seeks molecular signatures of life in alien atmospheres

Quantum computers could break the internet. Here’s how to save it

Subscribers, enter your e-mail address for full access to the Science News archives and digital editions.

Not a subscriber? Become one now .

• Follow us on Facebook
• Follow us on Twitter
• Follow us on LinkedIn
• Watch us on Youtube
• Audio and video Explore the sights and sounds of the scientific world
• Podcasts Our regular conversations with inspiring figures from the scientific community
• Video Watch our specially filmed videos to get a different slant on the latest science
• Webinars Tune into online presentations that allow expert speakers to explain novel tools and applications
• Latest Explore all the latest news and information on Physics World
• Research updates Keep track of the most exciting research breakthroughs and technology innovations
• News Stay informed about the latest developments that affect scientists in all parts of the world
• Features Take a deeper look at the emerging trends and key issues within the global scientific community
• Opinion and reviews Find out whether you agree with our expert commentators
• Interviews Discover the views of leading figures in the scientific community
• Analysis Discover the stories behind the headlines
• Blog Enjoy a more personal take on the key events in and around science
• Physics World Live
• Impact Explore the value of scientific research for industry, the economy and society
• Events Plan the meetings and conferences you want to attend with our comprehensive events calendar
• Innovation showcases A round-up of the latest innovation from our corporate partners
• Collections Explore special collections that bring together our best content on trending topics
• Artificial intelligence Explore the ways in which today’s world relies on AI, and ponder how this technology might shape the world of tomorrow
• #BlackInPhysics Celebrating Black physicists and revealing a more complete picture of what a physicist looks like
• Nanotechnology in action The challenges and opportunities of turning advances in nanotechnology into commercial products
• The Nobel Prize for Physics Explore the work of recent Nobel laureates, find out what happens behind the scenes, and discover some who were overlooked for the prize
• Revolutions in computing Find out how scientists are exploiting digital technologies to understand online behaviour and drive research progress
• The science and business of space Explore the latest trends and opportunities associated with designing, building, launching and exploiting space-based technologies
• Supercool physics Experiments that probe the exotic behaviour of matter at ultralow temperatures depend on the latest cryogenics technology
• Women in physics Celebrating women in physics and their contributions to the field
• IOP Publishing
• Enter e-mail address
• Show Enter password
• Remember me Forgot your password?
• Access more than 20 years of online content
• Manage which e-mail newsletters you want to receive
• Read about the big breakthroughs and innovations across 13 scientific topics
• Explore the key issues and trends within the global scientific community
• Choose which e-mail newsletters you want to receive

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact [email protected]

Registration complete

Thank you for registering with Physics World If you'd like to change your details at any time, please visit My account

• Opinion and reviews

The legend of the leaning tower

Historians are not sure if Galileo ever carried out experiments at the Leaning Tower of Pisa. So why, asks Robert P Crease, has the story become part of physics folklore?

Commander David R Scott (2 August 1971, lunar surface): “Well, in my left hand I have a feather; in my right hand, a hammer. And I guess one of the reasons we got here today was because of a gentleman named Galileo, a long time ago, who made a rather significant discovery about falling objects in gravity fields. And we thought: ‘Where would be a better place to confirm his findings than on the Moon?’.”

[Camera zooms in on Scott’s hands. One is holding a feather, the other a hammer. The camera pulls back to show the Falcon ­ the Apollo 15 landing craft ­ and the lunar horizon.] Scott: “And so we thought we’d try it here for you. The feather happens to be, appropriately, a falcon feather for our Falcon. And I’ll drop the two of them here and, hopefully, they’ll hit the ground at the same time.” [Scott releases hammer and feather. They hit the ground at about the same time.] Scott: “How about that! Mr Galileo was correct in his findings.”

How the legend started

The finding mentioned by Commander Scott, namely that objects of different mass fall at the same rate in a vacuum, is associated with a single person (Galileo) and a single place ­ the Leaning Tower of Pisa. The culprit is Vincenzio Viviani, Galileo’s secretary in the final years of his life.

We owe many of the Galilean legends to Viviani’s warm biography of the Italian scholar. One is the story of how Galileo climbed the Leaning Tower of Pisa and ­ “in the presence of other teachers and philosophers and all the students” ­ showed through repeated experiments that “the velocity of moving bodies of the same composition, but of different weights, moving through the same medium, do not attain the proportion of their weight as Aristotle decreed, but move with the same velocity”.

In his own books, Galileo uses thought experiments to argue that objects of unequal mass fall together in a vacuum. Without mentioning the Leaning Tower, he reports having “made the test” with a cannonball and a musket ball. What is perhaps surprising, however, is that Galileo found that the two balls did not quite fall together. This finding ­ coupled with the fact that Viviani’s biography is the only source to mention that the experiments were done at the Leaning Tower ­ causes most historians of science to doubt Viviani’s version of what Galileo did. They believe that the elderly and then-blind Galileo may have misremembered when speaking to his youthful assistant.

Dropping the ball

Science historians find Galileo’s early experiments with falling bodies fascinating, for several reasons. One is that Galileo was not the first. As far back as the sixth century, other scholars who doubted Aristotle’s account of motion had also experimented with falling bodies and concluded that Aristotle was wrong. They included several 16th-century Italians and one of Galileo’s predecessors as professor at Pisa.

Also intriguing is Galileo’s report, based on experiment, that balls of unequal weight do not only fall at different rates, but that the lighter one initially pulls ahead of the heavier one until the heavier catches up. In the early 1980s the science historian Thomas Settle tried to repeat Galileo’s falling-body experiments and, astonishingly, noted the same thing. He suggested that fatigue induced in the hand holding the heavier object tends to cause this hand to let go more slowly, even when the dropper believes the objects are released simultaneously.

Yet another fascinating side to Galileo’s experiments is the way that they slowly transformed from genuine scientific inquiries into public displays. After Galileo’s death, scientists including Robert Boyle and Willem ‘sGravesande built air pumps and special chambers to explore vertical fall in evacuated environments. King George III, for instance, once witnessed a demonstration involving a feather and a one-guinea coin falling together inside an evacuated tube. The popularity of such demonstrations continues to this day, featuring in many hands-on science exhibits. Indeed, the “drop stop” at the Boston Museum of Science is currently broken from overuse.

Teachers, no doubt, would call the Apollo “feather-drop” a sloppy experiment. Nobody bothered to measure the height from which the objects were released (probably 110-160 cm). Nobody cared that Scott was leaning over with his arms not parallel to the ground. Nobody measured the time of the fall (on the video it is just above 1 s). But as a demonstration it is unforgettable. The TV coverage ­ plus the fact that it has a webpage with video clip (see related links) ­ makes it possibly the most watched science demonstration ever.

The critical point

So why do falling-body experiments continue to be so popular? They were, for example, voted into the top 10 “most beautiful experiments” of all time in my recent poll of Physics World readers (September 2002 pp19­20). I think the answer is related to the fact that, as everyday experience suggests, heavier bodies do fall faster than light ones. Hammers and golf balls, for example, fall faster than feathers and ping-pong balls. Aristotle had codified this observation into an entire framework that was oriented by the everyday observations he was seeking to explain, involving an agent that exerted a force against resistance. Although this framework fails to incorporate acceleration, it is still the one that we mainly live in and that mainly works for us.

Thus we can still find it enlightening, or even surprising, to see with our very own eyes the expectations of that framework being violated. Galileo played a seminal role in transforming that framework, in developing the abstract thinking involved in the new one, and in illustrating its importance. So what if there was no original experiment? Galileo inspired an entire genre of experiments and demonstrations that allow us to change how we think and see. We might as well refer to these as the offspring of Galileo’s experiment at the Leaning Tower of Pisa.

Want to read more?

Note: The verification e-mail to complete your account registration should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact [email protected] .

• E-mail Address

Physics World Careers

Providing valuable careers advice and a comprehensive employer directory

• Education and outreach

Life after the White Paper

• Art and science

Biff, bang, pow - science takes a knock

Discover more from physics world.

• Astronomy and space

The Wow! signal: did a telescope in Ohio receive an extraterrestrial communication in 1977?

• Everyday science

Researchers cut to the chase on the physics of paper cuts

A breezy tour of what gaseous materials do for us

Related jobs, international marketing manager - uk, publishing services assistant - 12 month ftc, ebooks coordinator, related events.

• Medical physics | Workshop ISMRM Workshop on Motion Correction in MR 3—6 September 2024 | Québec City, Canada
• Particle and nuclear | Symposium World Nuclear Symposium 2024 4—6 September 2024 | London, UK
• Mathematics and computation | Conference Unlocking the potential: The IMA AI/ML Congress 2024 4—5 September 2024 | Birmingham, UK

Bringing classical physics into the modern world with Galileo’s Leaning Tower of Pisa experiment

Professor of Mechanical and Aerospace Engineering, North Carolina State University

Disclosure statement

Larry M. Silverberg does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

View all partners

If you drop a light object and a heavy object from a tower, which one reaches the ground first? As you may recall from high school physics, this is a trick question. Neglecting air resistance, they both fall the same way and reach the ground at the same time – gravity means that their speeds increase at 9.8 meters per second squared, no matter what their mass.

That’s the premise behind Galileo Galilei’s Leaning Tower of Pisa experiment, a classic thought experiment in the field of dynamics.

Dynamics is the physics specialization that studies motion and force. A “dynamicist,” one who studies dynamics, can do everything from improve a basketball player’s free throw to help design spacecraft for interstellar travel .

As a dynamicist , I’ve spent much of my career helping students make sense of modern dynamics. The Leaning Tower of Pisa experiment is one good way to do this. It can explain how classical mechanics – the field that engineers and educators employ every day – was brought into the modern world.

Galileo’s Leaning Tower of Pisa experiment

The Leaning Tower of Pisa experiment led to the curious realization that objects fall with the same accelerations regardless of their mass. But what happens when you place objects of different masses on a smooth table and push each of them with the same force?

Even without accounting for friction , the objects’ accelerations are now different. The lighter objects accelerate more than the heavy ones. When falling, their accelerations are the same, yet when sliding, they’re different.

Let’s now place the two objects in orbit . Imagine one of them is the Sun and the other is the Earth. In classical mechanics, the Sun exerts a force on the Earth equal in magnitude to the force that the Earth exerts back on the Sun.

But the Sun is huge compared with the Earth . Shouldn’t the magnitude of the larger object’s force be larger? And while we’re at it, how would the magnitude of the Sun’s force on the Earth come to be equal to the magnitude of the Earth’s force on the Sun?

Heavy and light objects have equal accelerations when falling but different accelerations when sliding, and objects in space exert equal gravitational forces on each other despite having different masses. This all seems inconsistent, and a little confusing, right?

Modern mechanics

The problems above came from an ambiguity in the concept of force in classical mechanics. In classical mechanics, the force is an interaction between two objects, involving both objects. The magnitudes of the gravitational forces by the Sun and by the Earth depend on the masses of both bodies. The force was never just by the Sun or just by the Earth without regard to the other.

But modern mechanics – the physics of light, atoms, quantum mechanics and curved space-time – changed this concept of force. The modern force by the Sun and the modern force by the Earth are two separate forces, and they depend only on their own masses, excluding relativistic effects .

In modern mechanics, the force is now an action by an object , not an interaction between them. It is viewed as a force field that radiates outward from its source, whose magnitude grows smaller the farther it is from its source. Modern mechanics is a field theory – it deals with objects and the accelerations their force fields create.

So, what happened to the interaction force? Was it discarded? The answer is no, but it is no longer the most fundamental definition of force, either. In modern mechanics, the interaction force, represented by the letter F, is defined in terms of the action force field, represented by the letter P. The interaction force is now the action force P times the mass m on which P acts, so F = mP.

Newton’s second law of motion , a fundamental part of classical mechanics, sets the interaction force F by an object equal to the mass m on which the object acts multiplied by its acceleration, so F = ma. The modern version sets the action force P by an object equal to the other object’s acceleration, so P = a. When multiplying P = a by m we get back F = ma.

Notice it was not about the math in classical mechanics being wrong – but more about the fundamental force being an action force and not an interaction force.

The modern thinking

The modern thinking reinterprets Galileo’s Leaning Tower of Pisa experiment , the sliding blocks, the orbiting of the Earth around the Sun – and interactions in general.

In Galileo’s Leaning Tower of Pisa experiment, the light and heavy objects were falling due to the Earth’s action force, which does not depend on the masses of the falling objects, so their accelerations are naturally the same.

The light and heavy objects sliding on the smooth table were acted on by the same interaction forces. But the fundamental forces – the action forces – are different, so their accelerations are naturally different, too.

In the orbiting of the Earth around the Sun, the action forces by the Sun and by the Earth are no longer equal. The action force by the Sun, with its huge mass, is proportionally larger than the force by the Earth – as intuition suggests.

Science takes many years to evolve as it edges closer to revealing the nature of reality. One sees this in the evolution that led to modern mechanics – where scientists now embrace a theory of force fields that predicts the dynamics of objects, despite it being almost against common sense.

• History of science
• Isaac Newton
• Field theory

Chief Financial Officer

Director of STEM

Community member - Training Delivery and Development Committee (Volunteer part-time)

Chief Executive Officer

Head of Evidence to Action

• Exhibitions
• Handicrafts
• Cinema and TV
• Ancient art
• '800 e '900
• Contemporary art
• AB Arte Base
• All reviews
• Mostre in corso
• Mostre concluse
• North Italy
• Center Italy
• South Italy
• Islands of Italy
• Foreign countries
• Exhibition finder

Between science and legend, Galileo's experiment from the Tower of Pisa

The bell tower of the Primatial Cathedral of Santa Maria Assunta in Pisa , universally known as the Leaning Tower , is the symbol of the city and of Italy in general, its fame is boundless, and it is also said to have been the celebrated stage and laboratory of an important experiment by the Pisan scientist Galileo Galilei .

This is the experiment of the gravi or the fall of the gravi , about which it is still debated today whether it was actually carried out, or rather attested to as mere mental speculation. The experiment took its starting point from a theorization of Aristotle , the philosopher who in fourth-century B.C.E. Athens had formulated explanations to numerous physical phenomena; among them, one of his fundamental propositions was that there is no effect without a cause, and by extension, therefore, there is no motion without a force to act upon it. Aristotle argued that the speed of an object is proportional to the driving force and inversely proportional to the resistance of the medium.

Applying these ideas to falling bodies, the philosopher ended up concluding that different bodies fall at different speeds , and more specifically, the greater the weight, the greater the speed of fall. This is a statement that is consistent with the phenomenon actually observed, and it remained conviction for a very long time, and still enjoys great fortune today.

But in fact it was an erroneous theory that was criticized repeatedly, as early as the sixth century AD by the Byzantine philosopher John Philoponus, and then more veminently in the sixteenth and seventeenth centuries as the science of motion became more and more advanced. Already the intellectual Benedetto Varchi had questioned the Aristotelian idea in 1544 when he published his treatise Questione sull’alchimia : “[...] although the custom of modern philosophers is always to believe, and never to prove everything, which is written in good authors, and especially in Aristotle, it is not, however, that it was not and safer, and more delightful to do otherwise, and to descend sometimes to experience in some things, as verbi gratia in the movement of serious things, in which thing and Aristotle, and all the other Philosophers without ever doubting it have believed, et affirmed that the more serious a thing is, the more quickly it descends, which proof proves not to be true. [...]”.

One must wait, however, for Galileo Galilei to see the Aristotelian view definitively refuted. The then young scientist held the chair in mathematics at the University of his city between 1589 and 1592, and as a teacher he immediately showed his pedagogical approach contrary to dogma: “The method we shall follow will be to make what is said depend on what is said, without ever supposing as true what is to be explained. This method was taught to me by my mathematicians, while it is not observed enough by certain philosophers when they teach physical elements.... Consequently those who learn, never know things from their causes, but believe them only by faith, that is, because Aristotle said them. If then it will be true what Aristotle said, there are few who investigate; it is enough for them to be thought more learned because they have more Aristotelian texts on their hands [...] that a thesis is contrary to the opinion of many, I do not care at all, as long as it corresponds to experience and reason.”

And it was during his Pisan period that Galilei composed De motu antiquiora . In the text, which remained in manuscript form for a long time, and was not given to print until the 19th century, Galilei put together his lectures that had as their theme the problem on motion, beginning to flesh out his formulations on the theory of gravities . It is still debated today whether this was just a mental exercise or whether, as the story goes, he actually tried it out by taking the Tower of Pisa as his laboratory.

Fuelling the thesis of the experiment was Vincenzo Viviani , his favorite disciple and biographer who writes about it in his work Racconto istorico della vita di Galileo Galilei : “et allora, to the great dismay of all philosophers, were convinced by it of falsehood, by means of experience and with firm demonstrations and discourses, many conclusions of the same Aristotle concerning the matter of motion, until that time held to be very clear et indubitable; as, among others, that the velocities of furniture of the same matter, unequally grave, moving by the same means, do not otherwise preserve the proportion of the gravities them, assigned to them by Aristotle, rather that they all move with equal velocity, proving this by replicated experiments, made from the height of the Campanile of Pisa with the intervention of the other readers and philosophers and of the whole schoolchildren; and that neitherless the velocities of the same mobile for different means retain the reciprocal proportion of the resistances or densities of the same means, inferring this from manifest absurdities which in consequence would follow against the same sense.”

But the famous experiment with the “gravi,” which both tradition and biographer would have it performed from the Tower of Pisa , is almost unanimously believed to be a mere legend , and even if it had been carried out it would have apparently refuted the Galilean thesis since, as already consciously noted by Galileo himself, “only a space entirely vowed to air and every other body” could prove the truth of what he claimed , but at that time there were neither spaces nor pumps capable of subtracting air resistance. Although such an experiment was not feasible at that time, the scientist could investigate the phenomenon with different approaches using logic and also empirically .

Galileo, who argued that different weights fall at the same rate, conducted a happy lucubration that challenged the Aristotelian formulation, as there were inherent contradictions in the latter that the Pisan scientist pointed out. Assuming Aristotle’s theory to be true, that is, that a light body falls more slowly than a heavier one, in the event that they were bound together, they would have to fall at the average speed between the two, since the heavy object would be slowed down by the light one. But at the same time, adding the two bodies together would result in an even heavier third, and thus its falling motion should be accelerated. This paradox, with an obvious contradiction between the falling times, leads one to consider the Aristotelian assumption impossible and therefore erroneous.

Galileo would later remark on the concept in an experiment he claimed to have performed, comparing the fall of an artillery ball and a musket ball. And which, for simplicity’s sake, we summarize using units of measurement different from those proposed by Galileo. Imagine that the artillery ball is ten times heavier than the bullet; thrown at the same time from the same height of 100 meters, according to the Aristotelian formula, the heavier one should touch the ground when the bullet would have traveled only ten meters. Instead, Galileo pointed out that the distance of arrival on the ground between the two was minimal.

While it was impossible for Galileo to perform the “gravi” experiment correctly in his day, several centuries later, in 1971, astronaut Dave Scott reiterated it in a form of great scenic impact : during the mission carried out by Apollo 15, as he stepped on the lunar surface, he let a hammer and a feather fall at the same time, which hit the ground at the same time, due to the absence of atmosphere, proving that the Pisan scientist was not wrong at all.

Warning: the translation into English of the original Italian article was created using automatic tools. We undertake to review all articles, but we do not guarantee the total absence of inaccuracies in the translation due to the program. You can find the original by clicking on the ITA button. If you find any mistake, please contact us .

Most read of the month

Today, we ask how fast things fall, and we rewrite science. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

W hen Galileo was young, one of his contemporaries used these words to describe Aristotle's idea of how objects fall:

There is a natural place for everything to seek, as: Heavy things go downward, Fire upward, And rivers to the sea.

Galileo took an interest in rates of fall when he was about 26 years old and a math teacher at the University of Pisa. It seemed to him that -- with no air resistance -- a body should fall at a speed proportional to its density. He decided to test this modified Aristotelian view by making an experiment.

There was no tradition of describing experimental research in Galileo's day. Controlled experiments were almost unknown. So Galileo's report was pretty skimpy. He seems to have dropped different balls from a tower. But what weights? What tower? We can be pretty sure it was the Leaning Tower of Pisa. But we end up doubting whether or not he really did the experiment. Maybe he just reported what he thought should have happened.

One result of the experiment surprised Galileo, and one surprises us. Galileo found that the heavy ball hit the ground first, but only by a little bit. Except for a small difference caused by air resistance, both balls reached nearly the same speed. And that surprised him. It forced him to abandon Aristotelian ideas about motion. If he really did the experiment, it was surely a turning point in the history of science.

But what surprises us is what Galileo says happened just after he released the two balls. He says the lighter ball always started out a little bit faster than the heavy ball. Then the heavy ball caught up. That sounds crazy.

So Thomas Settle and Donald Miklich reran Galileo's tower experiment in front of a camera. An assistant held four-inch iron and wooden balls at arm's length -- as Galileo would have to have held them to clear the wide balustrate atop the Pisa tower. It turns out that when you try to drop them both at once, your strained muscles fool you. You consistently let go of the lighter one, the one you've been gripping less intensely, first. That means Galileo accurately reported what he seen happening. And we're left with no doubt that he actually did do the experiment. Galileo went on to become the first real challenger of Aristotle. His tower experiment was no fable -- no apple falling on Newton's head. This was one of the first controlled scientific experiments. Like most of today's experiments, it was imperfect. But this experiment changed Galileo, and it changed history. I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Settle, T. B., Galileo and Early Experimentation, Springs of Scientific Creativity , (F. Aris, H.T. Davis, and R.H. Stuewer, eds.). Minneapolis: University. of Minnesota Press, 1983, pp. 3-20.

• Engines Transcripts
• Search Episodes by Keyword
• Airing schedule for HPM

AmazingPhysicsForAll

Experiments

You may watch the summary of this post here as video here.

Galileo ‘s legendary experiment from the Leaning Tower of Pisa in the 16th century to demonstrate the nature of falling objects.

Consider two iron balls. Assume one ball weighs 5 kgs, and the other ball weighs 10 Kgs. When we drop these two iron balls from the same height at the same time, which one hits the ground first? The heavier one or the lighter one?

Our intuition may say that the heavier one hits the ground first. Even Aristotle, the Greek Philosopher, thought the same way. But in reality, both the iron balls reach the ground at the same time. How is that possible? Keep reading.

Aristotle's Doctrine

Aristotle (384-322 BC), the Greek philosopher, claimed that heavy objects would fall faster.

                “There is a natural place for everything to seek as:

                Heavy things go downward, Fire upward,

                And rivers to the sea.”

Cannon Balls Experiment

As a staunch proponent of scientific method, Galileo (1564 – 1642 AD) wanted to check this out. (See his quote on the picture above.) Legend goes that he dropped two cannon balls (of different masses) simultaneously from the to top of the leaning tower of Pisa and observed the result.

The result was: Both the cannon balls hit the ground at the same time. Evidently, what Aristotle claimed did not happen. 

How do we explain this result? Keeping our intuition aside, once we look into the equations that describe the motion of objects under constant acceleration, it is easy to understand the result.

Free Fall Equation

Here is the equation that determines the time a freely falling object takes to reach the ground when it is dropped from a height, say, s.

In the above equation, t stands for the time taken by the object to reach the ground, s is the height, and g is the acceleration due to gravity.

The fact stands out clearly from this equation. The time (t) depends on s and g, and there is no dependency on mass . When we drop two objects simultaneously from the same height in a given place, both s and g turn out to be same for both the falling objects. So, the time (t) will be the same for both objects despite their masses being different.

Therefore, two objects with different masses will reach the ground at the same time when they are dropped simultaneously from the same height in a given place.

If you are curious to know how we got the above equation, click here .

What about a Feather?

When we drop a feather and an iron ball simultaneously from some height, why does a feather take more time to hit the ground? This is a valid question.

This is because the weight of the feather is tiny compared with the drag force acting on it. The drag force is able to quickly stabilize its descending speed, and the feather comes down slowly with a constant speed. However, in the case of an iron ball, the weight of the iron ball is too big to get controlled or reduced significantly by the drag force, and the iron ball keeps on accelerating until it hits the ground.

In fact, if you drop a feather and an iron ball in vacuum, both will hit the bottom at the same time.

Galileo's Leaning Tower of Pisa experiment

Between 1589 and 1592,[1] the Italian scientist Galileo Galilei (then professor of mathematics at the University of Pisa) is said to have dropped two spheres of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass, according to a biography by Galileo's pupil Vincenzo Viviani, composed in 1654 and published in 1717.[2][3]:19–21[4][5]

According to the story, Galileo discovered through this experiment that the objects fell with the same acceleration, proving his prediction true, while at the same time disproving Aristotle's theory of gravity (which states that objects fall at speed proportional to their mass). Most historians consider it to have been a thought experiment rather than a physical test.[6] Galileo's experiment

At the time when Viviani asserts that the experiment took place, Galileo had not yet formulated the final version of his law of free fall. He had, however, formulated an earlier version which predicted that bodies of the same material falling through the same medium would fall at the same speed.[3]:20 This was contrary to what Aristotle had taught: that heavy objects fall faster than the lighter ones,and in direct proportion to their weight.[3]:9[7] While this story has been retold in popular accounts, there is no account by Galileo himself of such an experiment, and it is accepted by most historians that it was a thought experiment which did not actually take place.[8][9] An exception is Stillman Drake, who argues that it took place, more or less as Viviani described it, as a demonstration for students.[3]:19–21, 414–416

Galileo set out his ideas about falling bodies, and about projectiles in general, in his book Two New Sciences. The two sciences were the science of motion, which became the foundation-stone of physics, and the science of materials and construction, an important contribution to engineering. Galileo arrived at his hypothesis by a famous thought experiment outlined in his book On Motion.[10] This experiment runs as follows: Imagine two objects, one light and one heavier than the other one, are connected to each other by a string. Drop this system of objects from the top of a tower. If we assume heavier objects do indeed fall faster than lighter ones (and conversely, lighter objects fall slower), the string will soon pull taut as the lighter object retards the fall of the heavier object. But the system considered as a whole is heavier than the heavy object alone, and therefore should fall faster. This contradiction leads one to conclude the assumption is false. Other performances The Nieuwe Kerk in Delft, where the experiment by Stevin and de Groot took place

A similar experiment took place some years earlier in Delft in the Netherlands, when the mathematician and physicist Simon Stevin and Jan Cornets de Groot (the father of Hugo de Groot) conducted the experiment from the top of the Nieuwe Kerk. The experiment is described in Simon Stevin's 1586 book De Beghinselen der Weeghconst (The Principles of Statics), a landmark book on statics:

Let us take (as the highly educated Jan Cornets de Groot, the diligent researcher of the mysteries of Nature, and I have done) two balls of lead, the one ten times bigger and heavier than the other, and let them drop together from 30 feet high, and it will show, that the lightest ball is not ten times longer under way than the heaviest, but they fall together at the same time on the ground. (...) This proves that Aristotle is wrong.[11][12][13]

File:Apollo 15 feather and hammer drop.ogvPlay media Hammer and Feather Drop by astronaut David Scott, Apollo 15 (1.38 MB, ogg/Theora format)

Astronaut David Scott performed a version of the experiment on the Moon during the Apollo 15 mission in 1971, dropping a feather and a hammer from his hands. Because of the negligible lunar atmosphere, there was no drag on the feather, which hit the ground at the same time as the hammer. See also

Terminal velocity (An object dropped through air from a sufficient height will reach a steady speed, called the terminal velocity, when the aerodynamic drag force pushing up on the body balances the gravitational force (weight) pulling the body down.) Nordtvedt effect Newton's second law Law of Inertia

Some contemporary sources speculate about the exact date; e.g. Rachel Hilliam gives 1591 (Galileo Galilei: Father of Modern Science, The Rosen Publishing Group, 2005, p. 101). Vincenzo Viviani (1717), Racconto istorico della vita di Galileo Galilei, p. 606: [...dimostrando ciò con replicate esperienze, fatte dall'altezza del Campanile di Pisa con l'intervento delli altri lettori e filosofi e di tutta la scolaresca... [...Galileo showed this [all bodies, whatever their weights, fall with equal speeds] by repeated experiments made from the height of the Leaning Tower of Pisa in the presence of other professors and all the students...]. Drake, Stillman (2003). Galileo at Work: His Scientific Biography (Facsim. ed.). Mineola (N.Y.): Dover publ. ISBN 9780486495422. "Sci Tech : Science history: setting the record straight". The Hindu. June 30, 2005. Retrieved May 5, 2009. Vincenzo Viviani on museo galileo "El experimento más famoso de Galileo probablemente nunca tuvo lugar". The Conversation. May 16, 2019. Retrieved May 17, 2019. Sharratt, M. (1994). Galileo: Decisive Innovator. Cambridge University Press. p. 31. ISBN 0-521-56671-1. Groleau, R. (July 2002). "Galileo's Battle for the Heavens". Ball, P. (30 June 2005). "Science history: Setting the record straight". The Hindu. Van Helden, Albert (1995). "On Motion". The Galileo Project. Laet nemen (soo den hoochgheleerden H. IAN CORNETS DE GROOT vlietichste ondersoucker der Naturens verborghentheden, ende ick ghedaen hebben) twee loyen clooten d'een thienmael grooter en swaerder als d'ander, die laet t'samen vallen van 30 voeten hooch, op een bart oft yet daer sy merckelick gheluyt tegen gheven, ende sal blijcken, dat de lichste gheen thienmael langher op wech en blijft dan de swaerste, maer datse t'samen so ghelijck opt bart vallen, dat haer beyde gheluyden een selve clop schijnt te wesen. S'ghelijcx bevint hem daetlick oock also, met twee evegroote lichamen in thienvoudighe reden der swaerheyt, daerom Aristoteles voornomde everedenheyt is onrecht. In: Simon Stevin, De Beghinselen der Weeghconst, 1586. Asimov, Isaac (1964). Asimov's Biographical Encyclopedia of Science and Technology. ISBN 978-0385177719

E. J. Dijksterhuis, ed., The Principal Works of Simon Stevin. Amsterdam, Netherlands: C. V. Swets & Zeitlinger, 1955 vol. 1, pp. 509, 511.

Further reading

Adler, Carl G. (1978). "Galileo and the Tower of Pisa experiment". American Journal of Physics . 46 (3): 199–201. Bibcode:1978AmJPh..46..199A. doi:10.1119/1.11165. Crease, Robert P. (2006). "The Legend of the Leaning Tower". In Hall, Linley Erin (ed.). The laws of motion : an anthology of current thought. Reprint of an article in Physics World , February 2003. (1st ed.). New York: Rosen Pub. Group. pp. 8–14. ISBN 9781404204089. Segre, Michael (1989). "Galileo, Viviani and the tower of Pisa". Studies in History and Philosophy of Science Part A. 20 (4): 435–451. doi:10.1016/0039-3681(89)90018-6.

External links

Galileo experiment on the Moon Galileo and the Leaning Tower of Pisa The Hammer-Feather Drop in the world’s biggest vacuum chamber

Physics Encyclopedia

Hellenica World - Scientific Library

Retrieved from "http://en.wikipedia.org/" All text is available under the terms of the GNU Free Documentation License