See Galileo’s Famous Gravity Experiment Performed in the World’s Largest Vacuum Chamber, and on the Moon

It is one of the most famous exper­i­ments in all of sci­ence his­to­ry, but there’s sig­nif­i­cant doubt about whether it actu­al­ly took place. Did Galileo drop objects of dif­fer­ing mass from the Lean­ing Tow­er of Pisa in 1589 to demon­strate the the­o­ries pro­posed in his unpub­lished text De motu (“Of Motion”)? Rice University’s Galileo Project notes that schol­ars have long thought Galileo’s ref­er­ences to exper­i­ments he con­duct­ed “were only rhetor­i­cal devices.” As PBS’s NOVA writes, “it’s the kind of sto­ry that’s easy to imag­ine, easy to remem­ber, but whether he ever per­formed the exper­i­ment at the tow­er is debat­able.” That’s not to say Galileo didn’t test any of his ideas while he taught at the Uni­ver­si­ty of Pisa dur­ing 1589 and 1592, only that his most famous the­o­ry about the effects of grav­i­ty on free-falling objects rests main­ly on a con­cep­tu­al thought exper­i­ment.

In fact, it would have been impos­si­ble for Galileo to ful­ly demon­strate his the­o­ry because of the effects of air resis­tance. Sub­tract the atmos­phere, how­ev­er, and we can eas­i­ly con­firm Galileo’s hypoth­e­sis that any two objects, regard­less of weight, shape, or mate­r­i­al of com­po­si­tion, will fall at exact­ly the same rate when dropped. One of the most mem­o­rable times this exper­i­ment did take place was not in Italy or any­where else on earth, but on the Moon, when astro­naut David Scott, com­man­der of the Apol­lo 15 mis­sion, dropped a geo­log­ic ham­mer and a falcon’s feath­er at the same time in 1971 (above).

As cool as Com­man­der Scott’s exper­i­ment is, it’s still not as dra­mat­ic as the ver­sion of the exper­i­ment at the top of the post, con­duct­ed at NASA’s Space Pow­er Facil­i­ty in Ohio in the world’s largest vac­u­um cham­ber. A great deal of the dra­ma comes cour­tesy of physi­cist Bri­an Cox, who presents the exper­i­ment for BBC Two’s Human Uni­verse, explain­ing the his­to­ry and con­struc­tion of the vac­u­um cham­ber, which sim­u­lates the con­di­tions of out­er space. Then we’ve got the mul­ti­ple cam­era angles and dra­mat­ic music… typ­i­cal TV show stuff, effec­tive nonethe­less at set­ting us up for the big drop. Even though we “know how the exper­i­ment will end,” points out io9, and may have seen it per­formed before—on the Moon even—this demon­stra­tion is some­thing spe­cial.

First, we get an anti­cli­mac­tic drop of the objects—a bowl­ing ball and a feather—while the cham­ber is still full of air. As expect­ed, the ball plum­mets, the feath­ers gen­tly drift. Then, in a sequence right out of a sci-fi film, engi­neers seal off the enor­mous cham­ber, and the three-hour removal of air is tele­scoped into a few sec­ond mon­tage of push­ings of but­tons and mum­blings into inter­coms. What hap­pens next will… well, you know the click­bait ver­biage. But it cer­tain­ly sur­pris­es Cox and a room­ful of NASA engi­neers. Cox goes on to explain, using Einstein’s the­o­ry of gen­er­al rel­a­tiv­i­ty, that the rea­son the objects fall at the same rate is “because they’re not falling; they’re stand­ing still.” The sci­ence may be com­mon knowl­edge, but see­ing it in action is indeed pret­ty mind blow­ing.

Relat­ed Con­tent:  

An Ani­mat­ed His­to­ry of Physics Intro­duces the Dis­cov­er­ies of Galileo, New­ton, Maxwell & Ein­stein

Galileo’s Moon Draw­ings, the First Real­is­tic Depic­tions of the Moon in His­to­ry (1609–1610)

Bohemi­an Grav­i­ty: String The­o­ry Explored With an A Cap­pel­la Ver­sion of Bohemi­an Rhap­sody

Free Online Physics Cours­es

Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness


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Comments (4)
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  • Judy Robertson says:

    It may be physics, but to me it’s close to mag­ic. Won­der­ful video

  • Lokesh Lakudkar says:

    I am very thank­ful to the whole team of NASA for this exper­i­ment. In this exper­i­ment, I have a lit­tle query which is as fol­lows;

    In the first exper­i­ment, bowl­ing ball and feath­er (both hav­ing dif­fer­ent mass­es) dropped from same height in pres­ence of air and earth grav­i­ty.

    Result: Bowl­ing ball dropped first because of it’s mass; which is more than feath­er and oppo­site air force act on ball; which oppose the weight of ball but it is neg­li­gi­ble as com­pared to weight of ball.
    &
    Feath­er dropped last because of it’s less mass than bowl­ing ball and oppo­site air force; which resist it’s accel­er­a­tion. So it took more time.

    But Sec­ond exper­i­ment, In vac­u­um envi­ron­ment, both takes same time to fall down.

    Now my query is:

    If both hav­ing dif­fer­ent mass­es, so accel­er­a­tion will also be dif­fer­ent in vac­u­um also.
    Air only resists the accel­er­a­tion of feath­er but it can not effect the weight of body in vac­u­um and in same earth grav­i­ty.

    So, How it is pos­si­ble?

  • Lokesh Lakudkar says:

    I mean If both hav­ing dif­fer­ent mass­es, so weight will also be dif­fer­ent in vac­u­um also.
    Air only resists the accel­er­a­tion of feath­er but it can not effect the weight of body in vac­u­um and in same earth grav­i­ty.

    So, How it is pos­si­ble?

    Kind­ly give me reply with prin­ci­ple, which is applic­a­ble on this exper­i­ment.

  • Lokesh Lakudkar says:

    I mean, If both hav­ing dif­fer­ent mass­es, so weight of bod­ies will be dif­fer­ent in vac­u­um also.
    Air only resists the accel­er­a­tion of feath­er but it can not effect the weight of body in vac­u­um and in same earth grav­i­ty.

    So, How it is pos­si­ble?

    Kind­ly give the reply with applic­a­ble prin­ci­ple.

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