Episode 172: Newton’s Crane Cradle

Air Date: October 5, 2011

It is possible to construct a working Newton’s cradle using wrecking balls. (Inspired by a viral video.)

busted

Adam and Jamie decided to start with small-scale testing and work their way up to find any flaws. To determine the efficiency of energy transfer from ball to ball, Adam pulled the ball at one end out to a certain distance and measured the length of the swing at the other end. Their first three models—an off-the-shelf desktop toy, and two built with 2.5 and 6 in (64 and 152 mm) solid steel bearings—gave 98%, 97%, and 94% efficiency, respectively. Jamie noted that the energy loss increased at the larger scales, but did not depend directly on size or mass.

To simulate miniature wrecking balls, Adam and Jamie filled five 6 in (152 mm) hollow steel spheres with plaster that had properties similar to concrete. This version gave only 63% efficiency, but Jamie suggested putting a steel plate through the center of each ball to reduce energy transfer into the concrete. They then built five 2,000 lb (907 kg) balls by cutting hollow naval buoys in half, sandwiching a steel plate in each, and filling the space with rebar and concrete. When the rig was assembled at Mare Island Naval Shipyard and hung from an I-beam frame, it gave very poor efficiency and quickly stopped swinging, even after each ball was hung from two cables rather than one as shown in the video. Noting the increased potential for energy losses at large scales, Adam and Jamie declared the myth busted, then later learned that the original video had been faked.

A car balanced on the edge of a cliff can topple over if a bird perches on the front end.

busted

The Build Team set up a shipping container as a cliff, with a dirt escape ramp built up against its edge so that the test car would roll down safely if it went over the edge. Grant and Tory, in the car, eased it forward to find the balance point; after several tries and the use of a forklift and straps on the rear bumper, they were able to get the car balanced.

With Grant and Tory still in the car, various birds were brought in and allowed to perch on the hood. Two pigeons (1 lb (0.45 kg) each), two hawks (2.5 lb (1.1 kg) each), and an eagle owl (7 lb (3 kg)) were tried separately; none were able to do more than wobble the car slightly. Grant commented that although a weight near the front bumper gave a large amount of leverage, the car itself had enough weight to counteract the effect.

The team located a model helicopter and modified it to weigh 20 lb (9.1 kg), the same as a California condor (the largest flying bird in North America). When this too failed to tip the car, the team classified the myth as busted and set out to find out how much weight it would take. The car only tipped after Kari put 80 raw, 1.5 lb (0.7 kg) game hens onto the hood and Tory added a raw, 20 lb (9 kg) remote-controlled turkey for a total of 140 lb (64 kg).

(This myth was revisited in Revenge of the Myths and declared “busted” again.)

32 Comments

  1. Oscar Londono says:

    The small Newton’s cradle worked well, and the conservation of momentum could be observed. However, the experiment did not work when large balls were used. In my opinion, the experiment was not done correctly. It took me just a few seconds to notice that the surfaces of the large metal balls were not smooth. They had many imperfections, especially at those points where they balls made contact. That is one reason why the experiment failed. The energy is dissipated in many directions. We should notice the conservation of momentum even in the collisions of those large balls. The final conclusion should not have been “Busted.”

    • skylar says:

      YOU KNOW IS IT NOT VELOCITY EQEAL MASS EQEAL CANETIC ENERGY.THEY NEEDED TO SORT OF THROW IT AT THE OTHER BALL.

  2. Kevin Barney says:

    You should have tried bowling balls,when i was young I saw a newtons cradle in Seattle made from bowling balls that worked very well. Plus theres nothing like the sound of bowling balls smacking together.

  3. mick beatwell says:

    gravity is the problem,the end ball receiving the shock wave is being pulled downwards as well as the balls not being solid enough.

  4. Tanya Rezutek says:

    you waisted food from putting all that chicken on the hood of that car!! u could have gave that to the poor or someone who needs it!u could have used something else. what a disappointment to see u waist food like that on t.v!!

    • So Dumb says:

      If you are going to criticize other people then at least spell “waste” right.

    • adrian says:

      How about the less fortunate get a job like every one else rather than purchasing drugs, alcohol and cigarettes.

    • fuqthegovt says:

      you sound like a democrat. let the ones too poor or stupid to feed themselves die, the rest will be better off. It’s pointless and even counter-productive to fight social darwinism.

    • David says:

      WASTING FOOD IS SHAMEFUL – El desperdicio de comida es una vergüenza – Gaspiller la nourriture est honteux – Sprecare il cibo è vergognoso – Desperdiçar comida é vergonhoso

      This got to Europe (Spain) only now and I am appalled to see that just one person pointed out how stupid that is.

  5. Rick Hubble says:

    No surprise with Newton’s cradle…on the smaller scale the efficiency dropped from 98% to 96% and then to 94% this means the inefficiency tripled in a short period of time (a significant change in percent without being a significant change in percentage pioints). Still, I too would love to see this done with bowling balls.

  6. Randy says:

    OK folks heres the deal. 1st. Mick was partially correct, Wrecking balls are made of low grade steel. 2nd They are hollow. So when the balls make conact, the type of steel absorbs part of the energy. Second, being hollow the air inside compresses and acts as a damper. think of pushing the sides of a basketball. The air inside compresses. With the air being constrained, the shock wave is forced up/downward. The whole setup and dual line was correct. Recomemndations, utilize a solid steel ball. (bowling balls have been done, but good idea). AS far as the CAR, The CG was behind the tip point, increasing the moment arm to the point it would not tip. Next time Make sure the CG is located at the top point. When you added the passenger and driver back in the car that moment arm shifted further back. So had the CG/Tip point been correct as in some movies, the RC Helo could have tipped the car by landing. Basic Physics guys. GREAT shows tho…

  7. steve says:

    CAR TEETERING OVER A CLIFF…after dropping the car several times on the ” cliff ” im sure the underside had several dents in it , making it nearly impossible to find exact center of ballance , therefore the car would rest at the closest dent , and be not perfectly ballanced…if the car were PERFECTLY BALLANCED , it would teeter back and forth instead of sitting rigidly , and yes , a small bird would make it tip . perfect ballance is a matter of millimeters , not feet , or even inches , you get the car PERFECTLY BALLANCED , and a FLY would make it go….love the show , but it goes to show what ive always known…usually ppl with great ” book smarts ” have no common sense….

    • Matthew says:

      I agree about the car.it is not in exact equilibrium

    • David says:

      Well, I mean Mythbusters is all about simulating it to see if it were possible in real life. It would be virtually impossible to get the right equilibrium. You’d have to be spot on to the nearest fraction of an atom. Getting to that precision would almost be impossible.

      • Stephen says:

        No, it is possible. They put no effort to find the centre of gravity.

        the problem is the mythbusters have a deadline to make, so they shortcut many experiments.
        That’s why I do not find their results conclusive.

  8. mick beatwell says:

    Thanks randy, it’s allways nice to be partially wright rather than partially wrong.

  9. Daisy says:

    Wouldn’t the weight of an a extint Moa bird send it over the cliff?

    • David says:

      If you could do that, they could just throw an ostrich on it. And since birds are technically dinosaurs, they could have put a sauroposeidon on there. Tip the car? More like destroy the whole ramp.

  10. Matthew says:

    The car Is not perfectly balanced ,and not in equilibrium .if it was,dropping a paperclip on it will get it off the cliff

  11. Roger says:

    Having been a fan of your show for many years I have to come to the conclusion that on many of the Myths that you try to “Bust” or “Confirm” you and your team will change the parameters of the Myth to suite your tastes. many times this will rsult in the Myth being busted despite other evidence to the contrary. Case in point…Newtons Cradle…as many people know there are different types of wrecking balls from filled to solid steel varities. I know as many people do the with solid steel balls said experiment could and probably has been done correctly with minimal loss of transferable energy. As we also know when you fill a steel sphere with concrete or any other solid material you will lose alot of your energy. This I guess is why it came up “Busted” for you guys. I still enjoy the show greatly.

    • David says:

      I haven’t heard of wrecking balls that aren’t hollow and are completely steel. That would be wayyyy beyond their budget, and in the video, I think it was certain that the balls they had in the video were filled with cement.

      • Takumi says:

        I just read your blog The Shattering and it made me recall an edipose in my life quite similar. I was 23 yrs old, 7 months pregnant with my second child and just had the millionth fight with my then husband about his addiction, inability to keep a job, and total disregard for his family responsibilities. I was in hysterics, crying, ran out the door, ran four streets away to a small park, sat on a swing and sobbed uncontrollably(in the pouring rain). I thought the rain drowned out my sobs, but a nearby neighbor came out, invited me into their home, a complete stranger, to calm down. I sat awhile, then calmly returned home and continued to live in hell, until I got the strength to leave 5 yrs later. I guess something just snapped inside me thank God for that. I, too, survived, and so did my daughters who are now 37, 33, and 31. Keep on keepin’ on life will get happy and you will be loved!

  12. Gerry Jackson says:

    Not only are ball bearings (used on most desk top Newton’s Cradles) ground smooth, they have been heat treated and hardened to around Rockwell 60 or so. In untreated steel, atoms are free to move about as heat and pressure allow. The hardening process, however, freezes the atoms to the point that the ball absorbs far less energy and therefore allows it to bounce better. Does that make sense? In other words the balls need to be identical in composition high carbon steel, hardened to identical Rockwells, and be ground to identical smoothness. PS I really like the show.

  13. mick beatwell says:

    That reminds me if the allmegolly bird was to shi oops, SIT on the hood would that tip it over the edge, DISSCUSE

  14. Digifan says:

    The car is not balance correctly. Neither is the bird. I think this experiment need more research and more calculations. As others had pointed out the car need to achieve equilibrium. Placing this car on the edge of a steel container is another problem the team must resolve. I vote these experiments need a revisit.

  15. tony says:

    hi,,,i am sory to say that i am certain that the wrecking balls are not solid ,,,they are hollow spheers filled with another material such as sand or cement,,,if you notice there is a fill hole near the bottom,,,it would deaden the shock wave traveling thru it,,,,,newtons ball racks use hardened solid balls which transfer the shock wave thru them because of the same density,,,,in that old movie the balls that were used there were probaly solid forged steel which is a very hard metal,,,,they dont make em like the old days now,,anyway if you check this out you will find it to be true physics,,,cheers everyone,,,merry x mas and a happy new year

  16. tony says:

    as for the bird on the car thing,,,you need a more precice fulcrum,,,a sharp corner against a soft rocker pannel does not make a real good fulcrum point,,,it should be posiable to balence that car to a matter of ounces if there were no outside influences such as wind or moving people inside,,,if it were a sharp edge against a hard surface,,,,would be a lot less resintance,,,

  17. Digifan says:

    We need to bring this critical error to the attention of the team. The wrecking balls are not solid. Neither are the balls in the small scale tests. If we do the calculations we will discover the energy transfer between the balls are equalized. If we apply this principle we will see the surface of the balls will have no effect on the result. Remember Newton’s Laws. We certainly do. It is definitely time for a revisit.

  18. Eric says:

    It did not work because the balls were not solid. Try real wrecking balls. (Wiki) Wrecking balls range from about 1,000 lb to around 12,000 lb (450 kg to 5400 kg). The ball is made from forged steel, which means the steel is not cast into a mold in a molten state. It is formed under very high pressure while the steel is red hot (soft but not molten) to compress and to strengthen it.To simulate small scale what was done on the show use foil over plaster balls and see if that works.

  19. Felix says:

    The balls where linked to a suspended structure that acted as a pendulum it self. Therefore, the problem became one of double pendulum. The momentum of the ball went in th suspended bar also, which explains the collective movement of the balls. This is a simple physics problem. This is what happens when you don’t make the right assumptions in the first hand. These guys are not scentist, Keep that in mind.

  20. Mikey says:

    The myth is “it is possible to construct a working Newton’s cradle using wrecking balls”. They got some wrecking balls and tried to make a Newton’s cradle, as per the viral video and busted it.

    The myth isn’t “can you make a really big Newton’s cradle”.

    Keep in mind these aren’t scientific experiments trying to prove a theorem, they are trying to prove or disprove a myth. If it was the former, it would be any other science program and it wouldn’t be nearly as much fun or as cost effective to produce.

  21. Jack says:

    I chose to leave a 28 year marriage that had brkoen me down to the point of being suicidal. Everything that happened was blamed on me, the bad stuff only, I should clarify. The good stuff never seemed to have anything to do with me, at least I was told this over and over until the reality was so blurred I believed it. I was to blame for my, now ex’s depression. What a surprise it was to me when he went on antidepressants 2 years out. I, the cause of his depression, wasn’t there any more, why was he still depressed? And why didn’t he get help 20 years ago? I wonder to myself why I am writing this, 8 years out and remarried to a wonderful man that treats me like a queen, not even in comparison, just cause he loves me. I think it’s because I hope that some one out there realizes sooner than I did that abuse doesn’t have to be physical to be real’. And to base our self worth on someone else’s opinion of us is doing our psyche a great disservice.

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