# How does a man move a train with his teeth?

Recently, I came across this website. John Massis here pulled 15 tons, about 13607.8kg of heavy train for 15 meters using his teeth, biting onto a rope that connected him and the train. Even a weight-lifter cannot carry something so heavy. How was this even possible? I would think Newton's second law might apply here, but I am still unsure how he managed to accomplish such a feat. In addition, he also managed to prevent helicopters and motorcycles from taking off! How is that possible?

• would appreciate if downvoter explained – QuIcKmAtHs Jan 7 '18 at 1:37
• Possible duplicate of The best way in which a man can pull a train – sammy gerbil Jan 8 '18 at 16:21
• I am merely asking how a man can use his teeth to pull a train. What do you mean “what are the conditions”? I told you the weight of the train, so now I want to know how he accomplished such a feat. – QuIcKmAtHs Jan 8 '18 at 21:47
• I apologise, I am being too critical. I will withdraw my down-vote. – sammy gerbil Jan 9 '18 at 14:12

The article you cite does not give the size of the force which John Massis was pulling against. He was not lifting the train, plane, helicopter or motorbike, so the weight of those objects is not a reliable measure of his strength. In many cases the force required is surprisingly low. The record for a single lift with the teeth is about 280 kgf (Massis' record in 1977 was 233 kgf), while for repeated lifts or a constant pull over distance 100 kgf is more usual. This gives you an idea of the force actually used to pull a train.

Newton's 2nd Law tells you that even a small amount of net force will cause a very heavy object to accelerate. There is no mention of the acceleration here, so we cannot use it to estimate the minimum force used.

How much force can be transmitted through the teeth depends primarily on how firmly they are fixed in the skull. Experimental Study on Strength Evaluation Applied for Teeth Extraction: An In Vivo Study shows that each tooth requires about 15 kgf for extraction (146 Nmm average gripping value, with 9.8 Nmm equivalent to 1kgf) so a minimum of 18 teeth would be required for a load of 280 kgf. Biting on a rope is unlikely to engage enough teeth : it would be more sensible to bite on a wooden plate, as done in the last photo of your article. The teeth extracted in the study were likely to be diseased; healthy teeth can sustain greater force. There are 32 teeth in an adult skull, so the maximum force which they could provide is around 500 kgf.

A secondary limitation is how strongly the jaw is attached to the skull. A Scientific American article on The Power of the Human Jaw states that the bite force can exceed 275 lb (125 kgf). The force provided by the jaw mucles is 4 times closer to the pivot, so it can exceed 500 kgf.

The force with which a motorbike can pull is limited to the friction force (traction) $\mu W$ between the tyre and ground, where $W$ is the combined weight of the bike and rider, and $\mu$ is the coefficient of friction. $W$ is typically around 250 kgf while for sand in a circus ring $\mu$ is about 0.6. So John Massis was pulling with a force of about 150 kgf, which is the weight of two average adults. Impressive but not superhuman.

Note that the traction of the motorbike can be reduced by pulling upwards, as seen in the photo in your link and in this video at time 2:08. This reduces the normal reaction, hence the friction on the tyre. As shown by Friction to just move the blocks a smaller force of $\frac{\mu}{\sqrt{1+\mu^2}}mg$ is sufficient to stop the bike. This reduces the required pulling force from 150 to 130 kgf.

As Akhmeteli shows, the rolling resistance to be overcome to get a 13.6 tonne railway carriage moving is only 70 kgf, which is easily achievable. For a railway engine the force could have been around 2000 kgf, which would easily dislocate the average human jaw. Despite their heavier weight, the coefficient of rolling resistance (CORR) for railway vehicles is much smaller than road vehicles, which explains why they are preferred. (It is also much easier to push against sleepers than try to gain traction on a road.)

In this video a carriage (not engine) is pulled using the suction from a rice bowl, as mentioned in Physics behind seemingly-impossible "rice bowl suction" Guinness world record? In 2007 Indonesian Raja Gigi ("tooth king") pulled a 300 tonne train with his teeth. Again this consisted of modern coaches, not engines.

For the airplane stunt note that the strongman is pulling against the static thrust of the engine. This is significantly less than when the plane is moving through the air, for which the engine is optimised. The static thrust of propellers is typically 50% of the theoretical limit, compared with 80-90% when in flight.

In this case rolling resistance and ground friction act in favour of the strongman, not against him, so it is easier to hold back a heavier aircraft than a lighter one. Likewise, the weight of the helicopter assists the strongman.

The specification in your article (36 tonnes, 200 hp) is probably erroneous. A cargo aircraft of that capacity would have had a hp of around 1500. The photograph shows the tailplane of something much more modest, such as the Focke Wulf S-2 of the early 1930s, which had a max. takeoff weight of 820 kgf, a 100 hp engine, and a top speed of 135 kph. From these figures I estimate a static thrust of only about 115 kgf. The CORR for a soft turf runway is about 0.08, so the rolling resistance could have been up to 65 kgf. A force of only 50 kgf might have been sufficient to prevent take-off.

A heavier aircraft of that era was the ATL-98 Carvair cargo plane, operational from the late 1940s. This had a maximum takeoff weight of 33.5 tonnes, a 1450 hp (1080 kW) engine, and a maximum air-speed of 400 kph (111 m/s). Using these figures I estimate a static thrust of about 550 kgf, a force which a human jaw could just about sustain. Assuming a CORR of 0.01 for a highly inflated tyre on asphalt runway, the rolling resistance would have been about 330 kgf, so the net force required from the strongman would have been about 220 kgf.

Even a tiny coefficient of rolling friction (google that) makes it a mighty tough task. But in the limit, if it's zero, even a small force would get the train moving -- eventually, i.e., just with a miniscule acceleration. So they've apparently polished and oiled the tracks and wheels to the point where the coefficient's small enough so it's humanly possible. You could plug in a few numbers, but I don't see how that would really be very helpful (except maybe to the guy's dentist:)

The formula for resistance of a train on starting is $R_6 = 0.15 W_1 + 0.005 W_2$, where $W_1$ is the weight of the locomotive in tonnes, $W_2$ is the weight of the vehicles in tonnes (http://www.brainkart.com/article/Train-Resistance-Due-to-Starting-and-Accelerating_4339/). In our case, there is no locomotive, so resistance is $0.005\cdot 13.6\approx 0.07$ tonnes.

70 kilogram-force is a lot, no doubt, but not quite sci-fi. So low rolling friction is what can make it possible.

## protected by Qmechanic♦Jan 11 '18 at 14:04

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