I am over at Goldsmiths College later today to give a research talk on parapsychology – details here – do come on over if you are around!
I am sure that many of you will have seen this great take on the old tablecloth science trick…
My question is……is it fake or genuine and why?
Oh, and if you missed it, here is my video containing 10 science stunts for parties (including the tablecloth trick)
It looks like there is a thin sheet of something like Perspex under the cutlery. It’s just so smooth. I can’t really call it either way but my gut feeling is that it MUST be fake.
I call fake. None of those knives or forks moved at all.
Fake.
The tablecloth would not be taut enough at the end furthest from the motorcycle to have the immediate speed required to keep the settings from wobbling and toppling over.
Most certainly fake – watch it in frame by frame, distinct camera movement and frame jump from bike taking up slack and table cloth missing – well done though I thought.
Definitely fake. It’s too slow to work.
Oh I feel silly now, frame jump was caused by me – LOL.
I still call it fake, assisted fake maybe. First poster suggested perspex and I agree. I think the table set is on top of the perspex, the table cloth underneath it. As the bike rider rides away the perspex is being held back by a sling set up at the opposite end.
If it is real – Well Done!
Definitely fake. a) your video specifies pulling downwards and b) using heavy objects
I’ll assume you didn’t just throw those in for the fun of it and say the fact they have small, lightweight cutlery is not the kind of setup one would use in such a trick and expect that result.
Now, I’m no expert, however the thing that really cements this as faked I the fact they’re using such a massive tablecloth meaning force would be applied over a far greater period of time for a lot of the tableware, almost certainly making them move more than they did. Also the way it was fastened means that the ends would be pulled together, which would cause the ends to bunch inwards above the table (the hooks are above the cloth level, you see this in the video) which would almost certainly result in the cutlery being moved or at least the things closer being more destabilized than the things further away.
Now, you have a fixed camera that could have had artificial wobble applied allowing them to superimpose the dinnerware above a shot of a cloth being pulled off an “empty” table. All you have to do is record that dinnerware being shaken slightly for effect and voila.
Or you could just use a bunch of magnets under the table. You know, if you can’t be bothered with simple green screen effects
I know this is just about inertia, but I have the feeling that if I put the numbers in the calculator the cloth would rip, all those sliding coefficients must add up.
The perspex/glass is pretty obvious to see. Doesn’t mean it’s not possible to do it for real (in theory!) – probably saved a bit on the props department budget by doing it like this though!
Fake! The stuff on the far right may stay in place but for the stuff on the far left, there will be friction with the table cloth for a much longer time. The objects’ inertia won’t be enough to keep them at place; with friction cloth will transfer more speed to the objects in time, thus by the cloth is totally pulled under the object, they will have quite a bit velocity.
Agreed. I was going to post basically the same reasoning.
The trick works because inertia overpowers friction in the brief time it takes for the “normal” version of the trick to work. The relatively large amount of time it takes for the “XXXL” version means friction would have plenty of time to overcome the inertia.
It’s true ! Really true !
It’s simple : you just have to take forks and knives of ten thousands kg each.
How about assisted? Teflon coat on both the cloth and contact surfaces of tableware, maybe.
Watch the bad acting after the stunt. If something like this is successfully done you would expect the ‘crowd’ to be more genuinely enthusiastic?
Totally fake. There’s no way a motorcycle (or any vehicle) can accelerate quick enough. Speed and Power is irrelevant, it’s all in the initial yank. I believe the technical term is “Jerk”, which is actually the rate of change of acceleration.
Agree. You don’t even have to watch beyond seeing the table, there’s just no way you get enough acceleration. The cloth has to come completely off far faster than you could ever get up to that way. Now there could be something between the tableware and the cloth to make it work, so it need not be CGI, but they’re not doing the trick honestly.
I think they tip their hand at it being rigged in some way simply by not showing it twice. Why did they show the driver revving the engine and yelling at the end of the clip instead of …oh i don’t know…. a slow motion replay of this amazing feat you just allegedly performed?
I’ll say genuine, because everyone else says fake. However, the physics seems wrong, so the props aren’t quite as they appear. I *think* the jerk can be managed if the length of the rope between the bike is elastic or long enough only to be taut when the bike is at the correct speed, so there’s a very much quicker acceleration from rest to 60 mph or whatever.
Fake ; one solution would be to cut slits in the table cloth to allow the objects stay in the same place.
The video is edited just after the stunt, maybe with a normal table cloth hanging behind the bike.
Well done though !!
I’m leaning towards fake. When you remove the table cloth in the classic trick you always get some movement and that movement is greatest near the point from which the table cloth is moved. This movement is proportional to the coefficient of friction for the item and the amount of time the item spends under the moving tablecloth. The tablecloth took an appreciable amount of time to remove (over a second). Given that at the very least the tablecloth would have had to have an extremely low coefficient of friction so low that it wouldn’t be cloth in any of the usual meanings of that word.
Additionally it is likely that some of the glasses would have received a static charge.
I’d love to see the outtakes!!
Sorry I have no opinion either way, I just had to say that this trick makes me think of the ballroom scene in Ghostbusters every. single. time!
Fake – i also spotted the perspex or whatever it is.
Still very cool to watch
I don’t see any glass, and taking the time to do it frame by frame sounds silly to me, it would take a greater effort than this.
I think the variables are friction and speed, the objects need not to be heavy, rather smooth, which is the case of plates and silverware. (sorry if I am miss speling something)
and of course it is about inertia, the stuff on the table tries to stay put, the forces of gravity are greater than those of friction, so it rather stay on the table than join the table cloth…
of course I am not doing the math, but that is what I think… awesome clip!
The acceleration of the bike is certainly sufficient for the effect. It’s easily enough to leave its rider behind from a standstill, let jerk at a stationary object after it’s had a meter to accelerate. I’m withholding judgment for the time, though.
Looking at the objects after the effect, they do seem to have moved as you’d expect if it were genuine. The silver is skewed with its least massive end moved in the direction of motion, and there’s a subtle motion at the very beginning of the tug. After that, it’s a little troubling that things seem all too still, especially the top-heavy candelabras, but given the right conditions, it seems moderately plausible.
I know that if I were doing the trick, I’d have done everything possible to make it genuine before resorting to tricks, and as I think the effect is plausible, I’m going to give them the benefit of the doubt.
I tend to agree that it’s fake. The biggest point for me is the fact that the items nearest the bike don’t move more than those farthest from the bike.
For what it’s worth, if you wanted to do this for real, I’d say use a longer cord between the bike and the tablecloth, and give it some slack initially. That way, when the bike jerks the cloth, it’s already going at a good speed.
Cool idea, though. And a good video.
I think it’s fake- but it looks brilliant. I’m going to show my husband, he’ll love it to because (according to him) his bike can go at 450mph!!!
Aaww…I thought it was genuine and they looked genuinely pleased. Gullible?
Fake. Good idea though, but should have had some movement to add more realism.
Definitely fake.
1. The real trick involves pulling downwards not horizontally.
2. The cloth would bunch and rip.
3. Only 1 fork or candlestick would have to catch on the cloth for a split second to bring all the rest flying down the table.
4. The visible perspex.
5. Mr Andy Nyman said it was a fake and he knows a thing or two about illusions.
6. The fake spectator reaction.
7. The forces acting on the cloth would be unpredictable and haywire beyond the first two feet of table, causing the above-mentioned bunching and ripping, particularly in line with the two attachment points for the cord.
Otherwise, a bloody good job and an entertaining illusion.
Over at the Mythbusters forum http://community.discovery.com/eve/forums/a/tpc/f/5261919888/m/39619146401 they have it pegged as fake.
Fake. Aside from anything else, different objects have different weights and vibration alone would unbalance some items. Also – with all that weight on it, the cloth would tear!!
By the way, a suggestion about your own video. For some people (like me and, probably a lot of other ‘oldies’) having background music and your voice at the same time, makes it difficult to understand. Our brains don’t process as quickly as young ‘uns. Of course, if your blog is just for young ‘uns, then that’s fine… Personally, though, I had to give up well before the end of the vid, which seems a shame.
acceleration too slow to begin with…
It is obviously fake.
It was also a nice chance to bring to mind some basic physics.
The tablecloth will exert a lateral force against every object on it during the time the tablecloth moves underneath. This force will be proportional to its mass and the coefficient of kinetic friction, F= u * m * g
u: coeff. of kinetic friction
m: mass
g: acceleration due to gravity, 9,8 m/s²
By Newton’s second law we find that each object will be in a uniform acceleration motion, being its acceleration a= F / m ; if we use the first equation we find the mass cancels, so a = u * g.
As long as the tablecloth passes underneath, every object will move sideways in a uniform acceleration motion, its acceleration depending on the coefficient of kinetic friction only, regardless its mass.
If the initial speed is zero, the distance travelled in such a movement is:
x = (1/2) * a * t² (in general)
x = (1/2) * u * g * t² (in our case)
My estimation is that the time that it takes for the tablecloth to pass the length of the table completely is around 0.8 seconds. Supposing a coeff. of friction of 0.04 (which is extremely low, let’s imagine a perfectly flat Teflon coated cloth against well polished steel) the result would be 0.125 m, or 12.5 cm. It is obvious that the objects don’t move as much if they move at all.
Physics are fun!
I was wondering if the bike could accelerate fast enough so it could remove the tablecloth from the table in less than a second.
There is a limit in the acceleration a bike can achieve, supposing it has enough horsepower and the grip against the ground is good and does not slip. This limit occurs when the acceleration is so great than the front tire starts to lift off the ground. A little more acceleration and the bike would make a “wheelie”.
I got a side photograph of the BMW bike and drawn the forces acting upon it at maximum acceleration. You can see it here:
http://s873.photobucket.com/albums/ab299/jhualde/?action=view¤t=bmw-sbk-1-400x234_cr.jpg
As the vertical acceleration is zero, the sum of the vertical forces is zero too, so the vertical force on the rear wheel R is equal to the weight of the bike plus rider, or mass times g.
Thrust force F is what makes the bike accelerate forward. As we are considering a rectilinear continuously accelerated motion, we can assume the sum of momentum around the centre of mass will be zero:
mgx=Fy
From this we have that F=mgx/y
As F=ma, we want to calculate the acceleration a=F/m=(mgx/y)/m.
Mass m cancels, so we have that the maximum acceleration is:
a=gx/y
I estimated x=0.820 m and y=0.525 m, so a=9.8 m/s² * 0.82/0.525 = 15.3 m/s²
That’s pretty impressive. If the bike could keep this acceleration, it would reach 100 km/h in less than 2 secs.
My estimation of the length of the table from the video is d=7.5 meters. The time it gets to cover this distance at the constant given acceleration is:
t=sqr(2d/a)=0.99 seconds
My gess from the video was more like 0.8 sec. If we assume that the time is 0.99 instead, the movement of the items (in the “bike” side of the table, the farther from this side the less the movement would be) would be 19 cm.
Real or Fake? It’s ADVERTISING. ‘Nuff said
Then it must be real, because as we all know, advertisers aren’t allowed to fake things or make stuff up.
For me the biggest give away is not that it is a lateral pull(almost but not quite), but it is still slightly upwards, you see the sheet bend up when tension is first put on the cloth. The sheet is tied to the bike at a point higher than the surface level. If you ever try the normal trick, and pull slightly upwards it really messes with the physics, making it all but impossible, that is why pulling downwards will keep it a pure lateral motion.
I called this out as fake a couple of days ago on my blog over at http://www.nathanrae.co.uk/blog
But I meant that the video was a fake “user generated” video. These were paid (bad) actors pretending to do a stunt for the love of it. Oh well.
I’m thinking of getting out my motor bike and doing this for real though. Any one in Manchester want to help recreate it to see what really happens?
Nathan
it is possible since the speed of the motorcycle seems sufficient enough to do the trick but, i wasn’t there so i wouldn’t really know…but great trick by the way really cool stuff…
Is it just me, or is there something odd about the way the candlesticks wobble as the cloth comes free? They stabilize far too quickly.
I wonder whether it will work for real if we let the bike reaches say 100km/h before the rope/tablecloth catches on?
The Dot Physics blog by Rhet Allain of at scienceblogs.com does a pretty good job of analyzing the actual physics behind this exact stunt. Very interesting.
http://scienceblogs.com/dotphysics/2010/03/tablecloth_and_dishes_trick_-.php
[...] Genuine or fake? I am over at Goldsmiths College later today to give a research talk on parapsychology – details here – do [...] [...]
It doesn’t look quite right, and I’m inclined to think it’s fake – however, in the initial version with the guy pulling I estimate the cloth moving about 3m/s, and in the bike version _at the point at which the cloth becomes taught_ the bike appears to be moving about 4.5m/s. – by the end of the pull the bike is moving about 25m/s so it seems possible.
Fake as Hell (literally).
I thought there would have been a long rope so it pulled when the bike was going fast.
This was just ridiculous.
fake purely because the acting was so bad.
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[...] Genuine or fake? « Richard Wiseman's Blog [...]
fake! it have to be pulled downwards to be a sucsess. but it’s very good made..
I will try all this trick. Very good.
I have no idea what Persplex even is, but it still looks fake. The tablecloth sliding just looks un-natural.
Fake. At 42 seconds you can see how the tablecloth retains it shape better than it would normally. Also, the second video demonstrates, you have to pull downward to make the trick word. And, finally, a mistake of their own making. This video obviously had some thought put into it. And They obviously had more than one camera. Why, then, during the actual pulling off, do they have such a low angle that we can’t see the top of the table? It can only be because:
IT’S A FAKE!!
definitely fake !!!
first of all, the video advertises bmw
and the visible acceleration is not enough for this thing to work.
Totally fake. That trick just work if you do it vertically, and the motorbike does it horizontally…
Tablecloth trick! One of the oldest trick ever!
i say it’s plausible. it’s hard to believe the bike has enough acceleration, but it doesn’t have to. notice there’s considerable slack in the rope before the bike accelerates. that means when the bike begins tugging on the tablecloth, its initial velocity is significant.
very happy to read your blog.Thank you for sharing this article.It is great!
Thanks for sharing this nice post.I will keep your article in my idea.
[...] = 'wpp-262'; var addthis_config = {"data_track_clickback":true,"ui_language":"es"};Lo veo en el blog de Richard Wisemann. Pregunta el psicólogo si el vídeo es un fake. Queda abierta la [...]