4 Revolutionary Riddles

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3 år sedan

Can you solve these four rotation-related riddles?
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I came across these four physics puzzles over the years in discussions with Neil deGrasse Tyson (riddle 4: which part(s) of a moving train are going backwards with respect to the ground?), Simon Pampena (riddle 2: run around a track twice, the first time slowly, the second time much faster so that the average for the two laps is twice the speed of the first lap). Someone tweeted me a video of the mystery cylinder rolling down the ramp in riddle 1 (sorry I'm not sure who it was). Riddle three about a bicycle going forward or backward when it's bottom peddle is pulled back was brought to me by a number of people and I appreciate all of their help!
Filmed by Raquel Nuno.
Thanks to everyone at the Palais de la Decouverte! I've had this footage for five years and am only finally releasing it now. I wanted to talk about the way grass grows on a spinning turntable but I couldn't locate the footage...

Radhika 15 timmar sedan
Bermuda triangle... mystery..????
umberto smerilli
umberto smerilli 4 dagar sedan
1.viscou fluid maybe honey 2.bike goes backward but the rear wheel doesen't turn 3. Speed of light 4.the bottom half part of the wheels are moving backward
sagenhaft sose
sagenhaft sose 4 dagar sedan
Ik im late but hmh 1. I think oblec 2.backwards 3.im not good in math 4.i when i ran like sonic
Kellie Lawson
Kellie Lawson 4 dagar sedan
"the earth is after all just like a big turntable" Oh my Oh my, flat earthers incoming
Alex Lüdeking
Alex Lüdeking 5 dagar sedan
All the seats and their occupants that are facing the back of the train are moving backwards as the train moves forwards.
Oscar Aaccosta
Oscar Aaccosta 6 dagar sedan
1. A 2. C 3. D 4. C
Ayush T
Ayush T 7 dagar sedan
1. As we see, the cylinder has a strip of transparent tape attached to it. So according to me, first the cylinder rotates a little due to torque by friction, but as the strip comes in contact, it must be having a different coefficient of fricn(and i think it is small than rest of the material of cylinder). So basically the frictional force changes everytime the strip come in contact with ground
Bernhard Diener
Bernhard Diener 7 dagar sedan
The bike behaviour depends hardly on the gear translation which is used. Is the gear translation small, then the pedal backwards movement is bigger than the bikes forward movement whith the 90° pedal turn, the bike will go forward a bit. But if the gear is so big, that bike wants to go forward more than the pedal moves towards the back, nothing will happen. It looks like the gear in the front is about double the gear in the back. That means that 90° pedal turn causes a 180° wheel turn which lets the bike go forward one or at least half a meter. But the peddal doesn't go backwards so far. So you cannot move the bike like this.
W-youtube 8 dagar sedan
SAT's be like 💀
P100 9 dagar sedan
I think wheels are moving back divide wheel into 2 parts upper part and down part, down part is always moving back, half of wheel is always moving back
brain eater zombie
brain eater zombie 11 dagar sedan
Honestly i solved que no.3 and 4 in a minute No.3 ans- infinite No.4 ans- the lowest point of the wheel
Jehanzeb Qasim
Jehanzeb Qasim 12 dagar sedan
1.the cylinder has a viscous liquid like honey
Scooty Puff Sr
Scooty Puff Sr 13 dagar sedan
1. Thick fluid. Like molasses for example. 2. Not Move 3. 4 times as quick. 4. 🤔 the only two objects that I could think of are the wheels or pistons inside the engine. But that doesn’t seem right since engines can vary and you’re saying EVERY train. They usually have multiple locomotives. Typically 1 is in reverse in respect to the train but that can’t be the answer. So I’m a little stumped.
Nitin Singh
Nitin Singh 14 dagar sedan
1.Honey 2.Infinite speed 3.Will go backward if you pull it tighly else wise it will not move. 4.No parts (the bottom of train wheels travel at 0 speed with respect to ground but not negative)
Dmitry Kozlovtsev
Dmitry Kozlovtsev 16 dagar sedan
1. Probably some gyro mechanism 2. it will move forward like normal pedal pushing, until pedal turn completely to the right 3. you should run the same speed as first lap 4. every wheel turn backwards with respect to the ground
rajsekhar mahapatro
rajsekhar mahapatro 17 dagar sedan
4. The point of contact of the wheel with the track moves backwards when the train moves forward
Anasانس Al-Fahidiالفهيدي
Anasانس Al-Fahidiالفهيدي 17 dagar sedan
the gear change reverse the power man . like gyrscope .
Tony James
Tony James 18 dagar sedan
For those just seeing this video now, here are the solutions - svfrom.info/history/video/Z5V9d6KXqN-tf5U
Physics for Lisa
Physics for Lisa 19 dagar sedan
For number four, it is not the wheels. The bottom half of the wheels is in contact with the rail at the bottom. Assuming that the wheels arent sliding(train burnouts arent a thing) they have 0 speed relative to the ground. However there are probably a dozen or so reciprocating components in the trains external combustion engine that are moving backwards(and forwards) relative to the ground but I dont think thats the answer hes looking for either
Art Avian
Art Avian 19 dagar sedan
1) A very viscous liquid 2) probably shouldn't move 3) Thrice of V1 4) The smoke, The Tracks are going backwards
Diptanjan Sinha
Diptanjan Sinha 21 dag sedan
1. No idea 2. Go forward 3. I guess 3*V1 4. Light or sound coming from the train
Kazumi 22 dagar sedan
4 are the Traintracks
The RealButcher (Peter from Holland)
The RealButcher (Peter from Holland) 22 dagar sedan
He said.."backwards, compared to the ground" .. so, not the wheels. But, look at the shape of the lower part of a train wheel. Get it? Goes backwards, compared to the ground.
10_D_Prince Kumar
10_D_Prince Kumar 23 dagar sedan
1. Water 2. Backwards 3. 3v1 4. ENGINE
Zethorer - What does that mean?
Zethorer - What does that mean? 24 dagar sedan
1 : magnetic ranp and that box contains magnets at some parts 2: backwards 3 : infinite 4 : bottom most part of the tires
Ridvan Vejzagić
Ridvan Vejzagić 24 dagar sedan
If the bike is gonna go forward really depends on the gearing ratio tho
Cameron Widhalm
Cameron Widhalm 24 dagar sedan
1. The cylinder has a diaphragm and water in it and there’s small holes in it that allow water through so it can turn, but the holes are small enough that it stops so the water can flow 2. The bike would go forward (initially) then fall, since the pedals push at a different ratio than the wheels (because of the gears) the pull from the pedal would propel the bike initially. 3. 3 times the speed (arbitrary calc. V1 = 10 mph, V2 = 30 mph, Vave.= 40/2 =20 and 20 is 2 x 10 4. I really wanted to say the bottom of the wheel but that’s only if the wheels slide. I also wanted to say the force pushing the train but that’s not “part” of the train. so I’ll guess the part of the fly wheel of the engine that is spinning in the same plan as the wheels (one side moves backwards and one side moves forwards)
Julius Reyes
Julius Reyes 25 dagar sedan
b**'))) s s f P•
Dubstrom Official
Dubstrom Official 25 dagar sedan
B D 25 dagar sedan
There's tape so it sticks and then gravity pulls it down and it repeats
Diago Le Ben
Diago Le Ben 25 dagar sedan
Flat earthers theory confirmed: "the earth is after all one giant TURNTABLE.."
TrustedJoy 25 dagar sedan
1. It is magic 2. The bicycle is faulty so ut will break 3. 3 times velocity 1 [[Full equation == X = velocity in lap one Y = velocity in lap 2 (x+y)/2 = 2*x x+y = 2*x*2 x+y = 4*x y = 4*x-x y = 3*x y = 3x]] 4. The wheels on the train go back-backwards
GURA VIRUS 25 dagar sedan
weird algorithm
Tashy Jamal
Tashy Jamal 25 dagar sedan
the horses name was friday. Hope this helps
Tommy Nguyen
Tommy Nguyen 26 dagar sedan
this a late comment and I'm pretty sure u have the video already but solution 1 is a container filled half with honey and an iron ball...since the iron ball is stuck in the honey it wont roll; very well since the center of mass is at one place it wont roll that much unless over a 45 degree angle slope. So unlike a regular water bottle rolling fast the capsule rolled very slowly. if u want to see the rolling smoothly i prefer using a capsule ball...fill half with honey place the iron ball in the middle close it and tape up the holes. Psst nice videos...really high quality and all.
Nintendoom64 26 dagar sedan
Lol. Literally everyone saying you gotta go three times as fast like a riddle would be that easy. The answer is infinitely fast, and no, I'm not joking. The answer would be three times as fast if instead of saying "you ran a mile twice" you said "you ran for an hour twice". Say you went a mile lap in 1 hour. You went one mile per hour. In order to make your average speed 2v1 it would have to be 2 miles per hour, and 2 miles is the length of 2 laps... But wait, you already used up your hour. So you would have to instantly complete the second lap. If you ran 1 mile in an hour (1mph) then ran 3 miles in an hour (3mph) you went 4 miles in two hours or 2mph or 2v1. But that is 4 laps... Not 2 like the riddle says. Edit: this is just like his video about measuring the speed of light.
OMGit‘s OwenJ
OMGit‘s OwenJ 26 dagar sedan
1:Water in a little bottle 2:The bike's not going anywhere because the man's holding it. 3:1st lap is V1 then the second lap is 3V1. Add them together and divide by 2 to get the average (mean) is 2V1. 4:The bottom of the wheels on the train are moving back respective to the ground or the track as circular objects, like wheels, when they move will alwase be able to move from a 270° angle at the centre of a wheel to the 90° angle, therefore alwase moving forward and back.
Rahul Gupta
Rahul Gupta 27 dagar sedan
1 there is problem with center of gravity, it's not on the axis of cylinder.. 2. If u pull back, might be it will move in circular track.. 3 3 times of v1.. 4 wheel of the train...
Cooke Tarlton
Cooke Tarlton 27 dagar sedan
Ryan Stricklin
Ryan Stricklin 27 dagar sedan
1. An extremely viscous liquid 2. Remain stationary ( pedal moves not the wheel) 3. 3 times faster than v1 2(avgV) = (V1+V2) /2(2) or 1(V1)+3(V1)/2 = 2(V1) 4. Sound
Felix Fourcolor
Felix Fourcolor 28 dagar sedan
Number 3 is not 3 times. It's infinitely fast.
Levi Ackermann Senpai Notice Me
Levi Ackermann Senpai Notice Me 28 dagar sedan
There is water in the mystery cylinder. I am sure of it.
Joris Degen
Joris Degen 28 dagar sedan
0:33 _happy flat earther noises_
Scott G
Scott G 29 dagar sedan
1. Sand 2. Will not move if tire friction is not lost. 3. V1 = 2mph & V2 = 6mph 4. I don't know...maybe one of the joints on the wheel arm?
Ravindra Singh
Ravindra Singh 29 dagar sedan
Frank Hughes
Frank Hughes 29 dagar sedan
1. thors hammer (small) 2. lego 3. faster than i can ever run 4. idk now lets go see how correct i was...
Shihab Mohammed
Shihab Mohammed Månad sedan
1. Mercury in the Cylinder 2. Cycle go Forward 3. X2 speed of V1 4. Center part of the train go backwards
Steffen W.
Steffen W. Månad sedan
1. half honey, half air 2. backwards 3. infinite speed: 1round/v+1round/oo=2rounds/2v 4. (surrounding) air
apex destroyer
apex destroyer Månad sedan
tape paris london russia
moris preciosa
moris preciosa Månad sedan
1. Theres a hamster in the cylinder
Doug Dimmedome
Doug Dimmedome Månad sedan
3. Vavg = (V2 + V1)/2 Vavg = 2V1 = (V2 + V1)/2 4V1 = V2 + V1 V2 = 3V1 3 times faster
benbuzz790 Månad sedan
3 years late... 1. Some kind of fluid hourglass shape 2. The bike will move forward about two inches 3. 3V1 4. The bottom point of the wheels are stationary wrt the ground, but there is a gear train somewhere with a gear spinning faster than the wheels. The bottom of that gear moves backward wrt the ground.
benbuzz790 20 dagar sedan
@Tahzib Mashrik That's true, but it's stationary relative to the ground. Turns out I got a lot of answers wrong, haha.
Tahzib Mashrik
Tahzib Mashrik 27 dagar sedan
The part of the wheel that is in contact with the ground is moving in the opposite direction to that of the train.
Aarush Sehgal
Aarush Sehgal Månad sedan
Honey in cylinder
Beacon Blaster
Beacon Blaster Månad sedan
1. something with sides 2. backward, if pedaling forward on a bike the bottom pedal would travel forward because of differential 3. no! 2v1 is achieving 2 laps at the same time 4. the train. the train is moving backward
Kara Rawson
Kara Rawson Månad sedan
thank you :)
Emon Slizky
Emon Slizky Månad sedan
1. water 2. forward 3. V2=3*V1 4. sides of spinning wheels
Morris-Jeremy Wachira Wanjohi
Morris-Jeremy Wachira Wanjohi Månad sedan
How are people getting 3 when my answer is Jupiter?
rebelwave100 Månad sedan
0:02 I'm sorry im going to have to pause here did you say "Palace of Discovery?" .... I'll be back
David Robinson
David Robinson Månad sedan
4) On the equator left to right or vice versa, 1) Magnets involved
Benjie's Status
Benjie's Status Månad sedan
1. Water 2. Forward 3. Thrice the ospeed for the first run 4.The Smoke(for diesel and coal engine trains)
Da Parrot
Da Parrot Månad sedan
the answer of 4 is "The wheels"
GT calvii
GT calvii Månad sedan
so ur not gonna put the answers in the video? fail
anjanlee Månad sedan
2:43 should be 3x faster then V1
TheXenoXae Månad sedan
1 a pendulum 2 backward 3 v1+v2/2 4 the train itself
DIY Films
DIY Films Månad sedan
1. An unbalanced center 3. 3×V1
Good Old Doug
Good Old Doug Månad sedan
Dudeska Månad sedan
1. Another Cylinder inside it?
therealthomas jefferson
therealthomas jefferson Månad sedan
1 the cylinder has a counterweight 2 the bike will go forward until the peddle is in the back and it will stop unless it falls over first 3 for your total speed to be twice v1 you would need to go infinitly fast 4 the axle will travel backwards relative to the ground
shiranth Shiranth.b.s
shiranth Shiranth.b.s Månad sedan
Another small cylider inside that
Sameer Sawant
Sameer Sawant Månad sedan
Borut Bergant
Borut Bergant Månad sedan
1. liquid with high viscosity 2. backwards 3. 3xV1 4. The wheels
Watson Harrell
Watson Harrell Månad sedan
Jesus loves you brochachosy
Samuelprince Nimley
Samuelprince Nimley Månad sedan
1. The liquid particles in the container are having elastic collisions with the container walls. Meaning the liquid is hitting one side of the container then hitting the other side. The force of theses hits are making the container go backwards. 2. It would move. Because the gear moving clockwise is what pushes the bike. The bike doesn't care about how it is moving clockwise. 3. V average = 2 (V one) 2 (V one) = V one + V one V average = V one + V one V average = V one + V two V one + V one = V one + V two (V one = V two) is the only way the equations above would make sense. Meaning you would have to run at the same speed for both laps. 4. Maybe the sound of the train is going backwards.
Samuelprince Nimley
Samuelprince Nimley Månad sedan
@Jenna Tolls And why must you be so mean about it.
Samuelprince Nimley
Samuelprince Nimley Månad sedan
@Jenna Tolls I see my mistake now.
Samuelprince Nimley
Samuelprince Nimley Månad sedan
@Jenna Tolls Oops
Kevin Mcmaster
Kevin Mcmaster Månad sedan
00:33 - did Veritasium just go full flat earth?
Sadabahar Gaane
Sadabahar Gaane Månad sedan
4) circumference of wheel
Adam Ghatta
Adam Ghatta Månad sedan
number 3 is not a riddle just simple math
Maybe Matt Martin
Maybe Matt Martin Månad sedan
1. Theres a string thats circling 2. Forward 3. 1 4. The thing thats like a line
Rqmxzz Månad sedan
YUG PATEL Månad sedan
Andrew Werstler
Andrew Werstler Månad sedan
Imagine being so desperate for views so u make a 5 min vid in to 2 separate 10 min vids
Raulson Fontana
Raulson Fontana Månad sedan
What do people can try to answer the riddles, chill out man
BlackQuest Månad sedan
1. T H I C C liquid 2. Not anything 3. Very fast 4.Steam (if it’s a steam engine train or a cup of coffee)
Press Start
Press Start Månad sedan
1) The bike will resist you and will likely not move. 2)3 V1 3)the wheels at the point of contact with the rail.
Ping Pong Cup Shots
Ping Pong Cup Shots Månad sedan
The point of contact of the wheel to the rail doesn’t move backwards
Lucy Kitsune
Lucy Kitsune Månad sedan
1 - Pendulum 2 - Forward 3 - The second lap has to be finished instantly or be infinitely long, so v2 has to be infinite 4 - The bottom half of all the wheels
Ben Frish
Ben Frish 25 dagar sedan
@Lucy Kitsune Ohh so it's just v1/2, I thought he was asking v1+v2/2. In that case you're right it has to be instant
Lucy Kitsune
Lucy Kitsune Månad sedan
@Ben Frish No, because the average velocity is the distance traveled divided by the time spent, so to get an average velocity of v1/2, you'd have to spend zero time on the second lap
Ben Frish
Ben Frish Månad sedan
If you go 1km/hr for v1 and 3km/hr for v2, the average is (3+1)/2 = 2 mph so it had to be 3 times as fast as v1
Mitchell Hermann
Mitchell Hermann Månad sedan
Idk the first 3 but my guess to number 4 is the top of its wheels, when the wheels are spinning the top is going backwards. Not sure tho I’m not very smart lmao
TheUglyBanana Månad sedan
1. water 2. stay 3. 3V~1 4. wheels
B3rnard Månad sedan
First lap 3 minutes second lap in 1
Potato Tato
Potato Tato Månad sedan
I'm not seeing many people saying that the bike would move forward. Wouldn't it move forward? I'm not a physics expert so correct me where I'm wrong, but the distance that the wheel spins is greater than the distance you move the pedal. So if you turn the pedal a little, the bike will move forward more than the distance you pull backwards (mechanical advantage greater than 1 meaning distance increases inversely proportionally to force). Wouldn't this mean that the bike would move forward from where the pedal is at the bottom until the pedal is at the back? After that, pulling backwards wouldn't make the wheel turn, so then it would go backwards. Help
Black Enderman
Black Enderman Månad sedan
4. The rails
Sufiyan Bilimoria
Sufiyan Bilimoria Månad sedan
1 water in the cylinder 2 the front wheel will stay down and the back wheel will go up 3. 3 times as fast 4. The trains wheels
PyjamaMC Månad sedan
Idk the fourth one is probably the steam. I know that the 3rd one isn't 3 cause reasons and it's probably a fair bit greater than 3, and I think I saw a similar experiment of the first on with honey inside of it. I saw someone explain the answer in the comments so thanks a lot you ruined it for me. Anyways going to watch the second video, promise I won't edit this comment to make me look big brained.
Arno Nym
Arno Nym Månad sedan
v2 = 3*v1
Youtube official
Youtube official Månad sedan
4 =Wheels✓
Fatimah Sabir
Fatimah Sabir Månad sedan
wwo vapoer makes my man section hard like stonwe rock
Thanya Beck
Thanya Beck Månad sedan
1. Weight’s? 2. Stationary 3. Depends on your speed 4. Wheels
Sam Leen
Sam Leen Månad sedan
Well I guess a metal ball counts as a weight
Ammar Ali
Ammar Ali Månad sedan
Q4: Steam🙃
no name
no name Månad sedan
2、假设第一圈速度为v,第二圈为u。一圈长度为S。平均速度为2v。则S/(S/v+S/u) =2v。上下同乘以uv除以S。最后推导出2v+u=0。因u、v同为自然数。所以无解。或者两者同为0,同样无意义无解
The smoke goes backwards xD
Riley Geidel
Riley Geidel Månad sedan
Joseph Simunek
Joseph Simunek Månad sedan
Am I wrong that his intro sounds very 2004 science show
Zach Thomas
Zach Thomas Månad sedan
1. No idea. Probably something that can move around like water or an object. 2. Pedal will be pulled backwards, wheels will go forward, until the pedal completely reaches the left side and you start dragging the bike backwards. 3. You can't, for the average speed to be double, you should have already been done the second lap by the time you finished the first. (how is this related to rotation though...?) 4. The bottom of the wheels in theory would be stationary relative to the rails (and therefore ground), but due to friction not being 100%, they slide backwards relative to the ground.
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