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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...

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

Ik im late but hmh 1. I think oblec 2.backwards 3.im not good in math 4.i when i ran like sonic

"the earth is after all just like a big turntable" Oh my Oh my, flat earthers incoming

All the seats and their occupants that are facing the back of the train are moving backwards as the train moves forwards.

1. A 2. C 3. D 4. C

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

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.

SAT's be like 💀

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

Honestly i solved que no.3 and 4 in a minute No.3 ans- infinite No.4 ans- the lowest point of the wheel

1.the cylinder has a viscous liquid like honey

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.

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)

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

4. The point of contact of the wheel with the track moves backwards when the train moves forward

the gear change reverse the power man . like gyrscope .

For those just seeing this video now, here are the solutions - svfrom.info/history/video/Z5V9d6KXqN-tf5U

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

1) A very viscous liquid 2) probably shouldn't move 3) Thrice of V1 4) The smoke, The Tracks are going backwards

1. No idea 2. Go forward 3. I guess 3*V1 4. Light or sound coming from the train

4 are the Traintracks

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.

1. Water 2. Backwards 3. 3v1 4. ENGINE

1 : magnetic ranp and that box contains magnets at some parts 2: backwards 3 : infinite 4 : bottom most part of the tires

If the bike is gonna go forward really depends on the gearing ratio tho

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)

b**'))) s s f P•

SMOKE

There's tape so it sticks and then gravity pulls it down and it repeats

Flat earthers theory confirmed: "the earth is after all one giant TURNTABLE.."

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

weird algorithm

the horses name was friday. Hope this helps

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.

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.

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.

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...

3v1

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

Number 3 is not 3 times. It's infinitely fast.

There is water in the mystery cylinder. I am sure of it.

0:33 _happy flat earther noises_

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?

Mercury

1. thors hammer (small) 2. lego 3. faster than i can ever run 4. idk now lets go see how correct i was...

1. Mercury in the Cylinder 2. Cycle go Forward 3. X2 speed of V1 4. Center part of the train go backwards

1. half honey, half air 2. backwards 3. infinite speed: 1round/v+1round/oo=2rounds/2v 4. (surrounding) air

tape paris london russia

1. Theres a hamster in the cylinder

3. Vavg = (V2 + V1)/2 Vavg = 2V1 = (V2 + V1)/2 4V1 = V2 + V1 V2 = 3V1 3 times faster

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.

@Tahzib Mashrik That's true, but it's stationary relative to the ground. Turns out I got a lot of answers wrong, haha.

The part of the wheel that is in contact with the ground is moving in the opposite direction to that of the train.

Honey in cylinder

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

thank you :)

1. water 2. forward 3. V2=3*V1 4. sides of spinning wheels

How are people getting 3 when my answer is Jupiter?

0:02 I'm sorry im going to have to pause here did you say "Palace of Discovery?" .... I'll be back

4) On the equator left to right or vice versa, 1) Magnets involved

1. Water 2. Forward 3. Thrice the ospeed for the first run 4.The Smoke(for diesel and coal engine trains)

the answer of 4 is "The wheels"

so ur not gonna put the answers in the video? fail

2:43 should be 3x faster then V1

1 a pendulum 2 backward 3 v1+v2/2 4 the train itself

1. An unbalanced center 3. 3×V1

0:33 FLAT EARTH CONFIRMED

1. Another Cylinder inside it?

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

Another small cylider inside that

sand

1. liquid with high viscosity 2. backwards 3. 3xV1 4. The wheels

Jesus loves you brochachosy

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.

@Jenna Tolls And why must you be so mean about it.

@Jenna Tolls I see my mistake now.

@Jenna Tolls Oops

00:33 - did Veritasium just go full flat earth?

4) circumference of wheel

number 3 is not a riddle just simple math

1. Theres a string thats circling 2. Forward 3. 1 4. The thing thats like a line

Cool!!!!!!!!!!!!!

WE STUDY PHYSICS JUST TO CRACK JEE😂😂😂

Imagine being so desperate for views so u make a 5 min vid in to 2 separate 10 min vids

What do people can try to answer the riddles, chill out man

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)

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.

The point of contact of the wheel to the rail doesn’t move backwards

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

@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

@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

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

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

1. water 2. stay 3. 3V~1 4. wheels

First lap 3 minutes second lap in 1

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

4. The rails

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

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.

v2 = 3*v1

4 =Wheels✓

wwo vapoer makes my man section hard like stonwe rock

1. Weight’s? 2. Stationary 3. Depends on your speed 4. Wheels

Well I guess a metal ball counts as a weight

Q4: Steam🙃

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

Honey

Am I wrong that his intro sounds very 2004 science show

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.

Think Inc.

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