Under the ruler 3: tilting the ruler

[TomusMedia]

please do audio books!

[AlexRaato]

MIND == BLOWN



[wantapgt]

@Steviewonder74CEA it's just ignorance that causes most "fake" comments. It amuses me too. Instead of taking the time to use their mind to understand concepts, the ignorant just refuse to acknowledge the possibility and call "fake." Sad sad people.

[MrRubixTV]

@UTJhn.  Thnx, that really helps

[steviewonder74CEA]

I find the fact that this has accusations of being fake very funny. If a person was going to lie... it wouldn't be about this.

[UTJhn]

As for keeping the cart still while moving the ruler and 'ground' (i.e. paper), I can think of one relatively simple solution. It would require building a second identical cart, and attach its frame to your table. The paper would go under the reels of both carts and the ruler would sit across both wheels. The fixed cart would provide the proper relative movements for the paper and ruler to keep the second cart stationary. As a bonus it would force the ruler horizontal as well.

[coolaun]

@UTJhn That's a very good idea. Unfortunately I don't have the elements to make a second identical cart: the cart was just made from bits and pieces I had around the house. Maybe I could find enough other bits and pieces to make a cart with the same dimensions.

[UTJhn]

@coolaun

Glad you liked the idea. Sorry you don't have the parts. That possibility had occured to me, but I dismissed it. The parts seemed like they should come in larger numbers.

An alternative would be to make 2 new carts, but I think the one you have has become an icon and it would be a shame not to continue with it.

[UTJhn]

@coolaun

Having the fixed cart look different might actually be good. The only critical thing is the radius ratio. Having the same height would be nice, but a tilted ruler can work (the tilt affects the ratio, but it is the same for both carts). Alternatives are a ruler with an offset parallel attachment, or a "ground" with a step in it. A stack of papers can provide a step of finely tuned height. The height of the cart itself could be adjusted some if the reel base length was variable.

[UTJhn]

Great videos! I think yours are the best demonstrations of the linear differential gear principal that the DDWFTTW cart uses. I might have been tempted to try to make such videos myself, but they wouldn't hold a candle to yours.

[drawnasunder]

Coulan: I understand the effect of the spindles' inner/outer radii, and *in general* I understand the analogy to the cart-downwind-faster-than-the-­wind. But could you please explain: on the wind-driven cart, what is mechanically analogous to your cart's inner/outer radii effect? Is it that the blades' angle of attack (or "twist"?) causes a rpm/unit of windspeed greater (or less than?) rpm/wheel circumference or some such?

[UTJhn]

@drawnasunder. Yes, if the wind cart has a 1 to 1 gear ratio (wheel rpm=prop rpm) then the prop pitch needs to be less than the wheel circumference. 1/2 the circumference to have the same ratio as the cart in this video. If the pitch and circumrference are equal, the same effect can be obtained with a 2 to 1 gear ratio such that wheel rpm= 2X prop rpm.

[MrRubixTV]

@mox1211 & @apocalyptica

[apocalyptica003]

@MrRubixTV,

Imagine the ruler being bent up into a wheel. The edge would still be going the same way along the big wheel, but the ruler-wheel would be moving anticlockwise...

[TheEditingShop]

Have you ever considered presenting children's television? You would be perfect and you'd be very educational and entertaining.

[CoolDudesJunk]

Love the vids :) You should really be on the radio with a voice like that.

[person4646]

This is an amazing little machine. I admit I was not able to wrap my head around the possibility of the inner vs. outer radii ratio making all the difference without cheating and reading these previous comments...nonetheless, I wanted to congratulate you on making such a cool machine.

[PuggleKid]

THE CART DOES ALL!!!!!!!!!!!

[PuggleKid]

Terrie Rocks!!!!!

[Buhnanah]

Can you just explain to me how this works?

[MrRubixTV]

@coolaun. I understand why the cart goes faster than the ruler - the ratio of 2:1 between the outer and inner radius of the cotton reels.

But why does the big wheel move against the ruler in the first place?

[mox1211]

@MrRubixTV Because there's 1 gear between big wheel and ground, it can't spin clockwise when puched right by ruler. The ruler, therefore, has the effect of pushing the entire system to the right. The ratio then dictates the relative speeds.

[UTJhn]

@MrRubixTV. I don't know if you are still seeking an answer, or if you are still checking here. If so, I hope this helps. The big wheel and the cotton reels counter rotate, so the big wheel must go against the ruler or the reels must go against the paper. Since the ruler is connected through the big wheel to the smaller diameter part of the reels, the paper has the leverage advantage and dictates the direction of rotation.

[HiroTheWonderDog]

Great stuff. You should also consider narrating a "Thomas The Tank Engine" video.

[xKingTLegendx]

hs voice makes me rele sleepy

[MrRubixTV]

His voice is weird, but nice

[skinnymcpenny]

Rate this commment a thumbs up if you want more vids AND his voice makes you sleepy :)

[gct7788]

skeptics = pwned

[kizzaDDD]

Omg nadahere or watever it is give the guy a break, and even if he is wrong, it's YouTube, hoos gonna care???

[nadahere]

But there is an angle at which the device will cease to move underneath/into the ruler because this system is based on friction. It is primarily dependent on the size of the center wheel but all the ratios come into play, as I commented in your previous video.

[junesue1205]

@nadahere nerdrage much? lollolololo

you're probably just jealous your voice isn't as awesome as this guy's

[pjuwmkp]

your voice is sooo relaxing. sometimes when i cant fall asleep i turn on the best of youtube podcast of ur video and it knocks me out lol.

[wesjb94]

same!

[beeeeeeenman7]

plz plz plz make more, your voice is freakin sweet

[GCmaster5000]

the ruler is always going to be on a tangent point on the wheel. tilting it shouldnt make a difference.

[theStadiumUstreamers]

exactly.

[ferretzrock]

i love your animal friends, they remind me of when i was kid. i'd love to see more from them and you!

[GamingGuy118]

I still can't get my head round why this works...

[bobaduddle]

How come when I try this the wheels cancel out and it does not move? Then I tried tilting it and it worked

[coolaun]

If the wheels are "cancelling out" it's probably because there is little or no difference between the outside and inside radii of the cotton reels. Here, the inner radius of a cotton reel (where the blue wheel touches it) is approximately 1/2 that of the outside radius (where the reel touches the surface on which it rolls).

[GymnasticsISlife96]

i always understand what you are saying. You sound very patient and you explain it well :D

[BlockHeadStuff]

Your voice is so kind a patient please make more videos your voice is hyponotizing :-)

[Dsdude2222]

i know right?

[TheEditingShop]

Seriously, this guy can teach me anything, I'l let him! I've never been this close to being hypnotized before. . .

[132ally132]

i like the toys

som peeple will say it is childish but it just helps you learn more make more vids

[sacredsword42]

please make more vids they are addicting, I want u to teach me everything there is to know!!

[sacredsword42]

great vids, u have the coolest voice and accent ive ever heard

[mortimorec]

Please make more your videos are really great, your voice and the stuffed animals make it seem like Bagpuss or something like that. Terrific!

[JoasMartin]

Please continue with your videos. You are the ebst teacher I've ever had!

[chaumas]

I want you and your animal friends to explain everything about the universe to me. I cannot explain why, but your videos have an almost hypnotic quality to them, and your way of explaining these things is very easy to follow.

[glokkpod84]

You could be the new Mr. Wizard or Bill Nye!

[UNOATL]

lol NERD FIGHT BELOW WARNING!!! :) jk guys

[ThanatosMace]

It obviously has nothing to do with angles or even force! There are only three variables in this problem.

Angular velocity (speed of wheel spinning)

Translational velocity (speed of wheel's movement)

Radius (size of the wheel)

T

[ThanatosMace]

The speed of the translational velocity (v) is the angular velocity (w) times the radius (r).

When two wheels touch, the point where they touch must have the same translational velocity (V1) such that (V1)=(W1)*(R1)=(W2)*(R2).

The trick here is that troublesome spindle. Notice it is thinner where the large wheel touches compared to where it touches the ground. Its radius changes, so conceptually there are five wheels (two smaller wheels for each small wheel) rather than three in this machine.

[coolaun]

There are three wheel sizes to be taken into account:

- r1 = radius of top wheel

- r2 = radius of inner part of cotton reel where the top wheel touches it

- r3 = radius of outer part of cotton reel that rolls along the surface

In fact r1 has no bearing on the speed: you can change the size of the top wheel and the machine will function exactly as before. What counts is the relation between r3 and r2.

[ThanatosMace]

Haha! I just solved this and refreshed the page to find that you've stolen my thunder! I had fun working it out regardless.

It's fascinating that the larger wheel's radius is irrelevant. Like you said, the ratio of the cotton wheel is all that matters:

(inner radius)/(outer radius)

I think what confuses people is the reference frame. If you moved the camera at the same speed as the machine, I wonder if more people would understand?

Thank you for such an interesting problem!

[coolaun]

I would love to find a way to have the machine stay still with respect to the camera! I do show a different reference frame in "Under the ruler 2", by making the ground move instead of the ruler, but I couldn't find an simple way to keep the cart still while moving the rest.

I appreciate the comments: I'm happy when this gives people food for thought.

[UTJhn]

@coolaun

Great videos! I think yours are the best demonstrations of the linear differential gear principal that the DDWFTTW cart uses. I might have been tempted to try to make such videos myself, but they wouldn't hold a candle to yours.

[etheoharis]

OK READ THIS MR. COOLUAN!

ITs not the tilt on the ruler that makes the difference. It the side of the ruler where you put the most pressure on! Right?!

Let me see you demonstrate that one!!!!

[coolaun]

Just try it yourself! You could make a simpler setup with just a single rolling wheel underneath a ruler. Moving a ruler laterally over a single rolling wheel will cause that wheel to move at 1/2 the speed of the ruler. Now try to make the wheel go to the right or left by putting more pressure on one side of the ruler...

[doughnutdoofus1]

this is completely irrelevant to the video, but your voice is lovely ^^

[ishwarrior]

Your voice would be excellent for audio books! Great video by the way.

[DrNate89]

The torque on the wheel does not translate to a force that overcomes the force of the static friction created by the ruler on the wheel? Is this static friction applied to the apparatus as a whole? I'm trying to figure out how to calculate this correctly, it's blowing my mind! Time to break out the physics text?

[coolaun]

There's no need to overcome static friction: the wheels (both top and bottom) are rolling. The only friction in play here is the friction necessary to stop the wheels from slipping. It's a gearing system, using one motion to produce a faster motion, just like a bicycle or an egg whisk.

[DrNate89]

The static friction I was referring to is that between the ruler and the wheel =) There must be two opposing forces in this model in addition to the gearing system, otherwise it would make too much sense :D

[coolaun]

The top wheel is rolling along the ruler, not sliding, so doesn't have to overcome any static friction. If the ruler were to be replaced with a rack and the wheel with a pinion gear, the machine would work the same way.

[DrNate89]

The ruler creates a force through static friction (which translates to a torque in the wheel or a force on the overall body), I just wan't sure what to name that force.

[rockandroses4u]

Thank you for posting these.I'd of never guessed that something like that happens. They're brilliant and neat :]

[somenglishguy]

These Videos Are Cool!!!!

Say Hello To George For Me!!!!!

He Is So Cute!!

[mrh3nrik]

Seriously, your videos are brilliant. There's even a monkey with a silly hat. You ought to get your own science show or something.

[LauridsG]

weird....

Somehow your voice makes me feel comfortable :)

[wmcwhinney]

Why do people with British accents seem more intelligent????

[gracedechoes]

sounds like a german accent to me...

[ThePlaneIsOnFire]

Once again, superb narration!

[red7z7]

oh hay guise look its physics

[jonasfoe]

What happens if the lower 2 wheels are bigger than the upper one?

[gct7788]

See the response from the author above... It would have no effect.

Only the ratio of the radius of the inside of the spool to the radius of the edge of the spool matters.

[TempusFugitive]

Very enjoyable video! Thank you!

[pocketmonkey101]

witchcraft! lol but seriously that's a pretty cool toy.

[ProPiracyAccount]

Please make more :D

[kravoc]

I love watching youre videos! just a matter of time until youre a youtube celebrity.

[Maxmaxz]

Merry Christmas to you, Flossy, Ethel, Carlos and everyone else who takes part in the science of rulers and wheels.

[thejeran]

MORE! (Love your voice)