4 Revolutionary Riddles

RubyRuby

5 weeks ago

Transcript

00:00At the Palace of Discovery in Paris, they have this huge turntable where you can

00:06sit and perform experiments, like in the middle of the turntable you can put some

00:11water and then add liquid nitrogen, and this creates a kind of fog, these tiny

00:15water droplets that spread out from the middle. But because the actual linear

00:19speed of this turntable is increasing the further out you go, well the vapor

00:25falls further and further behind, creating a swirl that looks a little bit

00:29like a hurricane. And that analogy is not by accident, the earth is after all one

00:34giant turntable and the weather patterns we get are a result of that. When you

00:40study physics in rotating frames of reference or even just rotating bodies,

00:44you find some pretty mysterious and counterintuitive phenomena, which is why

00:49I'm dedicating this video to four revolutionary riddles. Number one, here I

00:55have a ramp or an incline plane, and just to show you I'm not doing anything funny

00:59with it. If I just let a roll of tape go, it will accelerate down the ramp. But here I

01:06have a mystery cylinder, and I'm gonna place that on the ramp, and we will see that it

01:12rolls, and then it stops, and then it rolls, and then it stops. So my question to you is

01:21what is in the mystery cylinder, what is this object? Number two, take a bicycle and have

01:32someone support it so it doesn't fall over or lean it up against something, and

01:36then take a bit of string and tie it to the bottom pedal. Now what I'm gonna do is

01:41pull backwards horizontally on this string, and I want you to predict what the bike

01:47will do. Will it go backwards, forwards, or will it just stay there and not move?

01:54My intuition would tell me that it would go forward.

01:58I think it might not move. If you're gonna be pulling backwards from a stationary

02:01point on the pedal, you're gonna be pulling it backwards just as the pedals

02:05are trying to spin the wheels forward. So maybe it might not move.

02:09I think it's gonna go forward. I'll go with forward.

02:12You sure? Yeah, I'm sure.

02:14Alright. Three, two, one.

02:18Number three, I want you to think about running two laps of this track. Now the first lap you can go as slowly as you like.

02:25Let's call that speed V1. But on your second lap, I want you to run faster, such that the total average

02:32speed for both laps combined is twice V1, twice the speed of your first lap.

02:38So the question for you is, how fast do you have to run that second lap so that your total average speed is 2V1?

02:47Number four, anytime a train is moving, either slowly or very fast, there is a part of the train which is actually

02:55moving backwards with respect to the ground. That is not backwards with respect to the train.

03:01And it doesn't have to be going so slowly that if you ran backwards, you would be going backwards with respect to the ground.

03:07It is at any speed, any normal train will have a part of it which is moving backwards with respect to the ground.

03:16My question to you is, which part is it?

03:19Now, with these four riddles, you can make me a video response, if you like, to tell me about your solutions to them,

03:26or you can simply leave your answers in the comments below and number them one, two, three, four,

03:31so we know which ones you're talking about.

03:33And I will post all of the answers up next week, same time, same place.

03:39All of my videos are made possible by my patrons on Patreon.

03:43So if you are one of those people, thank you so much for your ongoing support.

03:47And if you're not, maybe now is a good time to consider becoming one.

03:51If you go to patreon.com slash veritasium, you can support me there.

03:55Otherwise, if you're interested in more riddly-puzzly things, you can check out my spinning tube trick,

04:01my five fun physics phenomena, and, say, the spinning disc trick.

04:05And if you haven't subscribed to Veritasium already, I highly recommend you do that.

04:08And since I'll be posting the answers next week, I would like for you to ring the bell down below,

04:15and that will make sure that you're notified when my videos come out.

04:19So, as always, thanks for watching.

04:21Wait, that's Michael's line.

04:23I heard Michael's line.

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