Spinning Tube Trick

[Applause] Check this out! I have a piece of PVC electrical conduit, and on one end I've labeled an O, and the other end I've labeled an X. Now I'm going to put it on the table and press down with my forefinger on the O, and I'm going to give it a [Applause] spin. Do you see that? You can only see the O as it spins around.

Let's make sure that's not just a fluke. I'll try it again. So putting my finger on the O, and I see only O's. Well, let's try putting my finger on the X and see what we see then. And we see only X's. So why is that? Why do you only see the label of the side that you press? Well, I don't want to tell you the answer right away. You could Google it, but I don't think that would be very satisfying.

So I think the best way would be to go down to your local hardware shop, pick up a bit of electrical conduit, and cut it into various lengths. Now, to help you out, I have made a shorter length of tubing with the same markings on it. So let's give that one a try and see how it compares. So first, I'll press on the O. We see three O's when I do it like that, right? But you don't see the X's. Yeah, but if you put your finger on the X to start with, you see three X's. That's interesting.

So what's the deal? Yeah, what is the deal? If you like, send me in a video response, and I'll post it below. Now if you're too lazy for any of that, I'll post the answer in a week, so you know, subscribe, and you'll find out why this happens.

So normally when I'm filming my videos, I have to approach people and ask them to talk to me about physics. But while I was filming the spinning tube trick, a few kids came up to me and wanted to see what I was doing, and we got to discussing how the trick works. One of the kids suggested that I try spinning the tube on a glass table.

Now, a glass table is beyond the budget of Veritasium, but a piece of glass resting precariously on the backs of two chairs? That I think I can manage. If this was glass and you clicked on the X and we were looking from below, you'd see the—you're hectic jar. I reckon you'd still see the X's. I reckon you still—I don't know, but I mean, I reckon you still see. Good question!

Next video! This is the next video. We need to—now instead of saving this for another episode, I thought I would do it right now, and that way you may have a little bit more evidence to figure out how the trick is working. So I'm going to place the tube on the glass surface, and I'm going to press down on the X. I want you to make a prediction.

If we look from the underside, from underneath the glass, what will we see? Will we see an O, like the student thought? Will we see an X, like I said we would? Will we see both the X and the O, or will we see neither? So I want you to make a prediction now. Click on one of the annotations if you're watching on YouTube. If you're watching on a mobile device, I'll put the link in the description, so hopefully you can check that out.

Let's give it a shot! So make your prediction now. 3, 2, 1!