For those of you following us on facebook, you will already be aware of the YouTube channel Veritasium because I posted on facebook last week about this awesome video. For those of you who aren't following us on facebook, why not? You're missing out!
Now, before I get on to the subject of this post, let me first say I really, really like Veritasium's videos. I thought minutephysics was the pinnacle of awesome when it came to internet science videos, but I have to admit that Veritasium challenges minutephysics for that crown.
Here is why. Minutephysics is awesome and entertaining (and I'm still a huge fan), but take a minute and think, how much does it really improve your understanding? It definitely entertains and therefore sparks an interest in the subject it is describing, but part of the limitations the author imposes upon himself restricts just how much understanding he can actually teach. I think (though James might wish to chime in with a different opinion) that people who watch Veritasium's videos will come away having actually learned more.
Here is why. Derek Muller, the man behind Veritasium, has actually done research (a doctorate, in fact) into what does and doesn't work when teaching science in videos. Most importantly he found that if you first of all explain the common misconceptions and why they are wrong, that people learn better. He actually found in his research that if people with misconceptions watched a video that only explained the truth they often come away even more sure of their misconceptions. Surprising, I know. I really encourage everyone reading to watch the video where he explains all of this - for me at least it made for fascinating viewing.
Has Veritasium made a mistake?
Anyway, here is a quick quiz. I think Veritasium has made a mistake in the video above. Can anyone spot it? Am I just being pedantic about this particular "mistake"? (I don't think so, I think it is quite important) Or is it me making the mistake and everything in the video is correct?
I know when I've tried to provoke comments in my posts before nobody has replied, so my hopes aren't high, but I'd really like to know whether other people can spot what I think I'm spotting.
Twitter: @just_shaun
Well I guess if he's talking about the mini-globe in Vancouver then that isn't spinning just because of inertia since it would eventually stop due to friction with the air. The stream of the water must impart some rotational force, unless people are constantly spinning it by hand! Is that what you're on about?
ReplyDeleteAlso, I guess when he says gravity has nothing to do with the Earth's rotation he is over-simplifying, since effects like the tidal force of the Moon influence it. Though I suppose because they're not the reason 'why it spins' (and I guess tidal forces actually slow it down) it's ok to leave them out of the video.
No, they're not what I'm thinking. While it is possible I will eventually be called a pedant over this, it is definitely more important/relevant than those examples.
ReplyDelete15 Trench points to the first correct answer!
He didn't really grow up in Vancouver, or even British Columbia?
ReplyDeleteBut seriously, I didn't pick up a mistake, and I watched it twice to try!
Strangely enough, when I was a kid I thought that we were held to the Earth because it spins. I have no idea from where I got that notion.
(By the way, I came here from a comment of yours at Cosmic Variance. I had a funny feeling that 'Shaun' was you, and I was right!)
Hi Rhys, thanks for commenting. I have to admit that the main reason I wrote that comment at Cosmic Variance was to see how much link through traffic we would get here. It turns out not too much in terms of raw numbers - though it brought you and your comment, so, hey, it was beneficial anyway.
DeleteAlso, I do apologise slightly for the level of crazy in the comment I wrote there. I wanted to get it written as quickly as possible so that I'd be one of the top comments! Although, I do think the extracting limitless energy from an inflaton has no problems with it in terms of principle (i.e. it doesn't violate any laws of thermodynamics) - although obviously it has enormous problems in terms of practicality. Sean Carroll has pointed out that the quantity of energy required to keep a 1cm^3 sphere of Higgs field at zero is equivalent to the mass of the moon, for example.
In reality, other than the fact that it is fun and silly to consider such ideas as a joke, I really don't like the line of thinking in the post I commented at. We should be making technological improvements in order to understand the universe better, not trying to understand the universe better to make technological improvements.
Searching for the Higgs boson gives the existence of humanity a shred of meaning, that's the only reason it is worthwhile to do. Whereas directionless technology doesn't add any meaning at all.
OK, I guess that's all the comments I'll get. My problem is this:
ReplyDeleteHe correctly states that inertia has a lot to do with why the Earth is spinning and that there is no force adding energy to keep it spinning, which is the misconception he is clearly trying to debunk. However, he also repeatedly states that there is *no* relevant force at all contributing to the spinning. He also has a big flashing message that says "gravity has nothing to do with it".
But in answering the question "Why does the Earth *spin*?", gravity is just as important as inertia. Inertia makes things want to travel in straight lines, not spin. It is gravity that provides the very necessary centripetal acceleration to cause the Earth to actually *spin*.
I do feel a little pedantic pointing this out, but his flashing graphic "gravity has nothing to do with it", at 2:15 when he says that the Earth does its thing "without any forces" and the final Star Wars text at the end are all a little misleading regarding what inertia actually is. If I turn all the forces off in a spinning object, it won't keep spinning.
However, I should add that the Veritasium guy does definitely understand the physics of it all because he goes into it all in another video about weightlessness in space.
You're right. I suppose he was implicitly considering the Earth to be a rigid body, and discussing the torque (that's my excuse for missing it, anyway!), but what you say is more accurate in the real world.
DeleteI think Shaun's point is a fair one which we discussed at some length in another setting. The reason I put up the 'gravity has nothing to do with it' graphic was because I was trying to spice things up and because I ran across the 'spinning creates gravity misconception.' I recognise that centripetal force is required to keep something spinning as a solid object but I don't think this is what anyone I interviewed thought. But looking at it in hindsight I would have preferred to do a better explanation that doesn't so categorically ignore gravity.
ReplyDeleteHi, thanks for the comment Veritasium. Your commitment to replying to people's feedback is impressive, especially on the videos themselves at YouTube.
DeleteThe 'spinning creates gravity' misconception sounds particularly frightening and worth trying especially hard to overcome. And, based on my impression from the video, I agree that nobody who answered "gravity" was thinking about centripetal forces. I would expect/hope that the message most people take from the video is exactly the one you're trying to present (i.e. basically, that because of inertia things don't need an input of energy to keep moving).
Thanks again for the comment... and, well, if you wished to write a guest post for us at any time then you would most certainly be very welcome.
" Inertia makes things want to travel in straight lines, not spin. It is gravity that provides the very necessary centripetal acceleration to cause the Earth to actually *spin*.
DeleteNo! No! No! The conservation of angular momentum is a form of intertia and that is exactly why the Earth spins. As the mass is drawn closer to the center, the conservation of angular momentum causes the body to spin faster - e.g. the ice skater spinning up.
Hi Michael,
DeleteThanks for the comment. So, I admitted right from the start that my point was a pedantic one, so I realise that this reply might seem pedantic to you, but...
I totally agree that, even without gravity, the Earth would have a constant angular momentum. However, the concept of rotational inertia only makes sense for rigid bodies that are held together by some force, otherwise all the individual particles of that body will travel in straight lines and the body will fall apart. For the Earth, that force is gravity. And therefore in order for the Earth to "spin", it requires gravity.
Even with the ice skater there are internal forces holding the body together, which are also necessary for the body to spin (and not, essentially, explode).
But, yes, this is a pedantic point I was trying to make, and the main issue Derek was trying to address in his video is exactly the one you are pointing out, which is that things don't need a constant force to remain moving. The difference is just me making a pedantic distinction between something actually *spinning* and something just having angular momentum... that's all.