Built on Facts

This Saturday I’m getting married! The following week I’ll be in Barbados relaxing on my honeymoon. While Barbados is a highly developed Caribbean economy with no shortage of internet access, in the interests of relaxation and matrimonial bliss I shall not be online. Posting will resume the following week.

Until then, I’ll leave you with this Wired article about a wind-powered car that travels directly downwind faster than the wind. When I first read the idea, I thought “No, that’s an obvious violation of the laws of nature and everyone involved is an idiot.” Well, the proof is in the pudding and if you don’t find the physics explanation particularly intuitive (I still don’t really intuitively grok it, though I get the idea), the fact that they actually built and drove the thing at about 3x wind speed settles the argument.

Perpetual motion guys take note – on the off chance we’re wrong about conservation of energy the way to get our attention is not with long-winded emails about some grand conspiracy, it’s to build the thing and park it outside a physics building. After it keeps running for a few weeks I bet people will pay attention. But personally I’d strongly advise you that there’s better uses of your time.

Anyway, see y’all around!

Comments

#1 hymenoplasty surgery
September 2, 2010

Wow! Congrats on the marriage! I’ve just shared the link to the prop car on fb. I can see how the perpetual motion folks can get their heads in a tizzy. I’m not sure myself how it works!
#2 ERV
September 2, 2010

YAY!

Congratulations, Matt!
#3 dWj
September 2, 2010

Congratulations! I got married four weeks ago. We’re doing our honeymoon in St. Croix in February.
#4 Fro
September 2, 2010

I’ve never commented before but have been reading for some time now and figured this was as good a reason as any. Congratulations on your upcoming marriage. As a meager gift, accept by gratitude to you for having one of the most interesting blogs out there. I read it religiously. You have a way of explaining things that make me look at math functions I studied during my mathematics degree in an entirely new light.
Blessings to you and yours. May you continue to share wonderful times together, and enlighten the greater internets with your insight. Thanks again for having a great blog!
#5 Markk
September 2, 2010

I love how in the wired story slides in the fact that the builders used their -knowledge of physics- to build the car yet the article somehow has them set up against academic physicists. The physics community roundly thrashed Mark from Good Math Bad Math when he put forth the idea wrongly a while back.

This is a beautiful engineering exhibition of how our physical models have non-intuitive predictions.
#6 Ethan Siegel
September 2, 2010

Congratulations, Matt!
#7 Luis
September 2, 2010

Congratulations Matt.

Neither I post comments often, but am fan. I am biologist with a bit of training in math and physics, your blog has really contributed for me digging up some long forgotten maths skills and applied them to my research projects. Thanks for taking the time to write!!

Best wishes,

Luis
#8 Omega Centauri
September 3, 2010

Pretty cool concept. The thing that seems baffling is that you expect the vehicle has to have net drag. If it has net drag, it cannot match (downwind) the speed of the wind. So somehow the blades are moving fast enough at mostly a right angle to the wind, to produce downwind thrust. That means that the net aero drag force car+blades is actually negative! At the same time energy is being extracted from the wind, so the wind feels positive drag. [I better stop now, or I'll get a headache]. It must be related to the fact that wind turbine blades tips are moving at several times the wind speed. Several times wind speed means you can change the apparent angle of forces by a lot!

Now, I have a question. Can it accelerate from less than windspeed, to above windspeed going directly downwind all the way? Or does it need an initial push to faster than the windspeed? [Going sideways to the wind to gain speed, then turn downwind is cheating...]
#9 Magnus
September 3, 2010

Congratulations!
#10 complex field
September 3, 2010

Congratulations!

Re: wind powered car, cf sailboats.
#11 rob
September 3, 2010

yay! wedding!

boo! you get to go to Barbados!
#12 Uncle Al
September 3, 2010

Nuptual congratulations! Non tamen solam intendit interiorem, immo interior nulla est, nisi foris operetur varias carnis mortificationes.
#13 raghuvir jha ( india )
September 4, 2010

congratulation matt springer for your marriage . may god bless your marriage life. i wish your happy and prosperous life.

enjoy your marriage life but don’t forget to write blogs !!
#14 Rick Cavallaro
September 5, 2010

> Now, I have a question. Can it accelerate from less
> than windspeed, to above windspeed going directly
> downwind all the way? Or does it need an initial
> push to faster than the windspeed? [Going sideways
> to the wind to gain speed, then turn downwind
> is cheating...]

Yes, it can start from a dead stop and accelerate to about 3X wind speed going directly downwind the whole time. It can then maintain about 3X wind speed until the wind stops of the mechanics of the vehicle fail. I’ll post a link or two.
#15 Rick Cavallaro
September 5, 2010

First Ivanpah run:

Second Ivanpah run:

Video shot by Richard Jenkins from the back of chase vehicle at El Mirage during the NALSA runs:
#16 Rick Cavallaro
September 5, 2010

I posted three links to videos showing the cart self starting and achieving DDWFTTW. It looks like the links put the post in the moderation queue.
#17 Jr
September 5, 2010

Congratulations!
#18 Kaleberg
September 5, 2010

Congratulations on your wedding. Have a great time in the Caribbean.

The sail car makes sense. Imagine a wagon with a sail. The wind can push it at wind speed. On deck, it feels like you have gotten all of the power out of the wind. The sail can only capture so much, but the wheels are turning because of friction with the ground. If you could use that energy, you could go even faster than the wind, though you’d have to trim the sail to cut the friction once you outrun it.
#19 CCPhysicist
September 6, 2010

Congratulations!

It’s not a honeymoon unless you leave the computer at home.