Risking My Life To Settle A Physics Debate

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References

Gaunaa, M., Øye, S., & Mikkelsen, R. F. (2009). Theory and design of flow driven vehicles using rotors for energy conversion. In EWEC 2009 Proceedings online EWEC

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Special thanks to Patreon supporters: Bill Linder, Paul Peijzel, Crated Comments, Anna, Mac Malkawi, Michael Schneider, Oleksii Leonov, Jim Osmun, Tyson McDowell, Ludovic Robillard, Jim buckmaster, fanime96, Juan Benet, Ruslan Khroma, Robert Blum, Richard Sundvall, Lee Redden, Vincent, Marinus Kuivenhoven, Alfred Wallace, Arjun Chakroborty, Joar Wandborg, Clayton Greenwell, Pindex, Michael Krugman, Cy 'kkm' K'Nelson, Sam Lutfi, Ron Neal

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Thanks to James Lincoln for building the initial prototypes for a model blackbird.

Written by Derek Muller, James Lincoln, and Petr Lebedev
Animation by Mike Radjabov and Ivy Tello
Filmed by Gene Nagata, Derek Muller, Trenton Oliver, AJ Fillo and Emily Zhang
Edited by Trenton Oliver
Additional video supplied by Getty Images
Produced by AJ Fillo

[veritasium]

If you want more detail on the explanation here it is:
1. The car is powered only by the wind. There is no motor or batteries of any kind.
2. The propeller does NOT spin like a windmill. The wind does NOT push it and make it turn.
3. Instead the wheels are geared to the propeller to turn it the opposite way, like a fan, so it pushes air backwards.
4. To start the vehicle the wind simply pushes on the whole vehicle (like a block of styrofoam) and gets it moving.
5. The wheels are turning so they turn the propeller in the opposite direction to how the wind is pushing it.
6. The prop is pushing air back so air pushes the prop forwards, accelerating the car.
7. Once you get up to wind speed there is no apparent wind on the vehicle. If the prop were spun like a windmill this would mean no more thrust. But, since the prop is operating like a fan, it still accelerates air backwards, generating thrust.
8. You can go faster than wind speed continuously because even when going faster than the wind, the prop can still accelerate air backwards (in the car's frame of reference) generating thrust. In a stationary frame of reference you would see that the wind behind the propellor is slower than the surrounding air. So it's clear that the energy is coming from the wind.

FAQ: If power is coming from the wheels to turn the prop, why doesn't that slow down the wheels more than it gets the prop to push back?
A: Because the wheels are moving over the ground much faster than the prop is moving through the air (because there's a tailwind).

Example: 
Let's say the car is going 12m/s in a 10m/s tailwind, so faster than the wind (note the prop will be moving through an apparent headwind of 2m/s).

Power = Force x Velocity

Let's say the chain applies a drag force of 100N on the wheels to drive the prop. This means we're taking power from the wheels = FxV = 100N x 12m/s = 1200W

If we apply this power to the fan, it can create a force of F = P/V = 1200W / 2m/s = 600N

Admittedly I've assumed no losses, but even if we waste half the power, we'd still get 300N of thrust which is more than the 100N of drag the prop adds to the wheels. The key is that we're harvesting power at higher speed, lower force, and deploying it at lower speed, higher force (which is only possible because we have a tailwind - in still air this wouldn't work because the relative velocity of the wheels over the ground would be exactly the same as the relative velocity of the prop through the air).

[frogsinpants]

"I expect a lot of pushback in the comments." That's okay, this thing is driven by pushback.

[Tluangtea]

When your online argument with random people is so heated you ended up building a vehicle that seems to defy logic....

[willh]

I was blown away that so many physicists called it fake or impossible.

[PIXXOD]

Now just give it a few years and we will have the first-ever cylinder earthers.

[COTU]

It's not breaking the laws of physics, it's breaking the laws of understanding.

[PotatoJet]

Sending this video to my mom! She’ll be so proud of for

[albertorip]

As a windsurfer already going (much) faster than wind while sailing sidewind seems magic, but the physic involved it's not so difficult in the end: just some vectors. The very brilliant thing here is to have made a device that can go "sidewind" while going downwind.

[eldyy]

The best part is even when they had a working model people on the internet told them it was impossible. If you have an idea you think will work don't let the internet stop you.

[nicholasstathopoulos]

"That's great in practice, but how does it work in theory?"

[sarahbezold]

this is going to become a trick problem on a physics exam.

[Siblo]

As a yacht racer and captain it took me 25 years to accept and understand apparent wind and going faster than the wind. So as a base level I think I already understand more than your average person. But I did have to watch every second to understand how this works. Mind still boggles.

[mantouedible]

Once you mentioned the "fan driven by the wheel" it really starts to make sense. Imagine that the fan is just a giant sail, then it would go down at wind speed; and by converting the energy at the wheel to the fan it gets this additional oomph that pushes it faster.

[skaruts]

lol true inventor spirit: _"how do I stop this?"_
_"you, uuh... I dunno, push the lever."_
_"which lever?"_
_"the one that stops it!"_

[timkimmel]

"JUST GO WITH WHAT FEELS LIKE IS SLOWING YOU DOWN"

[naveenlp]

8:05 was my absolute favorite part of the video. jumping from an intuition to an abstraction to a mechanical solution. amazing stuff

[isaacchock]

I had the same problem happen to me in a middle school science class… teacher asked if a plane could lift off if it was on a treadmill going backwards as fast as the plane going forwards. If the speed came from the propellers and not the wheels then it shouldn’t matter if the wheels were turning backwards…
I was the only one in class saying the plane would lift off. Interesting thing (taught me a lot about people) is that I got threats and was even on the receiving end of violence when I would not change my stance.
When we watched a mythbusters video that showed the plane did lift off they still wouldn’t believe and continued to threaten and bully me.

Perhaps the most dangerous people in our society are the ones who think they know and will not listen.

[flatfourtwenty]

The inventor must have been grinning so hard in that shot where he's holding the wind sock. Basically got the best shot possible with great equipment that he was right all along.

[alecmalisheski]

Experiments made out of spite to prove people wrong is the best kind of science

[craighaldane]

Amazing. One of the best things I've seen for a while👍. Absolutely loved it.