That guy absolutely did do his homework, he was just arrogant and wrong. He was the one who insisted in making the bet so public in the first place.
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More than anything else, as a physicist I’m embarrassed by proxy by his mistake. Can’t even blame the Dunning–Kruger effect; he absolutely should have known better.
The best thing I can say about him is at least he paid up.
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Sorry for the pedantry, but don’t you mean kinetic energy, not potential energy?
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You’re right. It’s energy of relative motion, thus kinetic. Mea culpa.
And don’t worry about the pedantry. That’s a fundamental error on my part, not a nitpick. There’s nothing to forgive.
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A standard sailboat cannot go direct downwind faster than the wind, either on water or on land. You need the propeller thingy geared to the wheels, or another way to vary the gear ratio between the air speed and land speed.
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It can if it is close hauled (About 45º against the wind) to reached (90º). I never said anything running downwind, that is very inefficient.
When sailing with wind coming from the side the speed of the boat is not relevant to the force the wind creates on the sail.
The force of the wind on the sail pushes the keel against the water causing the boat to slide forwards. With enough force on the sails and little enough friction the boat can go faster than the wind pushing it.
Same with the Blackbird: Don’t think in absolute speeds, think in kinetic energy and relative speeds.
But that is the premise of the blackbird and this challenge. Thinking about it like a sailboat is exactly how people are led astray on this because it has positive acceleration even when the relative wind is zero, while a sailboat does not.
As good an explanation as I’ve seen here (mind the potential/kinetic clarification).
Thank you.
I can’t help my mind straying towards –– isn’t this a compelling model for a starship drive? In space the issues of friction and drag fall away, and the potential of leveraging a differential seems very compelling, particularly when it means reducing the load of fuel dramatically. I’m just not sure of the medium, and what you leverage? Solar radiation? Gravity? Dark matter?
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I don’t think so. At the very beginning, the rotor is stopped and the wind pushes the vehicle forward just by drag. But as soon as it starts moving, the wheels turn the prop and it begins pushing air backwards.
I posted a lot of statements before I looked at it closely –– my own fault for not looking at what I did not realize was much more interesting than I expected. Sorry to waste your time correcting me for the obvious.
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Exactly. Towards the end of the video he does a completely mechanical demo with a wooden roller contraption between the floor and a moving board. In some sense, the wind powered part of this is a red herring, I highly recommend anyone confused about this go watch that demo and ignore the complexities of wind and propeller aerodynamics.
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Earth or the relative vacuum of interstellar space isn’t really the issue. Think of it this way, there has to be energy to extract and a mechanism for converting it to do work. If you want to move something you need something to move it. Nothing comes from nothing, as it were. If you want to drive a vehicle between stars, you need an energy source to drive it.
I think sometimes the confusion derives from what motion really is. You wouldn’t expect a cause without an effect, would you? On a really basic level, the conservation of motion is the logic of causality.
I haven’t seen the original video, but my guess is that the creator of Blackbird wanted the car to be free of all electronics, to dispel any claims that it could only be done with a motor.
If that’s what you took away from the video, you should watch it again. But it’s true that this video doesn’t explain how the car speeds up from below-wind-speed to above-wind-speed.
When the car is stationary, the wind is pushing on the car itself. The wind would actually put some force on the fan blades to try and make them turn clockwise, but the forward motion of the car, and the coupling of the wheels to the fan blades, actually makes them turn in the opposite direction.
As the car moves faster, the fan blades move faster. They never slow down or switch directions as the car transitions from moving slower than the wind to faster than the wind.
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No, but space does away with the friction and aerodynamics that limit this blackbird model.
yes - which is why I wonder what medium there could be in space that could be leveraged.
and you haven’t read all the posts yet - but thanks.
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Sorry, I was editing my post as you replied. I should have deleted and re-posted.
but this is like a sailboat - and not like this blackbird kart.
