Comments by "bruzote" (@bruzote) on "A Physics Prof Bet Me $10,000 I'm Wrong" video.

  1. Don't get too cocky. We often think we understand something...until we realize we don't. ;-) If you have not learned that yet, wait until you experience more challenging problems to eventually teach you that lesson.
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  2. I am laughing as I imagine this happening (after unintentionally installing the windmill backwards) during a well-attended demonstration of the original idea. That would look funny. Slightly forward, then back. Oh, wait, forward! No...back.
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  3. No. Even in an optimal scenario, wind can only APPROACH the speed of light. Matter cannot travel at light speed. So in your hypothetical case, the car would still travel faster than the wind without hitting light speed.
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  4. He may have gotten so carelessly cocky BECAUSE he is a Physics Professor at UCLA. He figured he didn't have to challenge himself if some YouTube guy seemed wrong. Either that, or their is some behind-the-scenes agenda we don't know about. That is always possible when money is involved.
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  5. I was thinking the same thing last night about the torque. The issue becomes one of how much power one can capture from the propeller at any given speed versus how much power is lost moving the car forward.
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  6. I don't think so. I thought of that myself. However, the sails that are tacking through the wind are fixed to the boat. In this case, if you think of the windmill/propeller blades, they are moving with respect to the boat as well as the wind. That breaks down analogy. Put another way, the only way to capture energy FROM the wind is have it do work. The wind CANNOT do work if it is not pushing so that a COMPONENT of the wind's vector is aligned with a COMPONENT of the sail's equal-and-opposite "resistance vector". (In fact, the two arise from each other.) For a tacking sailboat, the downwind may push on the sail, but the component of the downwind that is pushing is actually just the part that is perpendicular to the sail (the part doing the basic pushing, as the problem gets more complex when you treat the sail as an airfoil). The pushing component of the downwind is thus not completely aligned with the downwind's overall vector. In fact, that component may be nearly zero if the angle is extreme, BUT IT IS STILL POSITIVE FORCE AVAILABLE FOR USE BY THE SAIL. That pushing component of the wind transfers to the sail. The sail then transfers that push to the boat through its own force vector. However, just like the wind, the sail then has a pushing component that aligns with the boats forward direction and part of it aligns with a cross-course direction. The direction of the sail force component that is pushing the boat forward can be anything less than 90 degrees from the overall force vector direction from the sail, which itself can be anything less than 90 degrees from the overall force vector direction from the wind. Thus, the boat can move in ANY direction less than 180 degrees from the wind (assuming enough energy is captured to overcome resistance losses)! Of course, since the boat is only using a component (part) of the sail's pushing force which is itself only a component (part) of the wind's pushing force, the boat is going to capture less POWER from the wind than a boat moving downwind. However, a boat going downwind may have more power and approach the windspeed in shorter time, the downwind sailboat that reaches downwind speed will have ZERO more power available to accelerate. It cannot exceed downwind speed. Meanwhile, the tacking sailboat will capture much less power from the wind and it will accelerate more slowly. However, it will also but continue to accelerate until it is going FASTER than the windspeed (assuming the ocean waves don't slow it down too much). It is a trade-off of speed vs power, as counterintuitive as that sounds.
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  7. As for holding the car in place, isn't that like pushing the car over a non-moving treadmill? If you're pushing, then that is cheating.
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