The Motor Boat

Discussion in 'Physics & Math' started by Motor Daddy, May 31, 2013.

  1. Pete It's not rocket surgery Moderator

    I see... I thought you agreed with that assertion, since you didn't disagree. My mistake.

    So what speed do you think that your boat would travel at in still water? Or shall we do the experiment to find out?
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  3. Pete It's not rocket surgery Moderator

    Sorry, I didn't mean to ignore you

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    I'll disappear soon and then maybe Motor Daddy will engage with you.
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  5. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

    I have no idea, it's not linear like that. We need to MEASURE the speed of the boat in still water, like we measured the boat in current.
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  7. dumbest man on earth Real Eyes Realize Real Lies Valued Senior Member

    I did not think you were being mean. Knew I wasn't ignored because of speed change.
    Motor Daddy might will not "engage with" me because of me being Dumbest man on earth - I get that a lot of the time from really intelligent people !!
    Would hate to see you disappear though !
  8. Pete It's not rocket surgery Moderator

    I disagree. The proven principles of marine navigation adequately demonstrates that it is indeed linear.

    So do it.
    Toy boats are cheap.
    Pick a calm day, and a watercourse with a smooth current and measureable landmarks.

    Let us both stop talking about this and actually do the experiment, then return and compare results.
  9. Pete It's not rocket surgery Moderator

    Don't worry, I'll be back later!
  10. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

    Didn't you say before that GPS is more accurate and replaced the old-fashioned method?
  11. Pete It's not rocket surgery Moderator

    GPS is more accurate, but not perfectly accurate.
    It has mostly replaced the old method for convenience, but sailors can still rely on old navigation if their GPS gear fails.

    And in the situation we are discussing here, where we can see the embankment, there is no wind, are we're working with small distances (ie we're not sailing over hundreds of kilometres through open stormy water) then the old method is pretty much as accurate as GPS.

    And then there are submarines, that might stay submerged for days (weeks?) without access to GPS. How do you think they navigate?
  12. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member


    So there is 100% accurate, which we call "perfectly accurate."
    Then there is GPS, which is less than perfectly accurate.
    Then there is the old-fasioned method, which is less accurate than GPS, and way less accurate than perfectly accurate.

    Got it.

    Even a blind squirrel finds a nut every now and then.

    So as long as we forget about reality and play with your numbers the way you like then the numbers come close to working in certain situations?
  13. Grumpy Curmudgeon of Lucidity Valued Senior Member

    Motor Daddy

    A boat travels through water(and air, but it is usually a minor issue for boats). If it is stationary to the bank at WOT and we measure the current as 3.27k relative to the bank then the still water speed(at WOT)of the boat is also 3.27k(plus or minus airspeed drag effects, which are minor unless you are in a storm).

    Got it?
  14. Aqueous Id flat Earth skeptic Valued Senior Member

    No, there is no such thing. You can only be accurate to within the range of error of the measurement device. You can check the National Institute of Standards and Technology for more information.

    There is no such thing as perfect measurement accuracy. GPS goes to great lengths to give an accuracy that's adequate for finding yourself on a map. In the early days it had a classified mode that gave the military an ability to put ordnance through a radar antenna from 200 clicks back. It's nothing to scoff at.

    At present you have defined the accuracy requirement to be 0.01 km/hr. You did so when you settled on 3.27 km as your baseline. If you had said 3.270 km/hr, we would have understood that you require 1 m/hr of accuracy.

    Even a crude instrument can show you that the velocity of boat wrto the water, plus the velocity of the water wrto the bank, equals the velocity of the boat wrto the bank. Even Galileo understood this when he correctly stated this law centuries ago. Measurement accuracy has no bearing on the fact of the law.

    The converse is true. When you deny science, you are in denial of reality. Questions of measurement accuracy do not alter the fact that motion is relative.
  15. Pete It's not rocket surgery Moderator

    Not "way less". It is accurate. You do know that there were people navigating the oceans long before GPS, don't you?

    Do you think that explains how ships found harbour before GPS.

    Motor Daddy, I've invited you several times to actually do this experiment, which you have repeatedly ignored. It seems to me that you are just not interested in finding out what actually happens.
  16. Russ_Watters Not a Trump supporter... Valued Senior Member

    Note that while this is an important principle in marine navigation,* it is absolutely critical for airplanes, which carry a fuel load calculated in part based on the expected winds along the course. Since the jet stream travels 100+ mph, it can have a major impact on fuel consumption.

    *Though the past week people have been focusing on a special/simple 1-dimensional case, navigation happens in 2D and that's what navigation classes focus on. This week-long conversation takes about 30 seconds in a navigation class, if mentioned at all, before starting a 2D vector addition discussion.
  17. EinsteinHimself Banned Banned

    Does the boat turn around or is the current variable?
  18. James R Just this guy, you know? Staff Member

    Motor Daddy:

    I see you haven't made any progress in the past 2 weeks. Then again, you haven't made any progress in over 2 years, so no surprises here.



    Yes. The speedometer reads the boat's speed relative to the water. How could it know about any embankment?

    Relative to what?

    If you consider the boat stationary, then yes, the water is travelling at 11.27 km/hr relative to the boat when the boat's speedo says that. In fact, you've hit on an important fact here. The speedo is attached to the boat, see? And water flows past it. So, what the speedo actually measures is the speed of that water flowing past it. When the speedo says 11.27 km/hr, that's the speed the boat sees the water going by at. 'cos the speedo is, like, attached to the boat.

    And, by an amazing symmetry, guess what! Get this: the speed of the boat relative to the water is always equal to the speed of the water relative to the boat! How about that! This means that we can say that the speedo measures the speed of the water relative to the boat or the speed of the boat relative to the water. Useful, eh?

    Now, let's be very careful now. Let's think about something really really complicated. Let's think about the boat's speed relative to the embankment. What will the boat's speedometer tell us about that? Think hard. Think. Strain. Not getting it yet? Think really hard. Give up? Ok, don't hurt yourself. I'll tell you. The speedo tells us nothing about the boat's speed relative to the embankment. "Why not?", you ask. Because it has no way of knowing the embankment is there.

    Also, the speedo won't tell us anything about the boat's speed through mythical Motor Daddy "space", because it doesn't know that is there either.

    Got all that? No? Read it again until you have. Now, let's try to move on.

    Suppose the speedo is reading 11.27 km/hr and the boat isn't moving at all with respect to the embankment. That is, the boat remains level with somebody standing still on the embankment. How could that possibly be? Could such an unthinkable thing possibly ever happen in Motor Daddy's daily life? Surely not. Because that would imply that there might be - SHOCK HORROR - a current in the water. It might mean that the river was flowing past that embankment at some speed of other, and that the boat was trying to go upstream against it.

    Could we possibly deduce the speed of such a hypothetical current in this example? Surely, no ancestor of Motor Daddy could ever have accomplished such a feat. But could Motor Daddy himself make this mental leap?

    Let's think again, like REALLY HARD. First, of course, we need to work out what "upstream" might possibly mean, since that has been a sticking point for us in the past. Perhaps, unlikely as it may sound, "upstream" could mean the direction the water is flowing from, and "downstream" might even mean the direction the water is flowing towards. Or maybe "upstream" is just a meaningless term, never understood by any Motor Daddy in the history of the world. What do you think? Well, let's go crazy and assume that "upstream" has this meaning.

    Now, the speedo says 11.27 hm/hr, but the boat isn't moving past the embankment. The motor is doing work, but nothing's happening. What has gone wrong? Who's responsible? Could it be that this ... current ... could be -SHOCK HORROR - WORKING AGAINST THE BOAT?!!!! This current from...err.... this "upstream" place? No, hold me down! It's all too crazy!

    Because, if that were true, it would mean ... ah, oh, this hurts my brain! ... that the ... ugghhh... current would be travelling at 11.27 km/hr, and - HELP ME GOD! - that would imply that 11.27 minus 11.27 equals.... equals ..... equals. ... ZERO!

    NOOOOOO! It couldn't be true! My world is disintegrating around me. Help me, Motor Daddy Gods! Next you'll want me to believe that 8 + 3.27 = 11.27! It's messing with my mind. It can't be true!


    Time out.

    Let's back away from this strange affliction. Let's return to the common-sense Motor Daddy world, where all speeds are unrelated and nothing is relative to anything anywhere. Ah! I feel better already, don't you?


    We settled that the speed of the boat in still water was 8 km/hr, back in the opening post of the thread. Try to keep up. Think of it as the maximum speed possible on the speedo if that helps.

    No! You can't think like that! That almost sounds sane. Surely the boat's speedo must know about SPACE?!!!

    This is an impossible question to answer, isn't it Motor Daddy?

    Why would Pete even begin to imagine that such a question would have an answer?

    You couldn't begin to answer it, could you? It's impossible.

    It's all so confusing! Upstream, downstream, cross-stream. Who makes this shit up?

    I agree, Motor Daddy. The term "up the river" is meaningless nonsense. For that matter, "up" and "down" in general are meaningless, aren't they? Each direction of travel has a relative speed, so there's no way to tell up from down, rivers or anything else!

    What crazy person first thought to say "things tend to fall down"? What is this "down" business all about? That person must have been blank the river without a paddle.

    We'd need a Motor Daddy light meter to ever know. Because without one, we couldn't possibly know anything about SPACE, and without SPACE, we can't know anything about speeds.

    I'm a bit puzzled about how you can state that water is flowing past an embankment at 3.27 km/hr, though. Isn't that a relative speed? What's the water's speed through SPACE? That's what I want to know. Where did you get this 3.27 figure from? Did you measure it in SPACE? If not, why not?

    It's a wonder that Magellan ever made it around the world in his sailing ship. Or Captain Cook, who managed to find Australia more than once, starting from England. Just blind stupid luck, I guess. Or secret GPS satellites in the 18th century, perhaps.

    Let's face it. Nobody could ever really navigate anywhere before GPS. Not accurately. Oh no.
  19. Randwolf Ignorance killed the cat Valued Senior Member

    I love it James! Your best yet. Humour in the morning is great! Hope MotorDaddy appreciates it...
  20. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

    Good work, James. LOL

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    I've read your response and I've taken mental note of all the absurdities, untruths, fabrications, misunderstandings, and...sarcasms. I haven't calibrated my sarcasm meter lately, so it's a bit off...or maybe it's because I'm losing focus of your you haven't been here in sooo long that I was starting to think you abandoned this site. Maybe you were doing real physics somewhere in the Motor Daddy universe in which we live?

    The problem is...Pete. He bans me when I respond with truth, so what is Motor Daddy to do in a world of chaos and untruths in which truth is banned?? The way I see it, my only course of action is to simply not respond, because when I do respond with truth, I'm banned! It's akin to telling a Christian there is no God, can you relate? No response necessary...
  21. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

    I always appreciate James' response, he knows that. That doesn't mean I think he's correct, it just means that I appreciate tales of Santa and the Easter Bunny as much as the next guy. There's real value in being able to tell tall tales.

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    Last edited: Jun 25, 2013
  22. dumbest man on earth Real Eyes Realize Real Lies Valued Senior Member

    So, Motor Daddy, what is the TRUE ANSWER ?
    Can this Conundrum be put to rest yet ?
    In all consideration of my lack of intelligence, I thought I had figured out the answer a few moments after being presented the problem. To me it even seemed that if the full throttle speed and the speed of the current remained truly constant, it would have made NO DIFFERENCE if the first leg of the journey was UPSTREAM or DOWNSTREAM - as long as it was a ROUND TRIP !!
    Can understand if you refuse to converse with someone so much dumber than you - but I really am just trying to learn! Maybe, just this once, you might help out someone less fortunate in having been blessed with superior intellect.
    As an aside, I am at ease with others being more intelligent than myself. Can you say and mean the same? If so, are you also at ease with others being less intelligent than yourself? I would like to believe that you are NOT just using your superior brain power to play mind games with us less endowed!
    Sorry to take so much of your time.
  23. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

    The true answer is that if you want to know how much time it takes for the boat to travel 8 km along the embankment in each direction, in still water, at WOT, you measure the time. If you want to know how much time it takes for the boat to travel 8 km along the embankment in each direction, in current water, at WOT, you measure the time. TIME is linear and you need to measure the TIME! Speed is not linear in the two different scenarios. Power=work/TIME!

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