Cheshire cat Posted August 25, 2016 Report Share Posted August 25, 2016 As I understand it Junior and the rower were travelling in the same direction. Each needs to look after themselves. I don'y think the rower will get very far with a claim for whiplash. Link to comment Share on other sites More sharing options...
MtB Posted August 26, 2016 Report Share Posted August 26, 2016 The one that hit me was a single, so really he either needs a lookout or to turn round and face the way he is going. This seems very sensible. By having to push the oars the rower would find himself going slower, and he could also see where he's going. Wins all around! Edited to add that there are mirrors but these are generally regarded as needed for old people. In rowing that's anyone over 27! Ah, a bit of a 'pride' thing then. Anyone using a mirror is a wuss! A bit like bow thrusters on narrow boats then )) Link to comment Share on other sites More sharing options...
Jrtm Posted August 26, 2016 Report Share Posted August 26, 2016 Oh, come on! Surely you have been been traumatised? At the very least you must have suffered some whiplash? Get your claim in here!!! http://www.slatergordon.co.uk/personal-injury/road-traffic-accidents/whiplash-injury-compensation-claims/?infinity=ict2~net~gaw~ar~77160673357~kw~claiming%20whiplash~mt~p~cmp~S%26G%20|%20PI%20|%20Google%20|%20Road%20Traffic%20Accidents~ag~S%20%26%20G%20|%20Google%20|%20Whiplash%20Injury%20Claims&gclid=CJT5rf2q3M4CFVXGGwodLpoCKg Dont forget to add how worried you are about boating on a river incase this happens again and your getting sleepless nights over it! Dont forget to mention that he was going as fast as possable and was aiming for you. Dont forget his words of sorry were words of anger in your eyes. And had you not have had a rear fender that brushed him off and slowed him as he hit your paint your boat would have had a big hole in it Link to comment Share on other sites More sharing options...
Scholar Gypsy Posted August 26, 2016 Report Share Posted August 26, 2016 Dont forget to add how worried you are about boating on a river incase this happens again and your getting sleepless nights over it! Dont forget to mention that he was going as fast as possable and was aiming for you. Dont forget his words of sorry were words of anger in your eyes. And had you not have had a rear fender that brushed him off and slowed him as he hit your paint your boat would have had a big hole in it Whiplash section will require a calculation of the relative momentum of the two boats. Let us say 15 tonnes at 1 mph which is about 0.44 m/sec. Momentum = 7000 kgm/sec. For the sculler shall we say 100 kg ? Even if he was travelling 10 times faster, momentum still only 400 kgm/sec, much less than the narrow boat. So the change in speed of the narrow boat will be very small... Sorry. Link to comment Share on other sites More sharing options...
MtB Posted August 26, 2016 Report Share Posted August 26, 2016 Whiplash section will require a calculation of the relative momentum of the two boats. Let us say 15 tonnes at 1 mph which is about 0.44 m/sec. Momentum = 7000 kgm/sec. For the sculler shall we say 100 kg ? Even if he was travelling 10 times faster, momentum still only 400 kgm/sec, much less than the narrow boat. So the change in speed of the narrow boat will be very small... Sorry. I see you ducked the more complex calcluation required to determine the NB change in velocity! (Which I suspect requires more information given the two masses did not join togeher and continue as a single mass..) Link to comment Share on other sites More sharing options...
Scholar Gypsy Posted August 26, 2016 Report Share Posted August 26, 2016 I see you ducked the more complex calcluation required to determine the NB change in velocity! (Which I suspect requires more information given the two masses did not join togeher and continue as a single mass..) Yes, well assuming the two boats are travelling in the same direction, and stick together, then their joint speed after the collision would increase to 1.059 mph. Interestingly, some 32% of the initial kinetic energy is lost, converted into other forms of energy (eg the noise of splintering woodwork, cursing by those involved etc). The scull in this case has 2/3rds of the energy of the boat (1/2 m v2). Link to comment Share on other sites More sharing options...
TheBiscuits Posted August 26, 2016 Report Share Posted August 26, 2016 Yes, well assuming the two boats are travelling in the same direction, and stick together, then their joint speed after the collision would increase to 1.059 mph. Interestingly, some 32% of the initial kinetic energy is lost, converted into other forms of energy (eg the noise of splintering woodwork, cursing by those involved etc). The scull in this case has 2/3rds of the energy of the boat (1/2 m v2). Depends if it was an African scull or a European scull, and is always proportional to the coconut. 2 Link to comment Share on other sites More sharing options...
MtB Posted August 26, 2016 Report Share Posted August 26, 2016 Interestingly, some 32% of the initial kinetic energy is lost, converted into other forms of energy (eg the noise of splintering woodwork, cursing by those involved etc). The scull in this case has 2/3rds of the energy of the boat (1/2 m v2). Is it? Where does that figure of 32% originate? I'd have thought it would vary widely. Link to comment Share on other sites More sharing options...
Scholar Gypsy Posted August 26, 2016 Report Share Posted August 26, 2016 Is it? Where does that figure of 32% originate? I'd have thought it would vary widely. Yes, it will vary a lot, depending on the ratios of mass and of speed. Using the ratios above - narrow boat weighing 150 times the scull; scull going 10 times faster, then the velocity of the narrowboat increases by about 6% when the scull crashes into it (and sticks to it) the energy of the narrowboat beforehand is 1480, and of the scull 990 (Joules), total 2470 the kinetic energy afterwards is 1670, so 800 of energy is converted to other modes. (32%). Link to comment Share on other sites More sharing options...
MtB Posted August 26, 2016 Report Share Posted August 26, 2016 Yes, it will vary a lot, depending on the ratios of mass and of speed. Using the ratios above - narrow boat weighing 150 times the scull; scull going 10 times faster, then the velocity of the narrowboat increases by about 6% when the scull crashes into it (and sticks to it) the energy of the narrowboat beforehand is 1480, and of the scull 990 (Joules), total 2470 the kinetic energy afterwards is 1670, so 800 of energy is converted to other modes. (32%). Ohh I see. I misunderstood, thinking you meant 32% of the kinetic energy was dissipated in the crushing and snapping of the wood! Link to comment Share on other sites More sharing options...
Theo Posted August 26, 2016 Report Share Posted August 26, 2016 Surely if the oars were alternated then it wasn't sculling. As I remember from the 60s sculling required each person to have 2 oars. Absolutely. I should have read it before hitting send. I will edit is now. Nick Link to comment Share on other sites More sharing options...
Theo Posted August 26, 2016 Report Share Posted August 26, 2016 Whiplash section will require a calculation of the relative momentum of the two boats. Let us say 15 tonnes at 1 mph which is about 0.44 m/sec. Momentum = 7000 kgm/sec. For the sculler shall we say 100 kg ? Even if he was travelling 10 times faster, momentum still only 400 kgm/sec, much less than the narrow boat. So the change in speed of the narrow boat will be very small... Sorry. But sir! But sir!! Please sir, excuse me. Isn't momentum a vector quantity? Shouldn't you be talking about velocity? Do I get a star for knowing that? Link to comment Share on other sites More sharing options...
Scholar Gypsy Posted August 26, 2016 Report Share Posted August 26, 2016 But sir! But sir!! Please sir, excuse me. Isn't momentum a vector quantity? Shouldn't you be talking about velocity? Do I get a star for knowing that? I can't give you a gold star, but I would give you a green one if I had any left today. Sorry, especially as you have just given me one on another thread. You are right, that momentum is a vector, while energy is scalar. However in an earlier post I did say I was assuming the two boats were travelling in the same direction, so I can measure velocity using a single number. Of course those numbers could be both positive (in the case here, of one boat crashing into the other) or one positive and one negative (a head-on collision) -- these two cases would give different results... Link to comment Share on other sites More sharing options...
BGA Posted August 26, 2016 Report Share Posted August 26, 2016 How hard would it be to fit a small mirror so that they can see what is behind them? Steve Or if you are a techy perhaps a helmet cam and monitor. Link to comment Share on other sites More sharing options...
Theo Posted August 26, 2016 Report Share Posted August 26, 2016 I can't give you a gold star, but I would give you a green one if I had any left today. Sorry, especially as you have just given me one on another thread. You are right, that momentum is a vector, while energy is scalar. However in an earlier post I did say I was assuming the two boats were travelling in the same direction, so I can measure velocity using a single number. Of course those numbers could be both positive (in the case here, of one boat crashing into the other) or one positive and one negative (a head-on collision) -- these two cases would give different results... You can't give mods greenies anyway. I suppose it is to prevent corruption. Link to comment Share on other sites More sharing options...
FadeToScarlet Posted August 26, 2016 Report Share Posted August 26, 2016 Ah, a bit of a 'pride' thing then. Anyone using a mirror is a wuss! Not really. They're not that helpful, and do give a false sense of security. Even with a mirror, there's a blind spot, albeit smaller, and when using one the user would be tempted to look around less. It's recommended that Scullers and steerers of coxless boats look around every 3-5 strokes, in alternate directions- unless doing something like racing on a rowing lake, with no other traffic to worry about. Me, I stick to coxing mostly, I prefer to see where I'm going. Link to comment Share on other sites More sharing options...
ditchcrawler Posted August 27, 2016 Report Share Posted August 27, 2016 I nearly had one hit me up the bum on the wide bit of the Nene. He had already passed me going the other way, turned round and came steaming up behind me till I blew the horn Link to comment Share on other sites More sharing options...
Horace42 Posted August 28, 2016 Report Share Posted August 28, 2016 But sir! But sir!! Please sir, excuse me. Isn't momentum a vector quantity? Shouldn't you be talking about velocity? Do I get a star for knowing that? Does the vector v scalar knowledge matter at this basic level of maths (a sincere question based on limited understanding). My simple formula gives the same answer regardless of definition of the quantities. If the definition does matter then my lack of appreciation of this point might explain why I had trouble grasping some important points of advanced engineering science. For instance, would it help explain where the kinetic energy has gone.? Link to comment Share on other sites More sharing options...
Scholar Gypsy Posted August 28, 2016 Report Share Posted August 28, 2016 Does the vector v scalar knowledge matter at this basic level of maths (a sincere question based on limited understanding). My simple formula gives the same answer regardless of definition of the quantities. If the definition does matter then my lack of appreciation of this point might explain why I had trouble grasping some important points of advanced engineering science. For instance, would it help explain where the kinetic energy has gone.? It does matter. In the made up example above, the mass of the narrowboat is 15 times that of the scull, but the scull is travelling 10 times faster before the collision. The two boats are then assumed to form a single object. It does matter whether the initial velocities are both going in the same direction, 180o apart (head on collision), or some other angle in between - this is the vector bit. I chose the first example. Roughly, the scull loses 98.9% of its initial kinetic energy (in essence as its speed reduces by nearly 90%, and 0.1 * 0.1 = 0.01), of this 18.4% is added to the narrowboat which speeds up a small amount, and 80.5% is converted to other forms of energy - crunching wood, a slightly squashed narrowboat (elastic energy), noise, heat, water turbulence etc, Link to comment Share on other sites More sharing options...
Theo Posted August 28, 2016 Report Share Posted August 28, 2016 (edited) It does matter. In the made up example above, the mass of the narrowboat is 15 times that of the scull, but the scull is travelling 10 times faster before the collision. The two boats are then assumed to form a single object. It does matter whether the initial velocities are both going in the same direction, 180o apart (head on collision), or some other angle in between - this is the vector bit. I chose the first example. Roughly, the scull loses 98.9% of its initial kinetic energy (in essence as its speed reduces by nearly 90%, and 0.1 * 0.1 = 0.01), of this 18.4% is added to the narrowboat which speeds up a small amount, and 80.5% is converted to other forms of energy - crunching wood, a slightly squashed narrowboat (elastic energy), noise, heat, water turbulence etc, Here are some figures to illustrate what Scholar Gypsy has said: KE = 1/2 x m x v x v KE is measured in joules m is measured in kg v is measured in m/s In an isolated system where you can consider the narrow boat and all its contents and the scull and all its contents to be unaffected by any forces except those between the two craft, then you can take the momentum before the collision to be equal to the momentum immediately after the collision. P = mv P = momentum in Kg-m/s m = mass in kg. If the scull remains in contact with the narrow boat after the collision rather than bouncing off then, as SG says, they can be considered to be one body with the total mass of nb + scull Using all that lot to work out the final velocity of Halsall and scull: Shall we say that Halsall and all that's in it has a mass of 20T or 20,000kg and the scull and its occupant and oars 200kg (that might well be a bit too much but it might make the sums easier. Halsall was stationary so had no momentum before the collision. The scull might have been moving at 15mph, about 7m/s Momentum before collision = 20,000 x 0 + 200 x 7 = 1,400kg-m/s Momentum after collision is the same so (20,000+200) x final velocity = 1400 final velocity = 1400/(20000+200) = 0.07m/s which is not a lot (0.2mph) If we feed these numbers into the energy formula we get: KE before the collision = 1/2 x 200 x 7x7 = 4900 joules KE after the collision = 1/2 x 20200 x 0.07 x 0.07 = 49.5 joules So using these figures it seems that we have lost 99% of the KE. I just though that some figures might help. N Edited August 28, 2016 by Theo Link to comment Share on other sites More sharing options...
system 4-50 Posted August 28, 2016 Report Share Posted August 28, 2016 So how many rowboats have to hit a narrowboat to heat it up by 1 degree celsius? Link to comment Share on other sites More sharing options...
Scholar Gypsy Posted August 28, 2016 Report Share Posted August 28, 2016 well the specific heat capacity of steel is 420 J per kg per degree C (source). So if by some miracle all the lost kinetic energy went to heat up the boat then each collision would raise the temperature by approx (4850/420)/20,000 degrees, about 1/2000th of a degree. So the answer is about 2,000 collisions. This ignores heat loss into the water of course, and also assumes that all of the mass of the boat is steel, even the fake rivets. 1 Link to comment Share on other sites More sharing options...
X Alan W Posted August 28, 2016 Report Share Posted August 28, 2016 How hard would it be to fit a small mirror so that they can see what is behind them? Steve He doesn't need to see that way (he's facing that way) It's seeing what he's about to run into that he needs the mirror for. Link to comment Share on other sites More sharing options...
Neil Walker Posted August 28, 2016 Report Share Posted August 28, 2016 (edited) Your all nuts, brainy but nuts! Love it! Edit for being nuts! Edited August 28, 2016 by Neil Walker Link to comment Share on other sites More sharing options...
Horace42 Posted August 28, 2016 Report Share Posted August 28, 2016 It does matter. In the made up example above, the mass of the narrowboat is 15 times that of the scull, but the scull is travelling 10 times faster before the collision. The two boats are then assumed to form a single object. It does matter whether the initial velocities are both going in the same direction, 180o apart (head on collision), or some other angle in between - this is the vector bit. I chose the first example. Roughly, the scull loses 98.9% of its initial kinetic energy (in essence as its speed reduces by nearly 90%, and 0.1 * 0.1 = 0.01), of this 18.4% is added to the narrowboat which speeds up a small amount, and 80.5% is converted to other forms of energy - crunching wood, a slightly squashed narrowboat (elastic energy), noise, heat, water turbulence etc, Thanks. I think I follow you. Link to comment Share on other sites More sharing options...
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