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#1
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The physics in cycling
OK, please bear with me as I lead up to how I got onto my torts on
physics in cycling. I have just walked in and I am still sweating after riding the 14kms back to my place via my usual slightly longer route and it has taken me 34mins, which is about average over the 3-odd years that I have been riding that piece of tarmac. So what, I hear you say? Well, this arvo, on the way to the Eastern Suburbs, I found some canvas which someone had tossed out during one of those garbage days. This is not just any bit of canvas but seems to be something for a small truck/trailer/ute. It has eyelets and ropes and good stitching so I am assuming there is a rip somewhere, but I dunno cos it is all neatly folded up in a bundle weighing about 8kgs and I have not opened and spread the whole thing out yet. Anyway, I decided I wanted this bit of road find (I am using the "definition" at this link - http://www.sheldonbrown.com/eagle.html), so I lashed this bundle of canvas (approx dimensions 30cm x 20cm x 45cm unlashed) to my backpack using a bit of rope which I always carry around with me in my backpack - bits of rope are often very useful, I find. So, I am now carrying an extra 8kgs - never mind what the total weight of backpack and bundle of canvas is (it's 12kgs if you must know - I weighed it using some electronic scales I have access to at this place I know - ok ok ok 11.8kgs, for crying out loud!!! One decimal place is all I am gonna give yer, alright???). Now, I would have tort that carrying the extra weight (and yes, it pulled a bit harder on the shoulder straps of my backpack) would mean pedalling my bike would be more difficult and becos I am not that strong, my time for the 14kms would be around the 40-45min mark. You can imagine my surprise when I clocked 34mins! As the good Professor would say, "Why is this so?" Here's my guess. Once I have overcome the starting friction from the additional weight, my rolling momentum ...... eeerrr... keeps me rolling. Therefore, the additional effort required is not really that much more. Also, some of the slight downhill inclines along my route generate faster (ok ok ok slightly faster?) speeds due to the additional weight I am carrying. In the uphill sections, I do feel the additional effort (a bit) if I remain seated but I would "stand" on the pedals and drive down with my hips whilst trying to balance the backpack in line with the downward direction of my driving action. In other words, trying to use the weight of the backpack to increase my downward force on the pedals, hopefully making up for the additional load I am carrying (well, that was my rationale and I have no idea why I tort it should work other than simple physics). I dunno if I am making sense here. Maybe there are others here in this newsgroup with a better understanding of cycling AND physics who might offer a better explanation cos I am kinda fresh out of explanations and I am still trying to satisfy myself why I have done a bog standard average time when I should not have. PS - No changes to bike (the Cannondale). Bike was as it was from Monday. PSS - No changes to my physical self other than my normal diet on a normal Thursday unless you wanna count the bacon and eggs I had as dinner I have bacon and eggs and toast regularly for dinner (with a salad+fetta+olives). |
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#2
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The physics in cycling
Geoff Lock wrote:
OK, please bear with me as I lead up to how I got onto my torts on physics in cycling. I have just walked in and I am still sweating after riding the 14kms back to my place via my usual slightly longer route and it has taken me 34mins, which is about average over the 3-odd years that I have been riding that piece of tarmac. So what, I hear you say? Well, this arvo, on the way to the Eastern Suburbs, I found some canvas which someone had tossed out during one of those garbage days. This is not just any bit of canvas but seems to be something for a small truck/trailer/ute. It has eyelets and ropes and good stitching so I am assuming there is a rip somewhere, but I dunno cos it is all neatly folded up in a bundle weighing about 8kgs and I have not opened and spread the whole thing out yet. Anyway, I decided I wanted this bit of road find (I am using the "definition" at this link - http://www.sheldonbrown.com/eagle.html), so I lashed this bundle of canvas (approx dimensions 30cm x 20cm x 45cm unlashed) to my backpack using a bit of rope which I always carry around with me in my backpack - bits of rope are often very useful, I find. So, I am now carrying an extra 8kgs - never mind what the total weight of backpack and bundle of canvas is (it's 12kgs if you must know - I weighed it using some electronic scales I have access to at this place I know - ok ok ok 11.8kgs, for crying out loud!!! One decimal place is all I am gonna give yer, alright???). Now, I would have tort that carrying the extra weight (and yes, it pulled a bit harder on the shoulder straps of my backpack) would mean pedalling my bike would be more difficult and becos I am not that strong, my time for the 14kms would be around the 40-45min mark. You can imagine my surprise when I clocked 34mins! As the good Professor would say, "Why is this so?" Here's my guess. Once I have overcome the starting friction from the additional weight, my rolling momentum ...... eeerrr... keeps me rolling. Therefore, the additional effort required is not really that much more. Also, some of the slight downhill inclines along my route generate faster (ok ok ok slightly faster?) speeds due to the additional weight I am carrying. In the uphill sections, I do feel the additional effort (a bit) if I remain seated but I would "stand" on the pedals and drive down with my hips whilst trying to balance the backpack in line with the downward direction of my driving action. In other words, trying to use the weight of the backpack to increase my downward force on the pedals, hopefully making up for the additional load I am carrying (well, that was my rationale and I have no idea why I tort it should work other than simple physics). I dunno if I am making sense here. Maybe there are others here in this newsgroup with a better understanding of cycling AND physics who might offer a better explanation cos I am kinda fresh out of explanations and I am still trying to satisfy myself why I have done a bog standard average time when I should not have. PS - No changes to bike (the Cannondale). Bike was as it was from Monday. PSS - No changes to my physical self other than my normal diet on a normal Thursday unless you wanna count the bacon and eggs I had as dinner I have bacon and eggs and toast regularly for dinner (with a salad+fetta+olives). Disclaimer.... I am a Physics teacher, (or will be in a couple of days) but cycling is not on the VCE Physics curriculum You are right about cycling on the flat. The additional mass means you need to exert additional force to overcome inertia and accelerate from rest, but (assuming it doesn't affect your wind resistance) once up to speed it should make no difference. When coasting and slowing down the slight increase in kinetic energy due to the increased mass should see you roll a little further. There would be lottle or no downhill effect, since the additional force of gravity on your increased mass would be accounted for by the additional force needed to accelerate the mass. (there would be a very small increase in speed due to the fact hat while all the other forces are greater, wind resistance is unchanged.) On uphill sections, the additional weight means you need to exert greater force to climb the hill. As you point out, the additional weight allows you to exert a higher down force on the pedals, but you still need to use more energy to climb the hill. So yes, overall you should be slower, depending on how many hills you climb, but perhaps your awareness of the extra load made you work a little harder. Moike |
#3
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The physics in cycling
Geoff Lock wrote:
OK, please bear with me as I lead up to how I got onto my torts on physics in cycling. I have just walked in and I am still sweating after riding the 14kms back to my place via my usual slightly longer route and it has taken me 34mins, which is about average over the 3-odd years that I have been riding that piece of tarmac. So what, I hear you say? Well, this arvo, on the way to the Eastern Suburbs, I found some canvas which someone had tossed out during one of those garbage days. This is not just any bit of canvas but seems to be something for a small truck/trailer/ute. It has eyelets and ropes and good stitching so I am assuming there is a rip somewhere, but I dunno cos it is all neatly folded up in a bundle weighing about 8kgs and I have not opened and spread the whole thing out yet. Anyway, I decided I wanted this bit of road find (I am using the "definition" at this link - http://www.sheldonbrown.com/eagle.html), so I lashed this bundle of canvas (approx dimensions 30cm x 20cm x 45cm unlashed) to my backpack using a bit of rope which I always carry around with me in my backpack - bits of rope are often very useful, I find. So, I am now carrying an extra 8kgs - never mind what the total weight of backpack and bundle of canvas is (it's 12kgs if you must know - I weighed it using some electronic scales I have access to at this place I know - ok ok ok 11.8kgs, for crying out loud!!! One decimal place is all I am gonna give yer, alright???). Now, I would have tort that carrying the extra weight (and yes, it pulled a bit harder on the shoulder straps of my backpack) would mean pedalling my bike would be more difficult and becos I am not that strong, my time for the 14kms would be around the 40-45min mark. You can imagine my surprise when I clocked 34mins! As the good Professor would say, "Why is this so?" Here's my guess. Once I have overcome the starting friction from the additional weight, my rolling momentum ...... eeerrr... keeps me rolling. Therefore, the additional effort required is not really that much more. Also, some of the slight downhill inclines along my route generate faster (ok ok ok slightly faster?) speeds due to the additional weight I am carrying. In the uphill sections, I do feel the additional effort (a bit) if I remain seated but I would "stand" on the pedals and drive down with my hips whilst trying to balance the backpack in line with the downward direction of my driving action. In other words, trying to use the weight of the backpack to increase my downward force on the pedals, hopefully making up for the additional load I am carrying (well, that was my rationale and I have no idea why I tort it should work other than simple physics). I dunno if I am making sense here. Maybe there are others here in this newsgroup with a better understanding of cycling AND physics who might offer a better explanation cos I am kinda fresh out of explanations and I am still trying to satisfy myself why I have done a bog standard average time when I should not have. PS - No changes to bike (the Cannondale). Bike was as it was from Monday. PSS - No changes to my physical self other than my normal diet on a normal Thursday unless you wanna count the bacon and eggs I had as dinner I have bacon and eggs and toast regularly for dinner (with a salad+fetta+olives). Yes,but did the canvas have a rip in it? |
#4
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The physics in cycling
On 4/02/2011 9:21 AM, Moike wrote:
Geoff Lock wrote: OK, please bear with me as I lead up to how I got onto my torts on physics in cycling. Disclaimer.... I am a Physics teacher, (or will be in a couple of days) but cycling is not on the VCE Physics curriculum Heheheh!! I can almost see future Victorian students taking up cycling and they don't know why )) You are right about cycling on the flat. The additional mass means you need to exert additional force to overcome inertia and accelerate from rest, but (assuming it doesn't affect your wind resistance) once up to speed it should make no difference. When coasting and slowing down the slight increase in kinetic energy due to the increased mass should see you roll a little further. Hm, ok, that is kind of verifying my torts about my rolling momentum. There would be lottle or no downhill effect, since the additional force of gravity on your increased mass would be accounted for by the additional force needed to accelerate the mass. (there would be a very small increase in speed due to the fact hat while all the other forces are greater, wind resistance is unchanged.) I didn't have that many downhill sections but the couple I had seemed to feel easier but I am guessing it may be simply psychological. On uphill sections, the additional weight means you need to exert greater force to climb the hill. As you point out, the additional weight allows you to exert a higher down force on the pedals, but you still need to use more energy to climb the hill. It didn't seem to feel like I need to use a lot more energy than I expected. Changing my riding style from seated to standing did seem to increase power. So yes, overall you should be slower, depending on how many hills you climb, but perhaps your awareness of the extra load made you work a little harder. Dunno. Maybe you are right in that I was working a bit harder without realising it. The brain is a weird thing - or maybe it's just me that's weird and not me brain Also, maybe the slight increase of 8kgs is not enough to stress my body to the stage where degradation in performance is noticeable. So instead of matters of physics, I should be talking about physiology(?). For example, how would my body react if I loaded it up with an additional 80kgs (assuming I could, somehow, carry 80kgs snugly lashed on). Damn, I wish there was a device which could measure the exact amt of energy I burn given exact loads, frictional forces, wind, blah blah blah Of cos, I would expect to pay no more than $35 off Ebay |
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The physics in cycling
On 4/02/2011 1:13 PM, F Murtz wrote:
Geoff Lock wrote: Well, this arvo, on the way to the Eastern Suburbs, I found some canvas which someone had tossed out during one of those garbage days. This is not just any bit of canvas but seems to be something for a small truck/trailer/ute. It has eyelets and ropes and good stitching so I am assuming there is a rip somewhere, but I dunno cos it is all neatly folded up in a bundle weighing about 8kgs and I have not opened and spread the whole thing out yet. Yes,but did the canvas have a rip in it? Dunno yet. I live in very cramped quarters and it would be difficult to spread it all out right now. I am saving the big surprise for the weekend when I can re-organise things around so I can have a bit more room. |
#6
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The physics in cycling
"... PS - No changes to bike (the Cannondale). Bike was as it was from Monday. How old is the Cannondale? Your "spare" bike. And what was the mention of the Scott? T. |
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The physics in cycling
On 4/02/2011 2:54 PM, Tomasso wrote:
"... PS - No changes to bike (the Cannondale). Bike was as it was from Monday. How old is the Cannondale? Your "spare" bike. The Cannondale is probably based on a 20 year-old design. It is about 10kgs compared to about 15kgs for my normal road bike. It actually belongs to the daughter but she is cool with Dad using it. She paid $180 for it off Ebay. And what was the mention of the Scott? The Scott is my good bike which is ridden once a year for the MS Gong Ride. The daughter rode it this year while I rode my normal piece of crap. The Scott is one of the 2008 models in the Speedster Series - flat bar setup. I got it in mid 2009 from a bloke who had it sitting in his garage for months and months and months. I helped him out in a few things and he sold the bike to me for $500!!! He rode it twice - once around Hunters Hill where he lives and a second time to the City. |
#8
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The physics in cycling
On 2011-02-03, Geoff Lock glock@home wrote:
OK, please bear with me as I lead up to how I got onto my torts on physics in cycling... According to this article http://www.bmj.com/content/341/bmj.c6801 the mass of the bike makes negligible difference to the journey time. The article is a little tongue-in-cheek, but the author seems to have conducted his study very diligently. Full article is he http://www.bmj.com/content/341/bmj.c6801.full.pdf -- John Any plan where you lose your hat is a bad plan. - Jagermonster, girlgenius.com |
#9
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The physics in cycling
Dunno. Maybe you are right in that I was working a bit harder without realising it. The brain is a weird thing - or maybe it's just me that's weird and not me brain I found today's ride a touch easier than the rest of the week's because the breeze cooled thigns down a touch. That'll help you ride home. Other than that, momentum on the flat is increased due to increased mass, but once you're up to speed it'll be the same effort to stay there. The extra mass will help a bit over lumps and bumps, but uphills will hurt more. The extra incentive to push (out of the saddle) will drop the time a touch, so it's not that surprising. The other way of looking at it: 12kg is going to be roughly 10% of your total bike and body weight (assuming you're not either annoyingly light or disturbingly heavy, and giving a reasonably leeway in "roughly). On the flat it'll make virtually no difference, uphill it'll add 10% to your time, downhill it'll drop about 8% from your time. The overall effect is bugger all, but you'll certainly notice it being heavier. Oh, and Moike - you should do OK at Physics, mail me if you ever need a hand! -- Dave Hughes - "Love is a snowmobile racing across the tundra and then suddenly it flips over, pinning you underneath. At night, the ice weasels come." - Matt Groening |
#10
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The physics in cycling
On 4/02/2011 9:56 PM, Dave Hughes wrote:
Dunno. Maybe you are right in that I was working a bit harder without realising it. The brain is a weird thing - or maybe it's just me that's weird and not me brain I found today's ride a touch easier than the rest of the week's because the breeze cooled thigns down a touch. That'll help you ride home. Other than that, momentum on the flat is increased due to increased mass, but once you're up to speed it'll be the same effort to stay there. The extra mass will help a bit over lumps and bumps, but uphills will hurt more. True, true - the lumps and bumps did seem a bit easier. The bike did kinda feel a bit more wobbly which I put to the extra weight changing my centre of gravity. The extra incentive to push (out of the saddle) will drop the time a touch, so it's not that surprising. I did feel a bit more effort but not that much more. I put that towards the technique I was using - ie driving down using my hips whilst directing the weight of my backpack down thru my hips. The other way of looking at it: 12kg is going to be roughly 10% of your total bike and body weight (assuming you're not either annoyingly light or disturbingly heavy, and giving a reasonably leeway in "roughly). On the flat it'll make virtually no difference, uphill it'll add 10% to your time, downhill it'll drop about 8% from your time. The overall effect is bugger all, but you'll certainly notice it being heavier. I think I have been barking up the wrong tree here when I saw it as a matter of physics. It seems that becos the majority of my ride is relatively flat, the additional weight counts for very little - as I kinda suspected but could not figure out with seeking more advice on physics. The uphill section towards the end of my ride, although a bit more difficult due to the additional 8kg weight, is most probably offset by me working harder on the pedals (with some contribution from load balancing) and I didn't notice it becos there was not really that much additional weight anyway. Things would most probably be very very different if I was loaded up with an 80kg load which I have no intention of doing anytime soon Oh, and Moike - you should do OK at Physics, mail me if you ever need a hand! Yeah, Moike did alright in straightening me out. He also gave me the clue that physiology, rather than just physics alone, may be involved as well. Bloody obvious, really - I knew it all the time - as soon as someone points it out of cos |
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