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The physics in cycling



 
 
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  #1  
Old February 3rd 11, 07:23 PM posted to aus.bicycle
Geoff Lock[_2_]
external usenet poster
 
Posts: 475
Default 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  
Old February 3rd 11, 11:21 PM posted to aus.bicycle
Moike
external usenet poster
 
Posts: 116
Default 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  
Old February 4th 11, 03:13 AM posted to aus.bicycle
F Murtz[_2_]
external usenet poster
 
Posts: 193
Default 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  
Old February 4th 11, 04:28 AM posted to aus.bicycle
Geoff Lock[_2_]
external usenet poster
 
Posts: 475
Default 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
  #5  
Old February 4th 11, 04:32 AM posted to aus.bicycle
Geoff Lock[_2_]
external usenet poster
 
Posts: 475
Default 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  
Old February 4th 11, 04:54 AM posted to aus.bicycle
Tomasso[_7_]
external usenet poster
 
Posts: 11
Default 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.
  #7  
Old February 4th 11, 05:23 AM posted to aus.bicycle
Geoff Lock[_2_]
external usenet poster
 
Posts: 475
Default 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  
Old February 4th 11, 07:49 AM posted to aus.bicycle
John[_24_]
external usenet poster
 
Posts: 11
Default 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  
Old February 4th 11, 11:56 AM posted to aus.bicycle
Dave Hughes
external usenet poster
 
Posts: 228
Default 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  
Old February 4th 11, 06:32 PM posted to aus.bicycle
Geoff Lock[_2_]
external usenet poster
 
Posts: 475
Default 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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