How does weight actually matter?
12-09-11, 07:05 AM
#51
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I am unable to convince the heavies in my cycling group of this (possibly because I'm wrong) but here goes: being heavier does not make you descend faster. If you are 10% heavier (say) then there is 10% more gravitational force between you and the earth - but the thing is this is *exactly* offset by there being 10% more inertia for this force to overcome. .
There are fifty million demonstrations of this, none of which has overcome the popular misconception. Here is a neat old one: https://video.google.co.uk/videoplay?...91572259784994 - it doesn't work on earth because feathers are frightened of the earth. This is how come birds can fly.
There are fifty million demonstrations of this, none of which has overcome the popular misconception. Here is a neat old one: https://video.google.co.uk/videoplay?...91572259784994 - it doesn't work on earth because feathers are frightened of the earth. This is how come birds can fly.
12-09-11, 08:11 AM
#52
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I am unable to convince the heavies in my cycling group of this (possibly because I'm wrong) but here goes: being heavier does not make you descend faster. If you are 10% heavier (say) then there is 10% more gravitational force between you and the earth - but the thing is this is *exactly* offset by there being 10% more inertia for this force to overcome. .
That would make perfect sense in a vacuum. Feather and a rock would fall at the same speed (in a vacuum). However, in the real world with air drag, heavier rider (all other things being equal - road, bike etc) will descend faster, because extra weight is not negated with (that much) extra wind drag.
Logic behind this is: at downhill speeds wind drag is a lot more significant resistance to overcome than inertia.
12-09-11, 08:23 AM
#53
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12-09-11, 10:42 AM
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I am unable to convince the heavies in my cycling group of this (possibly because I'm wrong) but here goes: being heavier does not make you descend faster. If you are 10% heavier (say) then there is 10% more gravitational force between you and the earth - but the thing is this is *exactly* offset by there being 10% more inertia for this force to overcome.
When you make bigger people frontal area (Sd) increases with the square of height while mass goes up with its cube. With more force pulling them down-hill and a lesser drag increase at a given speed big people have a higher terminal velocity where drag (mostly aerodynamic, increasing with the square of velocity) equals the component of their weight vector parallel to the incline.
When you add flab to the same person you can increase weight with no drag increase.
From personal experience:
A 145 pound 5'10" climber is slower down the same grade than a 200 pound rider.
A 110 pound female skydiver in the classic frog-man position who isn't wearing a skin tight jumpsuit and arching her back like a yogi (or wearing weights) might fall 105 MPH while a 250 pound guy who's nickname starts with "Big" will go 145 MPH and be considered an anvil unless he wears a baggy clown suit and perhaps wings. This makes coed naked skydiving more difficult than you'd think.
Inertia is only a factor during acceleration (including deceleration).
Last edited by Drew Eckhardt; 12-09-11 at 10:50 AM.
12-09-11, 10:55 AM
#55
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I am unable to convince the heavies in my cycling group of this (possibly because I'm wrong) but here goes: being heavier does not make you descend faster. If you are 10% heavier (say) then there is 10% more gravitational force between you and the earth - but the thing is this is *exactly* offset by there being 10% more inertia for this force to overcome. .
There are fifty million demonstrations of this, none of which has overcome the popular misconception. Here is a neat old one: https://video.google.co.uk/videoplay?...91572259784994 - it doesn't work on earth because feathers are frightened of the earth. This is how come birds can fly.
There are fifty million demonstrations of this, none of which has overcome the popular misconception. Here is a neat old one: https://video.google.co.uk/videoplay?...91572259784994 - it doesn't work on earth because feathers are frightened of the earth. This is how come birds can fly.
12-09-11, 10:56 AM
#56
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Which is why tandems are so blazingly fast downhill... the weight of two people with the frontal area of one.
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12-09-11, 10:58 AM
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A lighter rider- assuming similar skills and bike to a heavier rider- can brake later going into corners. No small feature, this!
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