Trail damage/shock absorbers/suspension



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Mike Vandeman wrote:

>On Mon, 07 Apr 2003 21:03:56 -0400, PeterH <[email protected]> wrote:
>
>.Mike Vandeman wrote: . .> .>Your inability to understand even "DUH" puts you in a class by
>yourself. .>Special, as in "Special Olympics". .> .> .> .> .My understanding of such poor usage is
>quite complete. And your ad .hominem tactics seriously erode any chance of credibility. I suggest
>you .refine your techniques after consulting the list of logical fallacies .which is neatly
>presented here: . .http://www.datanation.com/fallacies/index.htm . .Since you are known to violate
>a goodly number of them, you might just .gain a thing or two by becoming familiar with the rules
>you flout so .flamboyantly.
>
>As usual, you claim something vague. If you had to be SPECIFIC about what I said wrong, it would be
>obvious that you are full of it.
>
>
>
>
I rest my case.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
Mike Vandeman wrote:

>On Tue, 08 Apr 2003 19:00:14 -0400, PeterH <[email protected]> wrote:
>
>.Terri Alvillar wrote: . .>I think Pete H has just violated the monster ego ordinance. Did you mean
>semantics? .>Terri Alvillar .> .> .My monster's ego is quite modest. He has bitten only three
>Seventh Day .Adventists and one Democrat in the last year.
>
>Did you say something?
>
>
>
>
You'll likely never know.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
"Terri Alvillar" <[email protected]> wrote in message
news:[email protected]...
> "Jeff Strickland" <[email protected]> wrote in message
news:<[email protected]>...
> > "Mike Vandeman" <[email protected]> wrote in message
> > news:[email protected]...
> > > On 3 Apr 2003 21:30:56 -0800, [email protected] (Terri Alvillar) wrote:
> > >
> > > .I wonder if any studies have been done to correlate mountain bike .equipment shock absorbers
> > > and suspension with damage to terrain? Is .the damage to terrain commensurate with the level
> > > of shock absorbing .technology on the vehicle?
> > >
> > > Yes. By Newton's laws of physics, every action has an equal and
opposite
> > > reaction. In other words, the force applied to the ground (or anything
> > else in
> > > their path, such as a plant, animal, or person) is identical to the
force
> > > applied to the bike. The reason that mountain bikes are built much
> > stronger than
> > > normal bikes is that they encounter much greater FORCES. Therefore,
they
> > apply
> > > much greater forces to the ground & everything else in their path. QED
> >
> > Technically, a mountain bike with a shock absorber should have less of
an
> > impact than one without a shock absorber. Think of the words being used here, SHOCK ABSORBER. A
> > shock absorber absorbs shocks, therefore by definition, less of an impact.
> >
> > Think of the water barrels they (CalTrans or others) place on the impact-side of a sign or post.
> > The sign or post might weigh more, but
the
> > impact upon objects that strike the sign or post is lessened. In the
world
> > of bikes and dirt, the dirt is the object that constantly stirkes the
bike
> > (trying to keep the analogy straight), or in other words, the impact of
the
> > bike striking the ground repeatedly is lessened because of the shock absorber. Newton's Law does
> > not take into account the affects of
external
> > forces, such as a shock absorber.
>
>
> So it seems the greater shock absorbing system on a mountain bike, the greater damage is possible
> because one can travel at greater speeds and displace more surface material when braking,
> skidding, and accelerating. Terri Alvillar
> http://homepage.mac.com/terrialvillar/mountainbikedamage/PhotoAlbum11.html

<laugh> Sorry, Terri but I am surprised that you have come to that conclusion after wading through
all these physics arguments. It's a generally accepted fact that because of the weight penalty and
less efficient energy transfer that full suspension mtb bikes are actually slower. More comfortable,
but slower. If you are looking for another arrow for your anti-mountainbiking quiver, you won't find
it using the "suspension is worse" theory. Using that theory would just be embarrassing. You are
correct when you say that skidding displaces surface material but braking and accelerating by
themselves don't displace material to any significant degree. In that respect, it doesn't matter
whether or not you have suspension. It's a shame that you appear to have had a preconcieved idea
when you asked the question.
--
Westie
 
"Mike Vandeman" <[email protected]> wrote in message
news:[email protected]...
> On 8 Apr 2003 08:58:18 -0700, [email protected] (Terri Alvillar) wrote:
>
> ."Jeff Strickland" <[email protected]> wrote in message
news:<[email protected]>...
> .> "Mike Vandeman" <[email protected]> wrote in message .>
> news:[email protected]... .> > On 3 Apr 2003 21:30:56 -0800,
> [email protected] (Terri Alvillar)
wrote:
> .> > .> > .I wonder if any studies have been done to correlate mountain bike .> > .equipment shock
> absorbers and suspension with damage to terrain? Is .> > .the damage to terrain commensurate with
> the level of shock absorbing .> > .technology on the vehicle? .> > .> > Yes. By Newton's laws of
> physics, every action has an equal and
opposite
> .> > reaction. In other words, the force applied to the ground (or
anything
> .> else in .> > their path, such as a plant, animal, or person) is identical to the
force
> .> > applied to the bike. The reason that mountain bikes are built much .> stronger than .> >
> normal bikes is that they encounter much greater FORCES. Therefore,
they
> .> apply .> > much greater forces to the ground & everything else in their path.
QED
> .> .> Technically, a mountain bike with a shock absorber should have less of
an
> .> impact than one without a shock absorber. Think of the words being used .> here, SHOCK
> ABSORBER. A shock absorber absorbs shocks, therefore by .> definition, less of an impact. .> .>
> Think of the water barrels they (CalTrans or others) place on the .> impact-side of a sign or
> post. The sign or post might weigh more, but
the
> .> impact upon objects that strike the sign or post is lessened. In the
world
> .> of bikes and dirt, the dirt is the object that constantly stirkes the
bike
> .> (trying to keep the analogy straight), or in other words, the impact of
the
> .> bike striking the ground repeatedly is lessened because of the shock .> absorber. Newton's Law
> does not take into account the affects of
external
> .> forces, such as a shock absorber. . . .So it seems the greater shock absorbing system on a
> mountain bike, the .greater damage is possible because one can travel at greater speeds .and
> displace more surface material when braking, skidding, and .accelerating.
>
> You go to the head of the class -- for what it's worth. :)
>

********.
 
"Mike Vandeman" <[email protected]> wrote in message
news:[email protected]...
> On Mon, 7 Apr 2003 12:46:07 -0700, "Jeff Strickland" <[email protected]>
wrote:
>
> . ."Mike Vandeman" <[email protected]> wrote in message
> .news:[email protected]... .> On Fri, 4 Apr 2003 14:43:05 -0800, "Jeff
> Strickland" <[email protected]> .wrote: .> .> ."Mike Vandeman" <[email protected]> wrote in
> message .> .news:[email protected]... .> .> On 3 Apr 2003 21:30:56 -0800,
> [email protected] (Terri Alvillar)
wrote:
> .> .> .> .> .I wonder if any studies have been done to correlate mountain bike .> .> .equipment
> shock absorbers and suspension with damage to terrain?
Is
> .> .> .the damage to terrain commensurate with the level of shock
absorbing
> .> .> .technology on the vehicle? .> .> .> .> Yes. By Newton's laws of physics, every action has
> an equal and .opposite .> .> reaction. In other words, the force applied to the ground (or
anything
> .> .else in .> .> their path, such as a plant, animal, or person) is identical to the .force .> .>
> applied to the bike. The reason that mountain bikes are built much .> .stronger than .> .> normal
> bikes is that they encounter much greater FORCES. Therefore, .they .> .apply .> .> much greater
> forces to the ground & everything else in their path.
QED
> .> . .> .Technically, a mountain bike with a shock absorber should have less of
an
> .> .impact than one without a shock absorber. Think of the words being
used
> .> .here, SHOCK ABSORBER. A shock absorber absorbs shocks, therefore by .> .definition, less of an
> impact. .> . .> .Think of the water barrels they (CalTrans or others) place on the .> .impact-side
> of a sign or post. The sign or post might weigh more, but
the
> .> .impact upon objects that strike the sign or post is lessened. In the .world .> .of bikes and
> dirt, the dirt is the object that constantly stirkes the .bike .> .(trying to keep the analogy
> straight), or in other words, the impact
of
> .the .> .bike striking the ground repeatedly is lessened because of the shock .> .absorber.
> Newton's Law does not take into account the affects of
external
> .> .forces, such as a shock absorber. .> .> Oh sure. Newton's laws don't apply to mountain bikes.
> That is the
funniest
> .thing .> I have heard in a long time! Idiot. . .I never said Newton's laws don't apply, what I
> said is that the
simplistic
> .application of them omits the affect of the shock absorber.
>
> But you don't know what that effect is. For example, standing still, the suspension is nothing but
> ADDED DEAD WEIGHT.

But standing still is nothing, it is simply standing still; this is no different than a hiker at
rest. You said that the shock absorber adds shock to the ground because it is heavy, the fact is
that shocks are not that much heavier than the solid parts they replace, and because they acutally
absorb shocks, then the impact on the ground is lessened.
 
"Mike Vandeman" <[email protected]> wrote in message
news:[email protected]...
> On Tue, 8 Apr 2003 15:25:29 -0700, "Jeff Strickland" <[email protected]>
wrote:
>
> . ."Terri Alvillar" <[email protected]> wrote in message
> .news:[email protected]... .> "Jeff Strickland" <[email protected]>
> wrote in message .news:<[email protected]>... .> > "Mike Vandeman"
> <[email protected]> wrote in message .> > news:[email protected]... .>
> > > On 3 Apr 2003 21:30:56 -0800, [email protected] (Terri Alvillar)
wrote:
> .> > > .> > > .I wonder if any studies have been done to correlate mountain bike .> > > .equipment
> shock absorbers and suspension with damage to terrain?
Is
> .> > > .the damage to terrain commensurate with the level of shock
absorbing
> .> > > .technology on the vehicle? .> > > .> > > Yes. By Newton's laws of physics, every action
> has an equal and .opposite .> > > reaction. In other words, the force applied to the ground (or
anything
> .> > else in .> > > their path, such as a plant, animal, or person) is identical to the .force .>
> > > applied to the bike. The reason that mountain bikes are built much .> > stronger than .> > >
> normal bikes is that they encounter much greater FORCES. Therefore, .they .> > apply .> > > much
> greater forces to the ground & everything else in their path.
QED
> .> > .> > Technically, a mountain bike with a shock absorber should have less
of
> .an .> > impact than one without a shock absorber. Think of the words being
used
> .> > here, SHOCK ABSORBER. A shock absorber absorbs shocks, therefore by .> > definition, less of
> an impact. .> > .> > Think of the water barrels they (CalTrans or others) place on the .> >
> impact-side of a sign or post. The sign or post might weigh more, but .the .> > impact upon
> objects that strike the sign or post is lessened. In the .world .> > of bikes and dirt, the dirt
> is the object that constantly stirkes the .bike .> > (trying to keep the analogy straight), or in
> other words, the impact
of
> .the .> > bike striking the ground repeatedly is lessened because of the shock .> > absorber.
> Newton's Law does not take into account the affects of .external .> > forces, such as a shock
> absorber. .> .> .> So it seems the greater shock absorbing system on a mountain bike, the .>
> greater damage is possible because one can travel at greater speeds .> and displace more surface
> material when braking, skidding, and .> accelerating. . .Technically, a bike with greater shock
> absorbing ability will do less .damage. Consider the facts, if you dare. A bike is a moving
> object, and
the
> .impact each time it touches anything is either directed at the point of .impact if no shock
> absorbsion system, or is spread across a wide area if .there is a shock absorbsion system. If a
> tire is impacting the ground,
and
> .there is a shock, then the impact is very slight at the point of impact,
and
> .is gradually spread over a wide area. Try as hard as a rider might, a
shock
> .will lessen the burden of impact, that is the whole point of having one.
>
> Pure hogwash. If a suspension bike is standing still, it already has
greater
> impact, because it is heavier. So it also has greater impact when ridden.
Which
> would you rather get hit by -- a regular, or suspension bike? Obviously,
the
> former, which is much LIGHTER! DUH!

Why are we discussing the impact of a bike that is not even moving? A bike that is not moving, by
definition has no impact. Impact is the result of a moving object colliding with a non-moving, of
moving slower, or moving in the opposite direction. In the case of a bike and the environment, the
impact is the moving bike against the earth or other non-moving object. As for what I prefer to be
hit by, I have never given it much thought, but I suppose that if I was hit by a bike that was
moving at 25mph, I wouldn't care very much either way if the bike has a suspension, or not.

One can not make the leap -- I can't make the leap, but apparently you can -- from suspension
components, or the lack of them, to weight. Many high end bikes with suspensions weigh less than a
cheaper bike without suspension.
 
Mike Vandeman wrote:

>. But bikers cause a lot MORE damage.
>
>
>
More than whom? Where are the data? Give data from reliable sources. Alla time yell, yell, yell, but
there's no data. There can be no useful inquiry into the situation without data & you thus far have
offered none.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
Mike Vandeman wrote:

>On 7 Apr 2003 06:44:38 -0700, [email protected] (Corvus Corvax) wrote: There is no total
>amount of force that has to ."land" on the trail. Energy _is_ conserved.
>
Are you ready for this? (I suspect not.)

>With a suspension, some of .the energy that would have gone into trail erosion or the rider's
>.brakes ends up dissipated as heat by the damping in the suspension.
>
He IS right, you know. Friction among parts of the system is a great energy sink.

>
>That has NOTHING to do with the force on the ground. The force of gravity is greater
>
This would come as a great surprise to Newton; his physics required that the force of gravity
remain constant.

>(because the suspension adds weight).
>
You mean mass. By itself, greater mass is meaningless; it must be coupled with angular momentum
before there's anything going on.

> The horizontal force is greater, because the suspension lets the rider more comfortably
>
A while ago, you were tearing the rider's nuts off. Even, apparently, the female riders.

>ride faster.
>
This is an unsupported generality

>And the greater weight gives the bike more momentum
>
Weight (you mean mass) is one component, angular momentum is another. The combination of the two
produces an action.

>(and hence more force).
>
>.Nonetheless, dry ground can withstand enormous forces without damage. .The more relevant factor is
>the rate of erosion, which has more to do .with friction than force. Skidding is bad. Riding is
>hunky-dory.
>
>Skidding is caused by horizontal force,
>
It's caused by horizontal acceleration.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
Mike Vandeman wrote:

>.No need to swear. .You are correct. The bike DOES hit with full force. But, as I explained, .the
>impact is spread across a wider area and period of time with suspension. .As others have also said,
>the total force remains the same but the force on .any particular piece of trail is less.
>
>So the force of gravity is less in some places?
>
Not what he said at all. Westie never mentioned gravity nor needed to.

F(orce) equals the product of M(ass) and A(cceleration). Had you fogotten? There's no gravity in
that equation.

>I got straight As in Honors Physics from the greatest University in the world (especially in
>physics) -- U.C. Berkeley.
>
As opinionated a statement as has appeared in these threads for quite some time. As I suggested, it
indicates that you passed the courses, not that you necessarily learned anything.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
Mike Vandeman wrote:

>On Mon, 07 Apr 2003 05:48:33 -0400, PeterH <[email protected]> wrote:
>
>.So! It might appear that the manner in which the bike is ridden is, .after all, a variable. That's
>something dozens of posters have tried to .get across to you.
>
>Right. And suspension bikes allow the rider to go faster,
>
And just how do you compute this particular generality? And, even given the "allow," it's
problematic whether there's any coercion to do so.

> hence hit the trail
> with greater force.
>
This need not follow, even if your above generality should prove to be the case.

> DUH!
>
>
>
Again with the juvenile idiom.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
Mike Vandeman wrote:

>On Tue, 8 Apr 2003 11:57:08 +0100, "Shaun Rimmer" <[email protected]> wrote:
>
>
>. .They take in the sudden shock quickly, and apply it back slowly,
>
>That defies the laws of physics. Both are equal.
>
Then designers of shock absorbers have the best kept secret: how to evade the laws of physics. Were
they able to do so, I think they'd be running about applying this mysterious new talent to all sorts
of economically rewarding situations.

>
>It adds greater weight, hence greater force on the ground (vertically & horizontally, since they
>are also ridden faster).
>
And, again, you're trying to equate speed with mass. They are independent variables. Or are you
still forgetting F=MA? From your remark, a heavier bike must of necessity be ridden faster? Totally
insupportable. Conjecture at its height.

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
>That defies the laws of physics. Both are equal.
>
...
>
>It adds greater weight, hence greater force on the ground (vertically & horizontally, since they
>are also ridden faster).
>

Hmmm, this thread does bring a smile to my face. I'm can't recall where Mr Vandeman's got his
physics qualification, somewhere well respected I assume, but I seemed to have taken in more from my
Tertiary course here in the UK (aged 16-17).

OK - this is how a shock absorber works.

A bike travelling forward hits a bump with the front wheel.

On a non-suspended bike, the whole force of that contact is transferred through the tyre (which has
a slight damping effect, but for the sake of argument, lets assume you are running wooden wheels!),
forks, and riders arms, and indeed there is an equal and opposite force transferred into the ground.
(The ground it attempting to lift the entire weight of rider+bike)

Now, on a suspended fork, the force of the contact is actually transferred into a deforming force
of the spring initially, and then is partially disappated as heat, the compression of a gas, and
sound in the shock 'absorbing' parts of the fork. Only a portion of the force is returned to the
ground. (Now, I know not all forks have springs, sometimes its air, or elastomer, but the effect
is the same)

Effectively, the rider+frame are treated as a seperate body to the wheel+fork. They are both
travelling forward with the same speed, and when a bump is contacted, the wheel and fork obtain a
vertical accelleration which is protected from the rider. The rider and frame still only have the
forward motion. (or actually a tiny downward motion with gravity, but ironically enough - the faster
the rider is going, and the better the shock absorbing technology, the less that force will be !)

Use this as an analogy. You are standing still holding a spring which is 50% compressed by the
weight of a bowling ball on top. In the other hand you have a stick with a bowling ball on top. If
you quickly jerk upwards with the stick holding hand, you have to move everything up with a force
equal and opposite to the weight of the stick and ball, and your hand hurts... If you jerk upwards
with the spring holding hand, initially, to spring will compress further, and the ball will remain
unmoved. The point being that that initial jerk upwards its translated not into the kinetic energy
of the bowling ball, but into a deforming force of the spring, and your hand doesnt hurt.

But then again - I'm not a physicist, though a good friend of mine has a Masters Degree in Physics,
and I'm sure he would like to get in on this discussion.

...

In fact - this is what he has to say about the subject. This should really be the last word
- please...

<CONTRIBUTION BY Marmite (BSc MSc Physics Hons)> Damage to the ground is directly related to
pressure, which can be calculated by dividing the Force by the Area of contact. A simple analogy is
try walking through a flower bed with boots and stilletoes, how much impact does each of them do?
The stilletoes will most likely sink straight in. In the case of the boots the force will be spread
over a larger area causeing the pressure reduce and stops you sinking into the ground (an extreme
example are snow boots).

In the case of a mountain bike, the area of contact is fixed (i.e the area of contact of the bike
wheels), although the effective area of contact is larger, which is due to the fact that the bike
isn't stationary, and any extra forces acting on the ground are spread over the area of distance
travelled for the duration the force is applied. When talking about damage to the underlying ground
you also need to talk about the Force. The larger the force on the ground, the more the damage. Now
looking at Newtons laws you can calculate the generalistic difference in the force between using
shock absorbers and without.

N1 - A body will remain at constant velocity unless acted upon by an external force. (i.e. the
acceleration of the bike relative to the ground is caused by bumps etc.). N2 - The force on the body
is directly proportional to the rate of change of momentum (i.e. mass * acceleration. The force on
the bike is related to the magnitude of the acceleration caused by the impact of bumps). N3 - Every
force applied to a body is matched by an equal and opposite force
(i.e. the Force on the bike = the force imposed on the ground).

If you don't have shock absorbers, the mass of the whole bike is accelerated sharply by any bumps in
the ground, hence the forces experienced by the bike due to that change in momentum (N2) and the
equal reaction force to the ground (N3) are high.

In the case of shock absorbers, the change in velocity is applied over a longer period, hence the
acceleration experienced by the wheels is less (acceleration = change in velocity / time), also for
the most part, it is only the mass of the wheels that accelerate up and down, and not the whole mass
of the bike. Therefore the actual change in momentum (N2) is less (as both the the mass and the
acceleration is less), the comparative force applied on the bike and rider
(N2) are therefore lower (giving a smoother ride) and hence reaction force and damage applied to the
ground (N3) is equally as low.

These fundamental laws are used in many other situations, for example crumple zones and air bags
lower the damage to the driver and the other body involved, by spreading the impact over a longer
time and hence lowering the force experienced by the driver. These fundamental properties in
question here may also be referred to as impulse. </CONTRIBUTION>

CandT
 
Jeff Strickland wrote:

>>But you don't know what that effect is. For example, standing still, the suspension is nothing but
>>ADDED DEAD WEIGHT.
>>
>>
>
>But standing still is nothing, it is simply standing still; this is no different than a hiker at
>rest. You said that the shock absorber adds shock to the ground because it is heavy, the fact is
>that shocks are not that much heavier than the solid parts they replace, and because they acutally
>absorb shocks, then the impact on the ground is lessened.
>
>
>
>
He'll squirm around that one one way or another. He seems incapable of visualizing lateral forces,
internal friction, inefficient mechanical linkages, etc. 'Spose he works for an insurance company?
Or an HMO?

Pete H

--
The best thing to do with a stupid remark is to not hear it.
R. Heinlein
 
On Tue, 08 Apr 2003 23:55:34 +0000, Mike Vandeman wrote:

> . .Pressure is always equal to the pressure in one's tires.
>
> So if you let all the air out of your tires, you bike will put ZERO pressure on the ground. BS.

Ummm... Yup. Since you can't ride with no pressure in your tires, your bike must be hanging on the
wall rack.

Obvious to everyone except PhDs, I guess.

(Physics wise, there is no such thing as ZERO pressure - at least not on Earth. You never let *all*
the air out of your tires, the pressure inside is equal to the pressure outside. But regardless, the
tire cannot support any weight unless the pressure inside exceed atmospheric by a large enough
margin to prevent flattening.

Obvious to everyone except PhDs.)

-Dondo
 
"CandT" <[email protected]> wrote in message
news:[email protected]...
| >
| >That defies the laws of physics. Both are equal.
| >
| ...
| >
| >It adds greater weight, hence greater force on the ground (vertically & horizontally, since they
| >are also ridden faster).
| >
|
| Hmmm, this thread does bring a smile to my face. I'm can't recall where Mr Vandeman's got his
| physics qualification, somewhere well respected I
assume, but
| I seemed to have taken in more from my Tertiary course here in the UK
(aged
| 16-17).
|
| OK - this is how a shock absorber works.
|
| A bike travelling forward hits a bump with the front wheel.
|
| On a non-suspended bike, the whole force of that contact is transferred
through
| the tyre (which has a slight damping effect, but for the sake of argument,
lets
| assume you are running wooden wheels!), forks, and riders arms, and indeed
there
| is an equal and opposite force transferred into the ground. (The ground it attempting to lift the
| entire weight of rider+bike)
|
| Now, on a suspended fork, the force of the contact is actually transferred
into
| a deforming force of the spring initially, and then is partially
disappated as
| heat, the compression of a gas, and sound in the shock 'absorbing' parts
of the
| fork. Only a portion of the force is returned to the ground. (Now, I know
not
| all forks have springs, sometimes its air, or elastomer, but the effect is
the
| same)
|
| Effectively, the rider+frame are treated as a seperate body to the
wheel+fork.
| They are both travelling forward with the same speed, and when a bump is contacted, the wheel and
| fork obtain a vertical accelleration which is
protected
| from the rider. The rider and frame still only have the forward motion.
(or
| actually a tiny downward motion with gravity, but ironically enough - the
faster
| the rider is going, and the better the shock absorbing technology, the
less that
| force will be !)
|
| Use this as an analogy. You are standing still holding a spring which is
50%
| compressed by the weight of a bowling ball on top. In the other hand you
have a
| stick with a bowling ball on top. If you quickly jerk upwards with the
stick
| holding hand, you have to move everything up with a force equal and
opposite to
| the weight of the stick and ball, and your hand hurts... If you jerk
upwards
| with the spring holding hand, initially, to spring will compress further,
and
| the ball will remain unmoved. The point being that that initial jerk
upwards its
| translated not into the kinetic energy of the bowling ball, but into a
deforming
| force of the spring, and your hand doesnt hurt.
|
| But then again - I'm not a physicist, though a good friend of mine has a
Masters
| Degree in Physics, and I'm sure he would like to get in on this
discussion.
|
| ...
|
| In fact - this is what he has to say about the subject. This should really
be
| the last word - please...
|
| <CONTRIBUTION BY Marmite (BSc MSc Physics Hons)> Damage to the ground is directly related to
| pressure, which can be
calculated by
| dividing the Force by the Area of contact. A simple analogy is try walking through a flower bed
| with boots and stilletoes, how much impact does each
of
| them do? The stilletoes will most likely sink straight in. In the case of
the
| boots the force will be spread over a larger area causeing the pressure
reduce
| and stops you sinking into the ground (an extreme example are snow boots).
|
| In the case of a mountain bike, the area of contact is fixed (i.e the area
of
| contact of the bike wheels), although the effective area of contact is
larger,
| which is due to the fact that the bike isn't stationary, and any extra
forces
| acting on the ground are spread over the area of distance travelled for
the
| duration the force is applied. When talking about damage to the underlying ground you also need to
| talk about the Force. The larger the force on the ground, the more the damage. Now looking at
| Newtons laws you can calculate
the
| generalistic difference in the force between using shock absorbers and
without.
|
| N1 - A body will remain at constant velocity unless acted upon by an
external
| force. (i.e. the acceleration of the bike relative to the ground is caused
by
| bumps etc.). N2 - The force on the body is directly proportional to the rate of change
of
| momentum (i.e. mass * acceleration. The force on the bike is related to
the
| magnitude of the acceleration caused by the impact of bumps). N3 - Every force applied to a body
| is matched by an equal and opposite
force
| (i.e. the Force on the bike = the force imposed on the ground).
|
| If you don't have shock absorbers, the mass of the whole bike is
accelerated
| sharply by any bumps in the ground, hence the forces experienced by the
bike due
| to that change in momentum (N2) and the equal reaction force to the ground
(N3)
| are high.
|
| In the case of shock absorbers, the change in velocity is applied over a
longer
| period, hence the acceleration experienced by the wheels is less
(acceleration =
| change in velocity / time), also for the most part, it is only the mass of
the
| wheels that accelerate up and down, and not the whole mass of the bike. Therefore the actual
| change in momentum (N2) is less (as both the the mass
and
| the acceleration is less), the comparative force applied on the bike and
rider
| (N2) are therefore lower (giving a smoother ride) and hence reaction force
and
| damage applied to the ground (N3) is equally as low.
|
| These fundamental laws are used in many other situations, for example
crumple
| zones and air bags lower the damage to the driver and the other body
involved,
| by spreading the impact over a longer time and hence lowering the force experienced by the driver.
| These fundamental properties in question here
may
| also be referred to as impulse. </CONTRIBUTION>
|
|
|
|
| CandT

Very well put and totally above that of MV I am sure. He is too scared to pass on his dissertation
to me to read, so I shall assume it does not exist.

Simon ..........I am sure HE will have some childlike retort.
 
"Mike Vandeman" <[email protected]> wrote in message
news:[email protected]...
| On Mon, 7 Apr 2003 16:33:12 +0100, "Simon" <[email protected]> wrote:
<snip that which mv cant understand>
|
| .Simon........doesnt the fact you ride a bike on paved streets negate your .whole ethos and
| arguments anyway?
|
| Why? I don't harm any wildlife there.
| ===

So the laying of streets and towns over "natural habitat" has caused no damage to wildlife?

Interesting

Simon
 
"CandT" <[email protected]> wrote in message
news:[email protected]...
> >
> >That defies the laws of physics. Both are equal.
> >
> ...
> >
> >It adds greater weight, hence greater force on the ground (vertically & horizontally, since they
> >are also ridden faster).
> >
>
> Hmmm, this thread does bring a smile to my face. I'm can't recall where Mr Vandeman's got his
> physics qualification, somewhere well respected I
assume, but
> I seemed to have taken in more from my Tertiary course here in the UK
(aged
> 16-17).
>
> OK - this is how a shock absorber works.
>
> A bike travelling forward hits a bump with the front wheel.
>
> On a non-suspended bike, the whole force of that contact is transferred
through
> the tyre (which has a slight damping effect, but for the sake of argument,
lets
> assume you are running wooden wheels!), forks, and riders arms, and indeed
there
> is an equal and opposite force transferred into the ground. (The ground it attempting to lift the
> entire weight of rider+bike)
>
> Now, on a suspended fork, the force of the contact is actually transferred
into
> a deforming force of the spring initially, and then is partially
disappated as
> heat, the compression of a gas, and sound in the shock 'absorbing' parts
of the
> fork. Only a portion of the force is returned to the ground. (Now, I know
not
> all forks have springs, sometimes its air, or elastomer, but the effect is
the
> same)
>
> Effectively, the rider+frame are treated as a seperate body to the
wheel+fork.
> They are both travelling forward with the same speed, and when a bump is contacted, the wheel and
> fork obtain a vertical accelleration which is
protected
> from the rider. The rider and frame still only have the forward motion.
(or
> actually a tiny downward motion with gravity, but ironically enough - the
faster
> the rider is going, and the better the shock absorbing technology, the
less that
> force will be !)
>
> Use this as an analogy. You are standing still holding a spring which is
50%
> compressed by the weight of a bowling ball on top. In the other hand you
have a
> stick with a bowling ball on top. If you quickly jerk upwards with the
stick
> holding hand, you have to move everything up with a force equal and
opposite to
> the weight of the stick and ball, and your hand hurts... If you jerk
upwards
> with the spring holding hand, initially, to spring will compress further,
and
> the ball will remain unmoved. The point being that that initial jerk
upwards its
> translated not into the kinetic energy of the bowling ball, but into a
deforming
> force of the spring, and your hand doesnt hurt.
>
> But then again - I'm not a physicist, though a good friend of mine has a
Masters
> Degree in Physics, and I'm sure he would like to get in on this
discussion.
>
> ...
>
> In fact - this is what he has to say about the subject. This should really
be
> the last word - please...
>
> <CONTRIBUTION BY Marmite (BSc MSc Physics Hons)> Damage to the ground is directly related to
> pressure, which can be
calculated by
> dividing the Force by the Area of contact. A simple analogy is try walking through a flower bed
> with boots and stilletoes, how much impact does each
of
> them do? The stilletoes will most likely sink straight in. In the case of
the
> boots the force will be spread over a larger area causeing the pressure
reduce
> and stops you sinking into the ground (an extreme example are snow boots).
>
> In the case of a mountain bike, the area of contact is fixed (i.e the area
of
> contact of the bike wheels), although the effective area of contact is
larger,
> which is due to the fact that the bike isn't stationary, and any extra
forces
> acting on the ground are spread over the area of distance travelled for
the
> duration the force is applied. When talking about damage to the underlying ground you also need to
> talk about the Force. The larger the force on the ground, the more the damage. Now looking at
> Newtons laws you can calculate
the
> generalistic difference in the force between using shock absorbers and
without.
>
> N1 - A body will remain at constant velocity unless acted upon by an
external
> force. (i.e. the acceleration of the bike relative to the ground is caused
by
> bumps etc.). N2 - The force on the body is directly proportional to the rate of change
of
> momentum (i.e. mass * acceleration. The force on the bike is related to
the
> magnitude of the acceleration caused by the impact of bumps). N3 - Every force applied to a body
> is matched by an equal and opposite
force
> (i.e. the Force on the bike = the force imposed on the ground).
>
> If you don't have shock absorbers, the mass of the whole bike is
accelerated
> sharply by any bumps in the ground, hence the forces experienced by the
bike due
> to that change in momentum (N2) and the equal reaction force to the ground
(N3)
> are high.
>
> In the case of shock absorbers, the change in velocity is applied over a
longer
> period, hence the acceleration experienced by the wheels is less
(acceleration =
> change in velocity / time), also for the most part, it is only the mass of
the
> wheels that accelerate up and down, and not the whole mass of the bike. Therefore the actual
> change in momentum (N2) is less (as both the the mass
and
> the acceleration is less), the comparative force applied on the bike and
rider
> (N2) are therefore lower (giving a smoother ride) and hence reaction force
and
> damage applied to the ground (N3) is equally as low.
>
> These fundamental laws are used in many other situations, for example
crumple
> zones and air bags lower the damage to the driver and the other body
involved,
> by spreading the impact over a longer time and hence lowering the force experienced by the driver.
> These fundamental properties in question here
may
> also be referred to as impulse. </CONTRIBUTION>
>
>
>
>
> CandT

Well. That sums that up, don't it? I certainly ain't got no more to say about that. ;-)
--
Westie --"Life is what happens while you're planning to do other things"--
 
Mike Vandeman <[email protected]> wrote in message
news:p[email protected]...
> On Tue, 8 Apr 2003 11:57:08 +0100, "Shaun Rimmer" <[email protected]>
wrote:
>
> . .Mike Vandeman <[email protected]> wrote in message
> .news:[email protected]... . .> .Please, if you wish to take this
> further, do study up on suspension .design, .> .action, and especially 'shock absorbers' - they do
> just what it says, .that .> .is, 'absorb shock', not absorb it then dish it straight back out into
the
> .> .ground. .> .> BS. By the laws of physics, they HAVE to apply the force to the ground, .unless
> .> they can FLY! . .They take in the sudden shock quickly, and apply it back slowly,
>
> That defies the laws of physics. Both are equal.

No it doesn't, no they aren't. Again, you are commenting on what you know nothing about. It's called
'shock absorption', and it utilises a viscous media (oil of a sort in these cases) and a perforated
and valved piece of metal. On compression, the valves open more, allowing easy passage of the 'oil'.
Upon re-bound, the valves close more, slowing the passage of said oil, and therefore the extension
of the suspension. This means the original sudden shock is absorbed quickly, then 'some' (most) of
it is released more slowly - less impact over a greater area, and less is given out than was first
encountered (some is retained in the shock absorber/suspension system as 'heat', some dissipated to
the air as vibration) in keeping with conservation of energy laws.

Here endeth today's lesson in layman's physics re: shock absorption, you total and utter dumbarse,
heheheheheh! ',;~}~

Shaun aRe
 
On Tue, 08 Apr 2003 20:04:20 -0400, PeterH <[email protected]> wrote:

.Mike Vandeman wrote: . .> .>But you don't know what that effect is. For example, standing still,
the .>suspension is nothing but ADDED DEAD WEIGHT. .> .> .> .This thread concerned, at one time, the
effects of an activity. F=MA . .Dead weight does not enter that rather straightforward equation.

Thanks for showing your complete ignorance of physics. Gravity IS an acceleration! So dead weight is
caused by gravity. DUH!

.Pete H

===
I am working on creating wildlife habitat that is off-limits to humans ("pure habitat"). Want to
help? (I spent the previous 8 years fighting auto dependence and road construction.)

http://home.pacbell.net/mjvande
 
On Tue, 8 Apr 2003 17:22:24 -0700, "Jeff Strickland" <[email protected]> wrote:

. ."Mike Vandeman" <[email protected]> wrote in message
.news:[email protected]... .> On Mon, 7 Apr 2003 12:46:07 -0700, "Jeff
Strickland" <[email protected]> .wrote: .> .> . .> ."Mike Vandeman" <[email protected]> wrote in
message .> .news:[email protected]... .> .> On Fri, 4 Apr 2003 14:43:05
-0800, "Jeff Strickland" <[email protected]> .> .wrote: .> .> .> .> ."Mike Vandeman"
<[email protected]> wrote in message .> .> .news:[email protected]... .>
.> .> On 3 Apr 2003 21:30:56 -0800, [email protected] (Terri Alvillar) .wrote: .> .> .> .> .> .> .I
wonder if any studies have been done to correlate mountain bike .> .> .> .equipment shock absorbers
and suspension with damage to terrain? .Is .> .> .> .the damage to terrain commensurate with the
level of shock .absorbing .> .> .> .technology on the vehicle? .> .> .> .> .> .> Yes. By Newton's
laws of physics, every action has an equal and .> .opposite .> .> .> reaction. In other words, the
force applied to the ground (or .anything .> .> .else in .> .> .> their path, such as a plant,
animal, or person) is identical to the .> .force .> .> .> applied to the bike. The reason that
mountain bikes are built much .> .> .stronger than .> .> .> normal bikes is that they encounter much
greater FORCES. Therefore, .> .they .> .> .apply .> .> .> much greater forces to the ground &
everything else in their path. .QED .> .> . .> .> .Technically, a mountain bike with a shock
absorber should have less of .an .> .> .impact than one without a shock absorber. Think of the words
being .used .> .> .here, SHOCK ABSORBER. A shock absorber absorbs shocks, therefore by .> .>
.definition, less of an impact. .> .> . .> .> .Think of the water barrels they (CalTrans or others)
place on the .> .> .impact-side of a sign or post. The sign or post might weigh more, but .the .> .>
.impact upon objects that strike the sign or post is lessened. In the .> .world .> .> .of bikes and
dirt, the dirt is the object that constantly stirkes the .> .bike .> .> .(trying to keep the analogy
straight), or in other words, the impact .of .> .the .> .> .bike striking the ground repeatedly is
lessened because of the shock .> .> .absorber. Newton's Law does not take into account the affects
of .external .> .> .forces, such as a shock absorber. .> .> .> .> Oh sure. Newton's laws don't apply
to mountain bikes. That is the .funniest .> .thing .> .> I have heard in a long time! Idiot. .> . .>
.I never said Newton's laws don't apply, what I said is that the .simplistic .> .application of them
omits the affect of the shock absorber. .> .> But you don't know what that effect is. For example,
standing still, the .> suspension is nothing but ADDED DEAD WEIGHT. . .But standing still is
nothing, it is simply standing still; this is no .different than a hiker at rest. You said that the
shock absorber adds shock .to the ground because it is heavy, the fact is that shocks are not that
much .heavier than the solid parts they replace, and because they acutally absorb .shocks, then the
impact on the ground is lessened.

So you admit that shoch absorbers add weight! QED
===
I am working on creating wildlife habitat that is off-limits to humans ("pure habitat"). Want to
help? (I spent the previous 8 years fighting auto dependence and road construction.)

http://home.pacbell.net/mjvande
 
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