# OT MV related:Gravity lesson

Discussion in 'Mountain Bikes' started by Simon, Apr 11, 2003.

Not open for further replies.
1. ### Simon Guest

In recent days many have had the fun of trying to educate MV on the effects of gravity. His main
argument is thus:

Bikes with shock absorbers weigh more and hence cause more damage to trails.

Anyone with a mere basic understanding of physics will say this is absolutely wrong. Some people
with a little more physics knowledge (Mike himself) will say this is true. Whilst those with a firm
understanding of physics will say its laughably incorrect.

Here's why:

Acceleration due to gravity is 9.8 m/s/s we all know this..There are slight variations in this
numerical value (to the second decimal place) which are dependent primarily upon altitude.

Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
force. This is true in itself, its obvious.

However mike then says that the acceleration (a) is gravity. This is where he has shown no

If we let him have the fact that (a) is indeed gravity we all know that acceleration due to gravity
is constant regardless of mass. In other words a bike and a hiker both will accelerate at the same
speed due to gravity when in a free fall situation.

Therefore it can be seen that mike is very confused with regards to physics and has a tendency to
change his argument when cornered.

Its all good fun and yes the above is verifiable should anyone require it.

Simon.........I like mike, he makes me look good. We should market him as an accessory.

Tags:

2. ### Simon Guest

Not a reply to my own post just did not wish to start another but.......

I was just thinking the more we keep Mike V here the less time he has to annoy people out in the
wild. So I guess we are in fact doing mtb'ers of the world a favour.

3. ### Bomba Guest

Simon wrote:

> Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
> force. This is true in itself, its obvious.
>
> However mike then says that the acceleration (a) is gravity. This is where he has shown no
>
> If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
> gravity is constant regardless of mass. In other words a bike and a hiker both will accelerate at
> the same speed due to gravity when in a free fall situation.
>
> Therefore it can be seen that mike is very confused with regards to physics and has a tendency to
> change his argument when cornered.

Ok, my physics isn't that good, I'll play.

If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
proportional mass?

4. ### Simon Guest

"bomba" <[email protected]> wrote in message news:[email protected]...
| Simon wrote:
|
| > Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
| > force. This is true in itself, its obvious.
| >
| > However mike then says that the acceleration (a) is gravity. This is
where
| > he has shown no understanding of advanced physics.
| >
| > If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
| > gravity is constant regardless of mass. In other
words a
| > bike and a hiker both will accelerate at the same speed due to gravity
when
| > in a free fall situation.
| >
| > Therefore it can be seen that mike is very confused with regards to
physics
| > and has a tendency to change his argument when cornered.
|
| Ok, my physics isn't that good, I'll play.
|
| If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
| proportional mass?
|
I am not talking that at all. Mike is and thats why he is wrong and his knowledge is flawed. He is
trying to substitute incorrect sections within standard equations.

Its all topsy turvy

Simon.........prefers to think bike goes up+bike comes down=fun

5. ### John Harlow Guest

> > Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
> > force. This is true in itself, its obvious.
> >
> > However mike then says that the acceleration (a) is gravity. This is
where
> > he has shown no understanding of advanced physics.
> >
> > If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
> > gravity is constant regardless of mass. In other
words a
> > bike and a hiker both will accelerate at the same speed due to gravity
when
> > in a free fall situation.
> >
> > Therefore it can be seen that mike is very confused with regards to
physics
> > and has a tendency to change his argument when cornered.
>
> Ok, my physics isn't that good, I'll play.
>
> If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
> proportional mass?

Shock Absorbers work by converting a high force short duration impact into a lower force long
duration impact. Without a shock absorber, the peak impact force is far greater than with one, but
for a shorter time period. This high peak shock impact is the principle which jackhammers use to
destroy concrete; a jackhammer with a shock absorber would be ineffective.

Specifically; Force (Shock Absorber) Decelleration g's (in gravitational units)
-----------------------------------
Impact weight (Shock Absorber)

So, one can see by increasing the impact weight *of the shock absorber* the number of g's
are reduced.

Effective Impact weight (We) can be expressed as:

5.36 Fd S We = -------- V^2

where Fd is Drive force (rider weight in lbs), S is Shock Absorber stroke length (inches), and V is
Linear Velocity of the impact of the Shock Absorber (ft/sec)

Therefore, either a longer stroke or lower rider weight will reduce G forces to the wheel. A
hardtail (zero stroke length) has the highest impact force.

6. ### Bomba Guest

Simon wrote:

> | If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
> | proportional mass?
> |
> I am not talking that at all. Mike is and thats why he is wrong and his knowledge is flawed. He is
> trying to substitute incorrect sections within standard equations.

You've totally lost me. Are you now saying that A can not be replaced with gravity?

I haven't read any of Mike's posts on this subject, but your post seems totally wrong, and justifies
Mike's position. I can't see anything wrong with asserting that extra weight leads to more force.
It's a simplistic view, but it stands up to (my knowledge of) the laws of physics.

7. ### Simon Guest

"John Harlow" <[email protected]> wrote in message
news:[email protected]...
|
|
| > > Mike argues that since "force (f)= mass (m) x acceleration (a)" a
larger
| > > mass will create more force. This is true in itself, its obvious.
| > >
| > > However mike then says that the acceleration (a) is gravity. This is
| where
| > > he has shown no understanding of advanced physics.
| > >
| > > If we let him have the fact that (a) is indeed gravity we all know
that
| > > acceleration due to gravity is constant regardless of mass. In other
| words a
| > > bike and a hiker both will accelerate at the same speed due to gravity
| when
| > > in a free fall situation.
| > >
| > > Therefore it can be seen that mike is very confused with regards to
| physics
| > > and has a tendency to change his argument when cornered.
| >
| > Ok, my physics isn't that good, I'll play.
| >
| > If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
| > proportional mass?
|
| Shock Absorbers work by converting a high force short duration impact into
a
| lower force long duration impact. Without a shock absorber, the peak
impact
| force is far greater than with one, but for a shorter time period. This high peak shock impact is
| the principle which jackhammers use to destroy concrete; a jackhammer with a shock absorber would
| be ineffective.
|
| Specifically; Force (Shock Absorber) Decelleration g's (in gravitational units)
| -----------------------------------
| Impact weight (Shock Absorber)
|
| So, one can see by increasing the impact weight *of the shock absorber*
the
| number of g's are reduced.
|
| Effective Impact weight (We) can be expressed as:
|
| 5.36 Fd S We = -------- V^2
|
| where Fd is Drive force (rider weight in lbs), S is Shock Absorber stroke length (inches), and V
| is Linear Velocity of the impact of the Shock Absorber (ft/sec)
|
| Therefore, either a longer stroke or lower rider weight will reduce G
forces
| to the wheel. A hardtail (zero stroke length) has the highest impact force.

He's(mv) been told, just refuses to believe it. I fail to see who can n ot understand that. I have a
4 year old that can grasp the basics.

Simon

8. ### Simon Guest

"bomba" <[email protected]> wrote in message news:[email protected]...
| Simon wrote:
|
| > | If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
| > | proportional mass?
| > |
| > I am not talking that at all. Mike is and thats why he is wrong and his knowledge is flawed. He
| > is trying to substitute incorrect sections
within
| > standard equations.
|
| You've totally lost me. Are you now saying that A can not be replaced with gravity?
|
| I haven't read any of Mike's posts on this subject, but your post seems totally wrong, and
| justifies Mike's position. I can't see anything wrong with asserting that extra weight leads to
| more force. It's a simplistic view, but it stands up to (my knowledge of) the laws of
physics.
|
|

Okay firstly if you have not read (reads been entertained) by mikes posts its difficult to follow i
agree. He has basically taken a standard equation and revised it as and when the argument changes. I
am not trying to allay his claims or re-enforce them. Guess I am just rambling out loud.

Simon.........loves the amusement side of newgroups.

9. ### Dick Guest

Me thinks an easier way to prove that shocks save (or don't save) dirt would be to make a suspension
shovel and see how well it digs.

Simon wrote:
> In recent days many have had the fun of trying to educate MV on the effects of gravity. His main
> argument is thus:
>
> Bikes with shock absorbers weigh more and hence cause more damage to trails.
>
> Anyone with a mere basic understanding of physics will say this is absolutely wrong. Some people
> with a little more physics knowledge (Mike himself) will say this is true. Whilst those with a
> firm understanding of physics will say its laughably incorrect.
>
> Here's why:
>
> Acceleration due to gravity is 9.8 m/s/s we all know this..There are slight variations in this
> numerical value (to the second decimal place) which are dependent primarily upon altitude.
>
> Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
> force. This is true in itself, its obvious.
>
> However mike then says that the acceleration (a) is gravity. This is where he has shown no
>
> If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
> gravity is constant regardless of mass. In other words a bike and a hiker both will accelerate at
> the same speed due to gravity when in a free fall situation.
>
> Therefore it can be seen that mike is very confused with regards to physics and has a tendency to
> change his argument when cornered.
>
> Its all good fun and yes the above is verifiable should anyone require it.
>
> Simon.........I like mike, he makes me look good. We should market him as an accessory.

"Simon" <[email protected]> wrote in message
news:[email protected]...
>
> In recent days many have had the fun of trying to educate MV on the
effects
> of gravity.

Simple version:

Take two pairs of forks, one set of Marzocci Monster T's with soft springs in, one pair of rigids.
Add weight to the rigids until both forks weight the same. Hit Mike V. on the head with said forks.
Which one feels best Mikey?

Steve E.

11. ### Simon Guest

"spademan o---[) *" <[email protected]> wrote in message
news:[email protected]...
|
| "Simon" <[email protected]> wrote in message
| news:[email protected]...
| >
| > In recent days many have had the fun of trying to educate MV on the
| effects
| > of gravity.
|
| Simple version:
|
| Take two pairs of forks, one set of Marzocci Monster T's with soft springs in, one pair of rigids.
| Add weight to the rigids until both forks weight
the
| same. Hit Mike V. on the head with said forks. Which one feels best Mikey?
|
| Steve E.
|
|
Ohhhhhhhh now you done it. He will report you to your isp for death threats now.lol

I like it though

Simon

12. ### Corvus Corvax Guest

"Simon" <[email protected]> wrote
>
> Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
> force. This is true in itself, its obvious.

Yes, this is correct.

> However mike then says that the acceleration (a) is gravity. This is where he has shown no

I'm not sure what "advanced physics" is like on your planet, but Mike is also correct here. "a" is
the gravitational acceleration, for a stationary bike, or for one rolling on a smooth surface.

> If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
> gravity is constant regardless of mass. In other words a bike and a hiker both will accelerate at
> the same speed due to gravity when in a free fall situation.

Both _will_ accelerate at the same rate in free fall. Your point is?

> Therefore it can be seen that mike is very confused with regards to physics and has a tendency to
> change his argument when cornered.

Wow. Uh, what?

CC

13. ### W K Guest

"John Harlow" <[email protected]> wrote in message news:tOzla.91905

<snip>

> Therefore, either a longer stroke or lower rider weight will reduce G
forces
> to the wheel. A hardtail (zero stroke length) has the highest impact force.

All true, but I bet you ride harder and make up for the difference.

BTW is there a better expression for "G forces" ? "Forces caused by rapid decelleration" perhaps?

14. ### W K Guest

"bomba" <[email protected]> wrote in message news:[email protected]...
> Simon wrote:
>
> > | If you're taking F=MA and A is a constant (9.8 m/s), then surely force is directionally
> > | proportional mass?
> > |
> > I am not talking that at all. Mike is and thats why he is wrong and his knowledge is flawed. He
> > is trying to substitute incorrect sections
within
> > standard equations.
>
> You've totally lost me. Are you now saying that A can not be replaced with gravity?
>
> I haven't read any of Mike's posts on this subject, but your post seems totally wrong, and
> justifies Mike's position. I can't see anything wrong with asserting that extra weight leads to
> more force. It's a simplistic view, but it stands up to (my knowledge of) the laws of
physics.

I'd suggest that gravity should be described as being 9.8 N/Kg. So, a 100kg bike+rider has a
downward force of 9800 N. And thats nothing to do with F=MA if you aren't moving (downwards).

But as soon as theres nothing under said bike it'll start hurtling towards the earth at.... F=MA ...
9800 = 100 x accelleration. hey presto 9.8 m/s

Accelleration and gravity get freely and incorrecly mixed. "pulling 5G" or whatever means you are
accellerating at 50ish m/s /s and you get forces that feel like 5x gravity.

Where did this start again?

15. ### Simon Guest

"Corvus Corvax" <[email protected]> wrote in message
news:[email protected]...
| "Simon" <[email protected]> wrote
| >
| > Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
| > force. This is true in itself, its obvious.
|
| Yes, this is correct.
|
| > However mike then says that the acceleration (a) is gravity. This is
where
| > he has shown no understanding of advanced physics.
|
| I'm not sure what "advanced physics" is like on your planet, but Mike is also correct here. "a" is
| the gravitational acceleration, for a stationary bike, or for one rolling on a smooth surface.
|
| > If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
| > gravity is constant regardless of mass. In other
words a
| > bike and a hiker both will accelerate at the same speed due to gravity
when
| > in a free fall situation.
|
| Both _will_ accelerate at the same rate in free fall. Your point is?
|
| > Therefore it can be seen that mike is very confused with regards to
physics
| > and has a tendency to change his argument when cornered.
|
| Wow. Uh, what?
|
| CC

Acceleration is not gravity. (a) is often referred to as acceleration DUE to gravity.

http://www.physicsclassroom.com/Class/1DKin/U1L5e.html

Simon

16. ### Mike Vandeman Guest

On Fri, 11 Apr 2003 13:35:55 +0100, "Simon" <[email protected]> wrote:

. .In recent days many have had the fun of trying to educate MV on the effects .of gravity. His main
argument is thus: . .Bikes with shock absorbers weigh more and hence cause more damage to trails. .
.Anyone with a mere basic understanding of physics will say this is .absolutely wrong. Some people
with a little more physics knowledge (Mike .himself) will say this is true. Whilst those with a firm
understanding of .physics will say its laughably incorrect. . .Here's why: . .Acceleration due to
gravity is 9.8 m/s/s we all know this..There are slight .variations in this numerical value (to the
second decimal place) which are .dependent primarily upon altitude. . .Mike argues that since "force
(f)= mass (m) x acceleration (a)" a larger .mass will create more force. This is true in itself, its
obvious. . .However mike then says that the acceleration (a) is gravity. This is where .he has shown

You are LYING. I said that gravity is an acceleration, not the reverse.

.If we let him have the fact that (a) is indeed gravity we all know that .acceleration due to
gravity is constant regardless of mass. In other words a .bike and a hiker both will accelerate at
the same speed due to gravity when .in a free fall situation.

Right, but the FORCE applied to the ground will be greater, from the greater mass. DUH!

===
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

17. ### Westie Guest

"Simon" <[email protected]> wrote in message
news:[email protected]...
>
> In recent days many have had the fun of trying to educate MV on the
effects
> of gravity. His main argument is thus:
>
> Bikes with shock absorbers weigh more and hence cause more damage to
trails.
>
> Anyone with a mere basic understanding of physics will say this is absolutely wrong. Some people
> with a little more physics knowledge (Mike himself) will say this is true. Whilst those with a
> firm understanding of physics will say its laughably incorrect.
>
> Here's why:
>
> Acceleration due to gravity is 9.8 m/s/s we all know this..There are
slight
> variations in this numerical value (to the second decimal place) which are dependent primarily
> upon altitude.
>
> Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger mass will create more
> force. This is true in itself, its obvious.
>
> However mike then says that the acceleration (a) is gravity. This is where he has shown no
>
> If we let him have the fact that (a) is indeed gravity we all know that acceleration due to
> gravity is constant regardless of mass. In other words
a
> bike and a hiker both will accelerate at the same speed due to gravity
when
> in a free fall situation.
>
> Therefore it can be seen that mike is very confused with regards to
physics
> and has a tendency to change his argument when cornered.
>
> Its all good fun and yes the above is verifiable should anyone require it.
>
> Simon.........I like mike, he makes me look good. We should market him as
an
> accessory.
>
>

As much as I don't want to agree with MV, I think that he was trying to say that a heavier bike
creates more damage when it hits the ground. Which on it's own is probably true. But as John
explains in another thread posted here, the suspension spreads out that force. So while MV is right
in his own way, he conveniently ignores other parts of the debate that, when taken into
consideration, make all the difference. And _that's_ a standard MV technique.
--
Westie --"Life is what happens while you're planning to do other things"--

18. ### Mike Vandeman Guest

On Fri, 11 Apr 2003 14:53:08 +0200, bomba <[email protected]> wrote:

.Simon wrote: . .> Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger .> mass
will create more force. This is true in itself, its obvious. .> .> However mike then says that the
acceleration (a) is gravity. This is where .> he has shown no understanding of advanced physics. .>
.> If we let him have the fact that (a) is indeed gravity we all know that .> acceleration due to
gravity is constant regardless of mass. In other words a .> bike and a hiker both will accelerate at
the same speed due to gravity when .> in a free fall situation. .> .> Therefore it can be seen that
mike is very confused with regards to physics .> and has a tendency to change his argument when
cornered. . .Ok, my physics isn't that good, I'll play. . .If you're taking F=MA and A is a constant
(9.8 m/s), then surely force .is directionally proportional mass?

BINGO! You are on your way to enlightenment. Or maybe that was IT!
===
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

19. ### Mike Vandeman Guest

On Fri, 11 Apr 2003 13:54:34 GMT, "John Harlow" <[email protected]> wrote:

. . .> > Mike argues that since "force (f)= mass (m) x acceleration (a)" a larger .> > mass will
create more force. This is true in itself, its obvious. .> > .> > However mike then says that the
acceleration (a) is gravity. This is .where .> > he has shown no understanding of advanced physics.
.> > .> > If we let him have the fact that (a) is indeed gravity we all know that .> > acceleration
due to gravity is constant regardless of mass. In other .words a .> > bike and a hiker both will
accelerate at the same speed due to gravity .when .> > in a free fall situation. .> > .> > Therefore
it can be seen that mike is very confused with regards to .physics .> > and has a tendency to change
his argument when cornered. .> .> Ok, my physics isn't that good, I'll play. .> .> If you're taking
F=MA and A is a constant (9.8 m/s), then surely force .> is directionally proportional mass? .
.Shock Absorbers work by converting a high force short duration impact into a .lower force long
duration impact.

BS. You can't "lower" the force of gravity. The bike may bounce, but eventually it has to hit the
ground, with the full force of gravity. PLUS its momentum.

Without a shock absorber, the peak impact .force is far greater than with one, but for a shorter
time period. This .high peak shock impact is the principle which jackhammers use to destroy
.concrete; a jackhammer with a shock absorber would be ineffective. . .Specifically;
. Force .(Shock Absorber)
.Decelleration g's (in
gravitational units)
. -----------------------------------
. Impact .weight (Shock Absorber) .
.So, one can see by increasing the
impact weight *of the shock
absorber* the .number of g's are
reduced. . .Effective Impact weight
(We) can be expressed as: .
. 5.36 Fd S .We = --------
. V^2 . .where Fd is Drive force (rider weight in lbs), S is Shock Absorber stroke
.length (inches), and V is Linear Velocity of the impact of the Shock .Absorber
(ft/sec) . .Therefore, either a longer stroke or lower rider weight will reduce G
forces .to the wheel. A hardtail (zero stroke length) has the highest impact
.force. . . .

===
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

20. ### Mike Vandeman Guest

On Fri, 11 Apr 2003 15:48:46 +0200, bomba <[email protected]> wrote:

.Simon wrote: . .> | If you're taking F=MA and A is a constant (9.8 m/s), then surely force .> | is
directionally proportional mass? .> | .> I am not talking that at all. Mike is and thats why he is
wrong and his .> knowledge is flawed. He is trying to substitute incorrect sections within .>
standard equations. . .You've totally lost me. Are you now saying that A can not be replaced .with
gravity? . .I haven't read any of Mike's posts on this subject, but your post seems .totally wrong,
and justifies Mike's position. I can't see anything .wrong with asserting that extra weight leads to
more force. It's a .simplistic view, but it stands up to (my knowledge of) the laws of physics.

Careful, mountain bikers can't take too much reality....
===
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