They're teaching me strange things in school. Can anyone explain why a point at the top of a rolling
bicycle wheel moves twice as fast as a point in the center of the wheel? And if you can wrap your
head around that one... why is a point at the bottom of a bicycle wheel not moving at all?

Here's the model I found in the textbook to explain it:

http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg

-John Morgan

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:
>
> http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
>
> -John Morgan
>
>

So that's why Crossmax wheels suck. ;^)

Mike

John Morgan said...

> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:
>
> http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
>
> -John Morgan

In those physics drawings the arrows on the small drawings are added together to get the arrows on
the big drawing. The arrows going in the same direction add to make a longer arrow (the velocities
are added, doubling them), while the arrows going in opposite directions cancel out.

Put another way, a wheel has both angular (rotational) and linear motion. At the top of the wheel,
the angular motion has the same direction as the linear motion of the entire bike, and the point at
the very top is moving twice as fast as the forward motion of you and the rest of the bike. You can
see this whenever you have something stuck to your tire. You can see the spot moving away from you
when it gets to the top half of the tire. It must be moving faster than you are, or you wouldn't be
able to see it moving away from you. When it gets to the bottom half of the tire, it moves toward
you, so it has less speed than you do.

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:
>
> http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
>
> -John Morgan

now ask them about the load in the spokes!

Jon Bond

Some of this has to do with Angular Momentum... It's what allows you to ride a bicycle easily when
the wheels are rotating, but fall over when they stop (unless you can track stand.)

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:
>
> http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
>
> -John Morgan

> In those physics drawings the arrows on the small drawings are added together to get the arrows on
> the big drawing. The arrows going in the same direction add to make a longer arrow (the velocities
> are added, doubling them), while the arrows going in opposite directions cancel out.

LOL! I know, I'm the one who drew the arrows! =)

> Put another way, a wheel has both angular (rotational) and linear motion. At the top of the wheel,
> the angular motion has the same direction as the linear motion of the entire bike, and the point
> at the very top is moving twice as fast as the forward motion of you and the rest of the bike. You
> can see this whenever you have something stuck to your tire. You can see the spot moving away from
> you when it gets to the top half of the tire. It must be moving faster than you are, or you
> wouldn't be able to see it moving away from you. When it gets to the bottom half of the tire, it
> moves toward you, so it has less speed than you do.

This is the best explaination I have heard of this concept so far! Way to break it down into
layman's terms, SS. It just boggles my mind that the top part of a wheel moves with a different
speed than the bottom part!

-John Morgan

Actually, a lot of the staying upright phenomenon has to do with the trail of the front wheel. Not
all of it, but a lot. This is why even if you're moving backwards really frickin' fast, you're gonna
go down. Hard.

Jon Bond

<markh12001@charter.net> wrote in message news:vs8577p9v8ka59@corp.supernews.com...
> Some of this has to do with Angular Momentum... It's what allows you to
ride
> a bicycle easily when the wheels are rotating, but fall over when they
stop
> (unless you can track stand.)
>
> "John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> > They're teaching me strange things in school. Can anyone explain why a point at the top of a
> > rolling bicycle wheel moves twice as fast as a
point
> > in the center of the wheel? And if you can wrap your head around that one... why is a point at
> > the bottom of a bicycle wheel not moving at
all?
> >
> > Here's the model I found in the textbook to explain it:
> >
> > http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
> >
> > -John Morgan
> >
>

"Michael Dart" <mrdart@erols.com> wrote in message news:bq11gs01nk4@enews4.newsguy.com...
> So that's why Crossmax wheels suck. ;^)

I wish I'd seen this before I got my Crossmax wheels....<heavy sigh> It's just like so,... logical.
--
Westie (Replace 'invalid' with 'yahoo' when replying.)

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:
>
> http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
>

Yeah! I love that stuff. Keep it comin!

Matt

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:
>
> http://members.cox.net/jhnmorgan/mtb/rollingphysics.jpg
>
> -John Morgan
>
>

If you really want some fun post this over on rec.bicycles.tech.

Mike

On Wed, 26 Nov 2003 03:49:58 +0000, Jon Bond wrote:

> Actually, a lot of the staying upright phenomenon has to do with the trail of the front wheel. Not
> all of it, but a lot. This is why even if you're moving backwards really frickin' fast, you're
> gonna go down. Hard.

You need to learn how to ride fakie

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:<DRUwb.7470$9O5.6511@fed1read06>...

> This is the best explaination I have heard of this concept so far! Way to break it down into
> layman's terms, SS. It just boggles my mind that the top part of a wheel moves with a different
> speed than the bottom part!
>
> -John Morgan

Be careful. In the picture at the top left of the diagram, the top and bottom of the wheel actually
have the same speed, but they have different velocities. This would be the situation that occurs if
you were to detach the wheel from the bicycle, hold it by the axle and spin it. In this case the top
and bottom of the wheel are like mirror images. They're both doing the same thing, but in opposite
directions.

Now when you put the wheel back on the bike and take into account the fact that the whole bicycle is
moving forward, then the forward velocity of the bike will cancel the backward velocity of the
bottom of the wheel, which gives the bottom of the wheel a velocity of 0. But the velocity of the
top of the wheel gets added to the velocity of the bike, so the top of the wheel will have a
velocity of 2V.

I know you already figured all this out, but for your future adventures in physics it's worth
keeping in mind that speed and velocity are different critters. It's also important in physics to
keep track of the system of reference, i.e. it's one thing to look at the wheel by itself, and
another think to look at the wheel when it's attached to the bike.

Brad Carmichael

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06... ...
why is a point at the bottom of a bicycle wheel not moving at all?

Vector diagrams are fine and all, but let's not forget the obvious...

"A point at the bottom of a bicycle wheel is not moving at all because it is in contact with
the ground."

(Insert usual disclaimers about assuming bike is not airborne, assuming wheel is not skidding,
assuming ground is the reference point, even though its moving very very quickly relative to some
things etc etc)

grum

"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
> They're teaching me strange things in school. Can anyone explain why a point at the top of a
> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
> moving at all?
>
> Here's the model I found in the textbook to explain it:

Piece o' piss - it's all relative! Rate of motion in this case is relative to the ground, the bottom
of the wheel is _on_ the ground, and therefore not moving. The top of the wheel is in motion
relative to the centre of the wheel, which is half way between top and bottom, therefore it's moving
twice as fast. Duh!

',;~}~

Shaun aRe - Have a nice day now y'all, y'hear?

On Fri, 28 Nov 2003 13:47:37 -0000, "Shaun Rimmer" <shaun@newtronic.co.uk> wrote:

>
>"John Morgan" <jhnmorgan@NOSPAMcox.net> wrote in message news:KrTwb.7460$9O5.4033@fed1read06...
>> They're teaching me strange things in school. Can anyone explain why a point at the top of a
>> rolling bicycle wheel moves twice as fast as a point in the center of the wheel? And if you
>> can wrap your head around that one... why is a point at the bottom of a bicycle wheel not
>> moving at all?
>>
>> Here's the model I found in the textbook to explain it:
>
>Piece o' piss - it's all relative! Rate of motion in this case is relative to the ground, the
>bottom of the wheel is _on_ the ground, and therefore not moving. The top of the wheel is in motion
>relative to the centre of the wheel, which is half way between top and bottom, therefore it's
>moving twice as fast. Duh!
>
>',;~}~
>
>
>Shaun aRe - Have a nice day now y'all, y'hear?

Yeah, what he said!

Peace, Bill

...one speed to rule them all, one speed to find them, one speed to bring them all and on the trails
pass them In the Land of Avalon where the geared pigs lie...