Bicycle Wheel Physics

[John Morgan]

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]

"John Morgan" > 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

[Super Slinky]

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.

[Jon Bond]

"John Morgan" > 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" > 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
>
>

[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

[Jon Bond]

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

> wrote in message
...
> 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" > 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
> >
> >
>
>

[Westie]

"Michael Dart" > wrote in message
...
> 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.)

[MattB]

"John Morgan" > 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

[Michael Dart]

"John Morgan" > 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

[bomba]

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 :)

[Brad Carmichael]

"John Morgan" > 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

[grum]

"John Morgan" > 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

[Shaun Rimmer]

"John Morgan" > 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' **** - 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?

[Bill Wheeler]

On Fri, 28 Nov 2003 13:47:37 -0000, "Shaun Rimmer"
> wrote:

>
>"John Morgan" > 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' **** - 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...

[Shaun Rimmer]

"Bill Wheeler" > wrote in message
...
> On Fri, 28 Nov 2003 13:47:37 -0000, "Shaun Rimmer"
> > wrote:
>
> >
> >"John Morgan" > 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' **** - 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!

Yay! What he said about what I 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...


Blah-blah-blah-blah.

Shaun aRe - Some things never change, Like Wheeler. And his gears.

[Bill Wheeler]

On Mon, 1 Dec 2003 16:20:03 -0000, "Shaun Rimmer"
> wrote:


>
>Shaun aRe - Some things never change, Like Wheeler. And his gears.
>

Don't got any gears to change ;-P
....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...

[Michael Dart]

"Bill Wheeler" > wrote in message
...
> On Mon, 1 Dec 2003 16:20:03 -0000, "Shaun Rimmer"
> > wrote:
>
>
> >
> >Shaun aRe - Some things never change, Like Wheeler. And his gears.
> >
>
> Don't got any gears to change ;-P

That's your problem Bill. You're just limiting yourself. Many of the
others here with SS's also have full geared boingers. C'mon now you did
real good with the disc brake thing.

Mike - free your mind and your ass will follow.

[Shaun Rimmer]

"Bill Wheeler" > wrote in message
...
> On Mon, 1 Dec 2003 16:20:03 -0000, "Shaun Rimmer"
> > wrote:
>
>
> >
> >Shaun aRe - Some things never change, Like Wheeler. And his gears.
> >
>
> Don't got any gears to change ;-P

Yes - it's still 'gearing' dude - gears are what set the ratio.


Shaun aRe

[bomba]

On Wed, 03 Dec 2003 13:08:30 +0000, Shaun Rimmer wrote:

>> Don't got any gears to change ;-P
>
> Yes - it's still 'gearing' dude - gears are what set the ratio.

Perhaps you missed it, but Bill's now given up on the whole new-fangled
'gear' thing and gone back to *true* riding. He's now got a hobby
horse.

--
a.m-b FAQ: http://www.j-harris.net/bike/ambfaq.htm

a.bmx FAQ: http://www.t-online.de/~jharris/bmx_faq.htm

[Michael Dart]

"bomba" > wrote in message
...
> On Wed, 03 Dec 2003 13:08:30 +0000, Shaun Rimmer wrote:
>
> >> Don't got any gears to change ;-P
> >
> > Yes - it's still 'gearing' dude - gears are what set the ratio.
>
> Perhaps you missed it, but Bill's now given up on the whole new-fangled
> 'gear' thing and gone back to *true* riding. He's now got a hobby
> horse.
>

No ****ing Gears!

http://www.sciencetech.technomuses.ca/english/collection/images/litho.jpg

Mike ;^)

[bomba]

On Wed, 03 Dec 2003 17:03:02 -0500, Michael Dart wrote:

>> Perhaps you missed it, but Bill's now given up on the whole new-fangled
>> 'gear' thing and gone back to *true* riding. He's now got a hobby
>> horse.
>>
>
> No ****ing Gears!
>
> http://www.sciencetech.technomuses.ca/english/collection/images/litho.jpg

Yep, that's a hobby horse...

--
a.m-b FAQ: http://www.j-harris.net/bike/ambfaq.htm

a.bmx FAQ: http://www.t-online.de/~jharris/bmx_faq.htm

[Shaun Rimmer]

"bomba" > wrote in message
...
> On Wed, 03 Dec 2003 13:08:30 +0000, Shaun Rimmer wrote:
>
> >> Don't got any gears to change ;-P
> >
> > Yes - it's still 'gearing' dude - gears are what set the ratio.
>
> Perhaps you missed it, but Bill's now given up on the whole new-fangled
> 'gear' thing and gone back to *true* riding. He's now got a hobby
> horse.

Heheheheh!

"Two little boys had two little toys,"

',;~}~



Shaun aRe

[John Morgan]

> >> Perhaps you missed it, but Bill's now given up on the whole new-fangled
> >> 'gear' thing and gone back to *true* riding. He's now got a hobby
> >> horse.
> >>
> >
> > No ****ing Gears!
> >
> >
http://www.sciencetech.technomuses.ca/english/collection/images/litho.jpg
>
> Yep, that's a hobby horse...

Another thread hijacked, another day's pay for the ol' AMB crew.

-John Morgan

[Bill Wheeler]

On Tue, 2 Dec 2003 23:32:32 -0500, "Michael Dart" >
wrote:

>Mike - free your mind and your ass will follow.
>
Nice
....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...