Thank you to all of you who have provide tips on Pinewood Derby cars
in response to a previous post. We would like to ask a couple of
follow-up questions:
1. What is the best way to make sure that the axle slots are square to
the body of the car? We have the clear plastic tool sold at the Scout
shop that helps make the determination. However, we were not sure the
besy way to "straighten" the slots and then get the nails/axles to
follow the new line of the slot.
2. We used the dry lube sold by the Scout shop. Everyone has been
mentioning using graphite. We are only allowed to use dry
lubrication, but we can use graphite. Is that what is typically sold
in the Scout shops? In other words, do we need to look specifically
for dry graphite lube or is all of the dry lube graphite anyway?
3. How do you straighten the axles in order to make the car go
straight? When we tried to do this last year after the axles were on
the car, it seemed to be impossible to move them and have them stay in
place. Is there a good process for doing this? What are some steps
before and after the wheels are on the car?
Thanks again for your advice. We are looking forward to using all of
these tips when we build our next car.
Jim
In article <[email protected]>, J. Clarke <[email protected]> wrote:
>A little physics is a dangerous thing.
>
>Doug really should perform some experiments with actual pinewood derby
>cars before he pontificates. He is likely to find that his knowledge
>of physics has some gaps.
Care to point them out?
The friction forces are _exactly_the_same_.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
On Feb 9, 2:30 pm, "Jim" <[email protected]> wrote:
> Thank you to all of you who have provide tips on Pinewood Derby cars
> in response to a previous post. We would like to ask a couple of
> follow-up questions:
>
My answers are based on what me and my son did for his car (1st place
his Webelos division). YMMV, but it worked for us.
> 1. What is the best way to make sure that the axle slots are square to
> the body of the car? We have the clear plastic tool sold at the Scout
> shop that helps make the determination. However, we were not sure the
> besy way to "straighten" the slots and then get the nails/axles to
> follow the new line of the slot.
>
Depending on the rules you can do a couple of things. Last year we
didn't use the slots that were there but rather drilled holes in the
side with a drill press. This year, we did something a little
different. We filled in the slots with a filler and re-cut the slots
ourselves. We simply used a square and laid out the first axle.
Then, we very carefully measured that point ot the rear axle and laid
out and cut that axle.
> 2. We used the dry lube sold by the Scout shop. Everyone has been
> mentioning using graphite. We are only allowed to use dry
> lubrication, but we can use graphite. Is that what is typically sold
> in the Scout shops? In other words, do we need to look specifically
> for dry graphite lube or is all of the dry lube graphite anyway?
>
If it's sold by the scout shop you should be in good shape. One of
the things we did was to polish the snot out of the axles. An
additional step that someone recommended was to place your nail in a
drill press with the wheel on. Hold the wheel as the nail is spinning
and add lube to the axle while it's spinning. Apparently, that helps
to further polish out the axle and embed lube in the wheel and axle.
Seems to have worked for us.
> 3. How do you straighten the axles in order to make the car go
> straight? When we tried to do this last year after the axles were on
> the car, it seemed to be impossible to move them and have them stay in
> place. Is there a good process for doing this? What are some steps
> before and after the wheels are on the car?
>
Bruth force! Actually, if you lay it out carefully you will get a
fairly straight riding car. Any adjustments would be simply grabbing
the wheel and bend it by hand. It doesn't take much.
Just a couple other things that might make a difference. I've heard
that having 3 wheelers makes a difference. Check your rules on that
one. That is, one of your wheels simply doesn't touch the track. The
friction of three wheels is less than four. Also, on the wheels
themselves some people make the part of the wheel where the nail goes
through convex. Again, less friction. And last, again with the
wheels, people also sand back, at an angle, the portion of the wheel
that could touch the car.
> Thanks again for your advice. We are looking forward to using all of
> these tips when we build our next car.
>
> Jim
On Feb 9, 2:30 pm, "Jim" <[email protected]> wrote:
> Thank you to all of you who have provide tips onPinewoodDerbycars
> in response to a previous post. We would like to ask a couple of
> follow-up questions:
>
> 1. What is the best way to make sure that the axle slots are square to
> the body of the car? We have the clear plastic tool sold at the Scout
> shop that helps make the determination. However, we were not sure the
> besy way to "straighten" the slots and then get the nails/axles to
> follow the new line of the slot.
>
> 2. We used the dry lube sold by the Scout shop. Everyone has been
> mentioning using graphite. We are only allowed to use dry
> lubrication, but we can use graphite. Is that what is typically sold
> in the Scout shops? In other words, do we need to look specifically
> for dry graphite lube or is all of the dry lube graphite anyway?
>
> 3. How do you straighten the axles in order to make the car go
> straight? When we tried to do this last year after the axles were on
> the car, it seemed to be impossible to move them and have them stay in
> place. Is there a good process for doing this? What are some steps
> before and after the wheels are on the car?
>
> Thanks again for your advice. We are looking forward to using all of
> these tips when we build our next car.
>
> Jim
besure to see the pinewoodderby tips at the PinewoodDerbyDen.Com web
site....
On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
> In article <[email protected]>, "Geo" <[email protected]> wrote:
>
> >Just a couple other things that might make a difference. I've heard
> >that having 3 wheelers makes a difference. Check your rules on that
> >one. That is, one of your wheels simply doesn't touch the track. The
> >friction of three wheels is less than four.
>
> Incorrect -- the total friction is unchanged, because the weight supported
> remains the same. With only three wheels touching the track, the wieght on
> each wheel, and consequently the friction force on each wheel, goes up by 33%.
>
A three wheel car is faster because it takes less energy to spin three
wheels than four.
> >Also, on the wheels
> >themselves some people make the part of the wheel where the nail goes
> >through convex. Again, less friction.
>
> Again, incorrect. Changing the size or shape of the contact area does not
> change the amount of friction.
Moving the friction point closer to the axle reduces the torque on the
wheel.
>
> --
> Regards,
> Doug Miller (alphageek at milmac dot com)
>
> It's time to throw all their damned tea in the harbor again.
On Feb 9, 6:04 pm, Bill in Detroit <[email protected]> wrote:
> Jim wrote:
> > 2. We used the dry lube sold by the Scout shop. Everyone has been
> > mentioning using graphite. We are only allowed to use dry
> > lubrication, but we can use graphite. Is that what is typically sold
> > in the Scout shops? In other words, do we need to look specifically
> > for dry graphite lube or is all of the dry lube graphite anyway?
>
> When I worked at Delta Research in Livonia, MI we sometimes used
> molybdenum powder (molybdenum di-sulfide? I'm not certain of the exact
> name -- nearly 15 years since I used it). I was told at the time that it
> was much more slippery than graphite because it is shaped like little
> teeny-tiny ball bearings.
>
> And it's very, very dry.
>
You can get graphite with molybdenum and it really makes a difference
over plain graphite. We timed our wheels and they all spun at least 5
seconds longer with the molydbenum lube.
http://www.a2zhobbies.com/PineCar/Accessories/PIN-P358.html
> Bill
> --
> Make yourself an honest man, and then you may be sure that there is one
> rascal less in the world.
> Thomas Carlyle (1795 - 1881)http://nmwoodworks.com
>
> ---
> avast! Antivirus: Outbound message clean.
> Virus Database (VPS): 000712-2, 02/09/2007
> Tested on: 2/9/2007 8:04:11 PM
> avast! - copyright (c) 1988-2007 ALWIL Software.http://www.avast.com
On Feb 10, 2:03 pm, [email protected] (Doug Miller) wrote:
> In article <[email protected]>, Tom Watson <[email protected]> wrote:
> >On Sat, 10 Feb 2007 13:39:23 GMT, [email protected] (Doug Miller)
> >wrote:
>
> >>In article <[email protected]>,
> > "onoahimahi" <[email protected]> wrote:
> >>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
> >>>> In article <[email protected]>, "Geo"
> >>> <[email protected]> wrote:
>
> >>>> >Just a couple other things that might make a difference. I've heard
> >>>> >that having 3 wheelers makes a difference. Check your rules on that
> >>>> >one. That is, one of your wheels simply doesn't touch the track. The
> >>>> >friction of three wheels is less than four.
>
> >>>> Incorrect -- the total friction is unchanged, because the weight supported
> >>>> remains the same. With only three wheels touching the track, the wieght on
> >>>> each wheel, and consequently the friction force on each wheel, goes up by
> >>> 33%.
>
> >>>A three wheel car is faster because it takes less energy to spin three
> >>>wheels than four.
>
> >>Again, incorrect. The total energy is the same, because the total friction is
> >>the same.
>
> >>If anything, a car riding on only three wheels is likely to be somewhat
> >>slower: since the friction force will be imbalanced left-to-right, the car
> >>will travel a slightly curved path, with the two wheels on the concave side.
>
> >>>> >Also, on the wheels
> >>>> >themselves some people make the part of the wheel where the nail goes
> >>>> >through convex. Again, less friction.
>
> >>>> Again, incorrect. Changing the size or shape of the contact area does not
> >>>> change the amount of friction.
>
> >>>Moving the friction point closer to the axle reduces the torque on the
> >>>wheel.
>
> >>And that makes a difference how?
>
> >http://www.pinewoodderbyphysics.com/pdf%20files/Lecture%2011.pdf
>
> Thanks, Tom, that says pretty much exactly what I've been saying all along.
>
Again incorrect - you said above "If anything, a car riding on only
three wheels is likely to be somewhat slower" but this reference, as
well as the comments of other posters who actually know how to help
their sons build fast cars, says "raising one front wheel does
increase speed considerably"
I can speak with authority on this subject because my son's last two
cars have been superfast not only winning first place pack but going
on to win first place district. Last year at the District race, he had
three of the 5 fastest times of the day for all age groups. Further,
we got to "Support our Troops" in a small way by helping a boy whose
dad is deployed in Iraq. He came down to my shop and we helped him
build his car and he won first place in his pack. Both cars had a
lifted front wheel.
-Scott
> --
> Regards,
> Doug Miller (alphageek at milmac dot com)
>
> It's time to throw all their damned tea in the harbor again.
On Feb 10, 8:39 am, [email protected] (Doug Miller) wrote:
> In article <[email protected]>, "onoahimahi" <[email protected]> wrote:
>
> ...
>
> >Moving the friction point closer to the axle reduces thetorqueon the
> >wheel.
>
> And that makes a difference how?
>
It makes a difference in the angular acceleration of the wheel.
It's a real small difference, but if you win by half an inch, you win.
If you can lighten the wheels by removing mass nearest the hub
that will help too.
--
FF
On Feb 9, 4:39 pm, [email protected] (Doug Miller) wrote:
>
>...
>
> Again, incorrect. Changing the size or shape of the contact area does not
> change the amount of friction.
>
This is true. Yet if you want to slide a heavy object,
it helps to put it on skids, even if the object has a
flat side and it's on a hard surface. I've never been
able to figure out why.
--
FF
Jim wrote:
> 2. We used the dry lube sold by the Scout shop. Everyone has been
> mentioning using graphite. We are only allowed to use dry
> lubrication, but we can use graphite. Is that what is typically sold
> in the Scout shops? In other words, do we need to look specifically
> for dry graphite lube or is all of the dry lube graphite anyway?
When I worked at Delta Research in Livonia, MI we sometimes used
molybdenum powder (molybdenum di-sulfide? I'm not certain of the exact
name -- nearly 15 years since I used it). I was told at the time that it
was much more slippery than graphite because it is shaped like little
teeny-tiny ball bearings.
And it's very, very dry.
Bill
--
Make yourself an honest man, and then you may be sure that there is one
rascal less in the world.
Thomas Carlyle (1795 - 1881)
http://nmwoodworks.com
---
avast! Antivirus: Outbound message clean.
Virus Database (VPS): 000712-2, 02/09/2007
Tested on: 2/9/2007 8:04:11 PM
avast! - copyright (c) 1988-2007 ALWIL Software.
http://www.avast.com
On Sat, 10 Feb 2007 16:38:04 GMT, "KERRY MONTGOMERY"
<[email protected]> wrote:
>
>"Doug Miller" <[email protected]> wrote in message
>news:[email protected]...
>> In article <[email protected]>,
>> "onoahimahi" <[email protected]> wrote:
>>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>>>> In article <[email protected]>, "Geo"
>>> <[email protected]> wrote:
>>>>
>>>> >Just a couple other things that might make a difference. I've heard
>>>> >that having 3 wheelers makes a difference. Check your rules on that
>>>> >one. That is, one of your wheels simply doesn't touch the track. The
>>>> >friction of three wheels is less than four.
>>>>
>>>> Incorrect -- the total friction is unchanged, because the weight
>>>> supported
>>>> remains the same. With only three wheels touching the track, the wieght
>>>> on
>>>> each wheel, and consequently the friction force on each wheel, goes up
>>>> by
>>> 33%.
>>>>
>>>
>>>A three wheel car is faster because it takes less energy to spin three
>>>wheels than four.
>>
>> Again, incorrect. The total energy is the same, because the total friction
>> is
>> the same.
>>
>> If anything, a car riding on only three wheels is likely to be somewhat
>> slower: since the friction force will be imbalanced left-to-right, the car
>> will travel a slightly curved path, with the two wheels on the concave
>> side.
>>>
>>>> >Also, on the wheels
>>>> >themselves some people make the part of the wheel where the nail goes
>>>> >through convex. Again, less friction.
>>>>
>>>> Again, incorrect. Changing the size or shape of the contact area does
>>>> not
>>>> change the amount of friction.
>>>
>>>Moving the friction point closer to the axle reduces the torque on the
>>>wheel.
>>
>> And that makes a difference how?
>>
>> --
>> Regards,
>> Doug Miller (alphageek at milmac dot com)
>>
>> It's time to throw all their damned tea in the harbor again.
>
>Regarding 3 wheels VS 4; 3 wheels will require less energy to accelerate
>than 4, won't they?
A little physics is a dangerous thing.
Doug really should perform some experiments with actual pinewood derby
cars before he pontificates. He is likely to find that his knowledge
of physics has some gaps.
>Kerry
>
"Doug Miller" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>, "KERRY
> MONTGOMERY" <[email protected]> wrote:
>>
>>"Doug Miller" <[email protected]> wrote in message
>>news:[email protected]...
>>> In article <[email protected]>,
>>> "onoahimahi" <[email protected]> wrote:
>>>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>>>>> In article <[email protected]>,
>>>>> "Geo"
>>>> <[email protected]> wrote:
>>>>>
>>>>> >Just a couple other things that might make a difference. I've heard
>>>>> >that having 3 wheelers makes a difference. Check your rules on that
>>>>> >one. That is, one of your wheels simply doesn't touch the track.
>>>>> >The
>>>>> >friction of three wheels is less than four.
>>>>>
>>>>> Incorrect -- the total friction is unchanged, because the weight
>>>>> supported
>>>>> remains the same. With only three wheels touching the track, the
>>>>> wieght
>>>>> on
>>>>> each wheel, and consequently the friction force on each wheel, goes up
>>>>> by
>>>> 33%.
>>>>>
>>>>
>>>>A three wheel car is faster because it takes less energy to spin three
>>>>wheels than four.
>>>
>>> Again, incorrect. The total energy is the same, because the total
>>> friction
>>> is
>>> the same.
>>>
>>> If anything, a car riding on only three wheels is likely to be somewhat
>>> slower: since the friction force will be imbalanced left-to-right, the
>>> car
>>> will travel a slightly curved path, with the two wheels on the concave
>>> side.
>>>>
>>>>> >Also, on the wheels
>>>>> >themselves some people make the part of the wheel where the nail goes
>>>>> >through convex. Again, less friction.
>>>>>
>>>>> Again, incorrect. Changing the size or shape of the contact area does
>>>>> not
>>>>> change the amount of friction.
>>>>
>>>>Moving the friction point closer to the axle reduces the torque on the
>>>>wheel.
>>>
>>> And that makes a difference how?
>>>
>>> --
>>> Regards,
>>> Doug Miller (alphageek at milmac dot com)
>>>
>>> It's time to throw all their damned tea in the harbor again.
>>
>>Regarding 3 wheels VS 4; 3 wheels will require less energy to accelerate
>>than 4, won't they?
>
> Go back a few posts and see where the 3 vs. 4 discussion started. The case
> being discussed is 4 wheels with only 3 in contact with the ground, vs. 4
> wheels with all 4 in contact.
>
> The friction forces are _exactly_the_same_.
>
> --
> Regards,
> Doug Miller (alphageek at milmac dot com)
>
> It's time to throw all their damned tea in the harbor again.
Doug,
Wasn't questioning the friction forces at all. It seems that accelerating 4
wheels to the same rotational speed will take more energy than accelerating
3 wheels to the same rotational speed. Not due to friction, but due to the
rotational inertia of the wheels. Which would mean that the total energy
would not be the same, even though the total friction is the same.
Kerry
In article <[email protected]>, "Geo" <[email protected]> wrote:
>Just a couple other things that might make a difference. I've heard
>that having 3 wheelers makes a difference. Check your rules on that
>one. That is, one of your wheels simply doesn't touch the track. The
>friction of three wheels is less than four.
Incorrect -- the total friction is unchanged, because the weight supported
remains the same. With only three wheels touching the track, the wieght on
each wheel, and consequently the friction force on each wheel, goes up by 33%.
>Also, on the wheels
>themselves some people make the part of the wheel where the nail goes
>through convex. Again, less friction.
Again, incorrect. Changing the size or shape of the contact area does not
change the amount of friction.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
In article <[email protected]>, Tom Watson <[email protected]> wrote:
>On Sat, 10 Feb 2007 13:39:23 GMT, [email protected] (Doug Miller)
>wrote:
>
>>In article <[email protected]>,
> "onoahimahi" <[email protected]> wrote:
>>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>>>> In article <[email protected]>, "Geo"
>>> <[email protected]> wrote:
>>>>
>>>> >Just a couple other things that might make a difference. I've heard
>>>> >that having 3 wheelers makes a difference. Check your rules on that
>>>> >one. That is, one of your wheels simply doesn't touch the track. The
>>>> >friction of three wheels is less than four.
>>>>
>>>> Incorrect -- the total friction is unchanged, because the weight supported
>>>> remains the same. With only three wheels touching the track, the wieght on
>>>> each wheel, and consequently the friction force on each wheel, goes up by
>>> 33%.
>>>>
>>>
>>>A three wheel car is faster because it takes less energy to spin three
>>>wheels than four.
>>
>>Again, incorrect. The total energy is the same, because the total friction is
>>the same.
>>
>>If anything, a car riding on only three wheels is likely to be somewhat
>>slower: since the friction force will be imbalanced left-to-right, the car
>>will travel a slightly curved path, with the two wheels on the concave side.
>>>
>>>> >Also, on the wheels
>>>> >themselves some people make the part of the wheel where the nail goes
>>>> >through convex. Again, less friction.
>>>>
>>>> Again, incorrect. Changing the size or shape of the contact area does not
>>>> change the amount of friction.
>>>
>>>Moving the friction point closer to the axle reduces the torque on the
>>>wheel.
>>
>>And that makes a difference how?
>
>
>http://www.pinewoodderbyphysics.com/pdf%20files/Lecture%2011.pdf
Thanks, Tom, that says pretty much exactly what I've been saying all along.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
"Doug Miller" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> "onoahimahi" <[email protected]> wrote:
>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>>> In article <[email protected]>, "Geo"
>> <[email protected]> wrote:
>>>
>>> >Just a couple other things that might make a difference. I've heard
>>> >that having 3 wheelers makes a difference. Check your rules on that
>>> >one. That is, one of your wheels simply doesn't touch the track. The
>>> >friction of three wheels is less than four.
>>>
>>> Incorrect -- the total friction is unchanged, because the weight
>>> supported
>>> remains the same. With only three wheels touching the track, the wieght
>>> on
>>> each wheel, and consequently the friction force on each wheel, goes up
>>> by
>> 33%.
>>>
>>
>>A three wheel car is faster because it takes less energy to spin three
>>wheels than four.
>
> Again, incorrect. The total energy is the same, because the total friction
> is
> the same.
>
> If anything, a car riding on only three wheels is likely to be somewhat
> slower: since the friction force will be imbalanced left-to-right, the car
> will travel a slightly curved path, with the two wheels on the concave
> side.
>>
>>> >Also, on the wheels
>>> >themselves some people make the part of the wheel where the nail goes
>>> >through convex. Again, less friction.
>>>
>>> Again, incorrect. Changing the size or shape of the contact area does
>>> not
>>> change the amount of friction.
>>
>>Moving the friction point closer to the axle reduces the torque on the
>>wheel.
>
> And that makes a difference how?
>
> --
> Regards,
> Doug Miller (alphageek at milmac dot com)
>
> It's time to throw all their damned tea in the harbor again.
Regarding 3 wheels VS 4; 3 wheels will require less energy to accelerate
than 4, won't they?
Kerry
In article <[email protected]>, "onoahimahi" <[email protected]> wrote:
>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>> In article <[email protected]>, "Geo"
> <[email protected]> wrote:
>>
>> >Just a couple other things that might make a difference. I've heard
>> >that having 3 wheelers makes a difference. Check your rules on that
>> >one. That is, one of your wheels simply doesn't touch the track. The
>> >friction of three wheels is less than four.
>>
>> Incorrect -- the total friction is unchanged, because the weight supported
>> remains the same. With only three wheels touching the track, the wieght on
>> each wheel, and consequently the friction force on each wheel, goes up by
> 33%.
>>
>
>A three wheel car is faster because it takes less energy to spin three
>wheels than four.
Again, incorrect. The total energy is the same, because the total friction is
the same.
If anything, a car riding on only three wheels is likely to be somewhat
slower: since the friction force will be imbalanced left-to-right, the car
will travel a slightly curved path, with the two wheels on the concave side.
>
>> >Also, on the wheels
>> >themselves some people make the part of the wheel where the nail goes
>> >through convex. Again, less friction.
>>
>> Again, incorrect. Changing the size or shape of the contact area does not
>> change the amount of friction.
>
>Moving the friction point closer to the axle reduces the torque on the
>wheel.
And that makes a difference how?
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
In article <[email protected]>, "KERRY MONTGOMERY" <[email protected]> wrote:
>
>"Doug Miller" <[email protected]> wrote in message
>news:[email protected]...
>> In article <[email protected]>,
>> "onoahimahi" <[email protected]> wrote:
>>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>>>> In article <[email protected]>, "Geo"
>>> <[email protected]> wrote:
>>>>
>>>> >Just a couple other things that might make a difference. I've heard
>>>> >that having 3 wheelers makes a difference. Check your rules on that
>>>> >one. That is, one of your wheels simply doesn't touch the track. The
>>>> >friction of three wheels is less than four.
>>>>
>>>> Incorrect -- the total friction is unchanged, because the weight
>>>> supported
>>>> remains the same. With only three wheels touching the track, the wieght
>>>> on
>>>> each wheel, and consequently the friction force on each wheel, goes up
>>>> by
>>> 33%.
>>>>
>>>
>>>A three wheel car is faster because it takes less energy to spin three
>>>wheels than four.
>>
>> Again, incorrect. The total energy is the same, because the total friction
>> is
>> the same.
>>
>> If anything, a car riding on only three wheels is likely to be somewhat
>> slower: since the friction force will be imbalanced left-to-right, the car
>> will travel a slightly curved path, with the two wheels on the concave
>> side.
>>>
>>>> >Also, on the wheels
>>>> >themselves some people make the part of the wheel where the nail goes
>>>> >through convex. Again, less friction.
>>>>
>>>> Again, incorrect. Changing the size or shape of the contact area does
>>>> not
>>>> change the amount of friction.
>>>
>>>Moving the friction point closer to the axle reduces the torque on the
>>>wheel.
>>
>> And that makes a difference how?
>>
>> --
>> Regards,
>> Doug Miller (alphageek at milmac dot com)
>>
>> It's time to throw all their damned tea in the harbor again.
>
>Regarding 3 wheels VS 4; 3 wheels will require less energy to accelerate
>than 4, won't they?
Go back a few posts and see where the 3 vs. 4 discussion started. The case
being discussed is 4 wheels with only 3 in contact with the ground, vs. 4
wheels with all 4 in contact.
The friction forces are _exactly_the_same_.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
On Sat, 10 Feb 2007 13:39:23 GMT, [email protected] (Doug Miller)
wrote:
>In article <[email protected]>, "onoahimahi" <[email protected]> wrote:
>>On Feb 9, 2:39 pm, [email protected] (Doug Miller) wrote:
>>> In article <[email protected]>, "Geo"
>> <[email protected]> wrote:
>>>
>>> >Just a couple other things that might make a difference. I've heard
>>> >that having 3 wheelers makes a difference. Check your rules on that
>>> >one. That is, one of your wheels simply doesn't touch the track. The
>>> >friction of three wheels is less than four.
>>>
>>> Incorrect -- the total friction is unchanged, because the weight supported
>>> remains the same. With only three wheels touching the track, the wieght on
>>> each wheel, and consequently the friction force on each wheel, goes up by
>> 33%.
>>>
>>
>>A three wheel car is faster because it takes less energy to spin three
>>wheels than four.
>
>Again, incorrect. The total energy is the same, because the total friction is
>the same.
>
>If anything, a car riding on only three wheels is likely to be somewhat
>slower: since the friction force will be imbalanced left-to-right, the car
>will travel a slightly curved path, with the two wheels on the concave side.
>>
>>> >Also, on the wheels
>>> >themselves some people make the part of the wheel where the nail goes
>>> >through convex. Again, less friction.
>>>
>>> Again, incorrect. Changing the size or shape of the contact area does not
>>> change the amount of friction.
>>
>>Moving the friction point closer to the axle reduces the torque on the
>>wheel.
>
>And that makes a difference how?
http://www.pinewoodderbyphysics.com/pdf%20files/Lecture%2011.pdf
Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1/
In article <[email protected]>, "KERRY MONTGOMERY" <[email protected]> wrote:
>Doug,
>Wasn't questioning the friction forces at all. It seems that accelerating 4
>wheels to the same rotational speed will take more energy than accelerating
>3 wheels to the same rotational speed. Not due to friction, but due to the
>rotational inertia of the wheels. Which would mean that the total energy
>would not be the same, even though the total friction is the same.
Perhaps -- but the mass of one wheel is very small in relation to the mass of
the body of the car, and the radius is only about 15mm, so the moment of
inertia of the wheel is negligible. Any gain achieved in this manner is, I
suspect, likely to be more than offset by the fact that the unbalanced
geometry will cause the car to deviate from a straight line.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.