For example, it would take the same force to move a heavy table
across a wooden floor if the table was on its side or if the table
was on its legs, provided the coefficient of friction was the same.
This is Why
You already know that when 2 objects rub against
each other, friction is created in the form of Heat. Friction is
something we want to eliminate or reduce as much as possible in
pinewood racing. Once your car hits the flat track, a car with more
friction will slow down quickly and other pinewood cars will pass
it up before it reaches the finish line.
The Friction is caused by the roughness of the surfaces of the 2
objects, in this case the axel and the wheel. And in related but
slighty different case, the wheel rubbing against the pinewood car
body. It's also caused by molecular attraction between the 2 surfaces
(although this is the smallest form of friction we will deal with,
it stil is something to think about)
To begin with, viewed under a microscope or magnifying glass, the
axes and wheels of your pinewood derby car will look--- let just
say 'not very smooth'. The Rougher the 2 surfaces, the more friction.
The Slower your pinewood car will go.
You would think that there is more friction when the surfaces are
But the friction law states otherwise.
It's important for Pinewood enthusiasts to know that The amount
of Friction is Independent of the amount of surface areas
being 'rubbed together'.
Huh? It's true, Friction is a tricky, tricky adversary! And that's
one of the hundreds of Reasons why we made a Pinewood Speed Secrets
OK, Alright! So you have 2 types of friction.. So what?? Just polish
it up, add some graphite and be done with it!
Not so Fast there "Racer X" Now that you know what Friction is...
Let's look at what we can do About IT.
There are 2 Types of Friction we are concerned with.
Static Friction= The Resistance TO motion when an object
is not moving Lets think about the table again, When you first try
and move it, The heavy table seems to be "glued in place" and much
effort is required to overcome the inertia of this heavy object.
This "Static" Friction is caused by a combination of the resistance
due to the roughness of the surfaces and the molecular attractions
trying to hold the surfaces together.
Kinetic Friction= Sliding Friction of a moving object Once
you get the table Moving, the amount of friction is less than when
it was standing still. Sliding friction is a form of kinetic friction.
Most of the friction is cause by the roughness of the two surfaces.
First of all, Polishing your axels is a must - But you need to
actually SEE what your doing, so I recommend you get a Magnifying
glass or a 16x jewlers loop. Then, you can see the changes you are
making AS you make them.
Wait a minute! You Just said "The amount of Friction is Independent
of the amount of surface areas being 'rubbed together."
Yes I did, and that's one of those LAWS we need to 'work around
|Now that we know what friction is,
and that there are two types we need to be concerned with in
pinewood racing, We can examine how to reduce the friction and
set our sights on KEEPING THE ENERGY instead of letting
FRICTION TAKE IT AWAY! Energy you will recall, that we gained
by Designing our pinewood derby body and properly weighting
it, Energy you will see at work, when your pinewood car pulls
away from the others on the Flat portion of the racetrack! Energy
that Friction cannot get it's ugly hands on because we are going
to 'outsmart it'. ok so here we go..
Once your pinewood racer hits the flat track, it can no longer
gain any speed. It can only Lose speed. This Loss is due
to Friction. A close look at the wheels, axels and body will allow
you to understand there are several areas in which friction can
influence your pinewood racer. That right, several unique areas,
not just one. By looking at each area and deciding the best way
to reduce the friction in that particular area, you will be helping
your pinewood car to maintain it's speed during it's flat track
run towards the finish line. The best way to reduce the influence
of friction is to ELIMINATE IT!
I beleive you will WIN this Year !!
You see, We need to REDUCE the Probablility of Friction by ELIMINATING
surface material. The Smaller the Friction surface, the Less
Probability that your axel surfaces, wheel surfaces etc.
will be "messing up" the friction equation with uneven surface preparation,
dimensions and other irregularities. I have always figured that
since the 'Coefficient of Friction - u ' (Fr = u x W) is the ONE
variable which you can impact directly. It's best to concentrate
on keeping that variable from 'VARYING' too much.. CRAZY you say?
Maybe, But I'll let YOU be the judge... Read on..
Yet another wonderful result of friction is maximum velocity -
where the drag force equals the driving force. This final, constant
velocity of motion is called a "terminal velocity",
we show you an inside look at how many actual friction surfaces
there are and give you ways, other than just using graphite to reduce
friction. Everyone will be using graphite or another lubricant so
since you want the fastest car possible, you need to take it a step
you can see the largest friction area is the axle shaft itself, the
other area we can work on is the inner nail head. Since the axle shaft
is the largest contributor to friction due to the it's surface area,
The probability of irregularities varying the 'coefficient of friction'
on each subsequent revolution of the wheel makes it an ideal candidate
for minor (for begninner pinewood racers) or major (advanced pinewood
Basic Axel tips
look at your axles and find the small raised grooves. Now because
these are ďNAILSĒ and not perfectly machined axles, they are not really
round and also have all sorts of imperfections due to the process
of making the nails. I go back to my Probability of Friction Theory
here. There's just no way to get the Coefficent of friction constant
with all that surface area But since thatís all we have to work with,
You can just do the best you can. We have found that the Small raised
grooves are the High Spot on the Axle. So lets get rid of those first.
grooves must face up when you install the axles on the car. Gravity
in general will be forcing the axles (which support the weight of
the body) downward onto the wheels and by facing these grooves upwards,
we can essentially eliminate them from the friction equation. Make
sure you mark your nail head with paint to indicate where the grooves,
and this oblong area is on the axle. You are doing this for future
reference so when you install the axles later, you will know how to
orient your axles after working on them. Now just to be sure they
donít end up rubbing or throwing off your alignment File down the
grooves by hand, and only file the grooves
Check your progress with a magnifying glass or a jewelers loop.
You want it to be as perfect a possible. And Remember, the "other
guys" are probably messing up their axels because they dont know
not to do it! So when their cars wiggle and bang off the sides of
the racetrack, your pinewood car will blow right past 'em!
NOT USE a dremel or a power tool to sand down your axels! You just
need to get rid of the grooves.If you use a power tool to do this,
you will remove too much of the axel material. There isnt really enough
to begin with for perfect tuning of your pinewood car so if you reduce
the diameter of the axle at all - You will not be able to align your
car for optimum performance!.. More on that super-important subject
is available on the DVD but . for now, just file the grooves smooth
Why BY HAND?
INNER Nail head of each of your pinewood derby axels needs to be filed
too. As you can see in the picture, there is a Pinch mark left from
the nail-making process which Must be eliminated! Have an adult help
you with power tools. Chuck the axle in the drill press and file down
the pinched metal first flat, then the inner nail head at a 45-degree
angle.. You can also use a dremel or a hand drill by mounting them
in a vise and using a similar technique. Using a fine file at a 45
degree will bevel the inner nail head and reduce a particular type
of friction called torque braking Ė at least on the inner nail
Now keep in mind that you should check your pinewood racing rules
before modification of the axels or wheels. Most will allow you
to debur and polish
Go slowly and again, use the jewelers loop to inspect your progress.
You will be able to spot imperfections and correct them quickly.
Remember the paint mark must face up when you install your axles
so if you start to accidentally rub it away, repaint it.
Our Friction section combines the Basics of Friction Reduction
for beginners as well as Full-on axel and wheel modification for
advanced pinewood derby racers. It's definately one of the most
informative documentations you will see on the subject, For Beginners
and Advanced Pinewood Racers - everyone can learn something. So
when you get a chance, pick up a copy of our NEW DVD..
Finally polish your pinewood axel by using the basic polishing
techniques shown on the DVD. Finish up by using the CLOTH side of
an EMERY sheet. Donít use the abrasive side which will change
the diameter of the axel and you wont be able to align your car
with enough precision to win all your pinewood races. The cloth
side will buff the metal to a mirror shine. Be sure to inspect with
the jewelers loupe and inspect both the inner nail head and the
Now Let's take a look at AXEL Modification
Of course, We have a entire section devoted to Reducing Friction
in your Pinewood Racer because IT's So Important! - CGI allows us
to take an inside look at the wheel/ axel combination allowing you
to see into the friction areas
Areas you may overlook. Step by step you will learn how to reduce
friction in your pinewood derby car and you will be able to conduct
your own friction test to show the progress you have made which
ultimately makes your pinewood car much faster