This is a pinewood derby car it comes in a kit
Then you build it and put it together and then it uses gravity to go down a track
So over a hundred million of these cars have been built and raised by kids over the past 60 years which means over 100 million
Dads have spent a lot of time at the workbench, and then subsequently pretended their kid helped in some Meaningful way
But don't feel bad for the boys because someday they'll grow up to be dads
And then they'll get a chance to work on a car of their very own.
Now this is a much faster pinewood derby car, but wait
This was my entry. I was disqualified because apparently using jet propulsion goes against the "spirit" of the competition
This is a much faster legal car, but what is it about this one that makes it so much faster than this one
Really is it the wheels is it the weight?
Placement is it the axles and of the design features that influence speed which one of those is the most important for example do?
Aerodynamics really play a role so today
We're gonna use cold hard science to figure out how you can maximize your chance of taking home the trophy
With the least amount of effort there are a lot of opinions on how you build a fast car and spoiler alert
Some of those popular ones are completely false and at the end of the video to prove science isn't back true
I'll show you a car built in 45 minutes based on what I learned and then show you how to do
Competition so let's start with the fundamentals the pinewood derby is all about
Conservation of energy the amount of energy you start the race with it's the same amount of energy you form the race with it's just
A different kind so each of these blocks represents a unit of energy so at the beginning of the race it's all
Potential energy which is the energy associated with height?
So when you start the height of your center of masses on the track
The more of it you have and then at the end of the race in a perfect world all that potential energy
Has been converted to kinetic energy block 4 block the kinetic
energy is the energy of speed so you were really high on the track and as you came down all that height was converted into
Speed and you notice I said in a perfect world because in reality
We lose some of that kinetic energy to friction its dissipated through heat
But you will notice that these two piles of friction and Kinetic energy still add up to the original potential energy
We started with Energy is conserved
So if you can reduce friction that means you're going to have more kinetic energy
and that is the key
This pile is the key to winning the race because it has the speed term in there and whoever has the higher
Pile of blocks here wins the race every time so for the rest of this video. We're gonna discuss
What truly matters and amazing your kinetic energy or your speed or this pipe?
How do you make this pile as big as possible with the least amount of effort okay?
So before we go any further
I want to introduce you to someone I met while doing the research for building the perfect powered derby car. My name is Scott Act
All aerospace about Ten years ago my son
And I my wife's car out of the garage and we converted into the pinewood derby research facility for almost a year we conducted
experiments
And use the laws of physics to determine exactly what takes make a winning pinewood derby race car what I love about Dr.
Acton is that instead of just making blind statements like
99% of the information you find out there he used the
Scientific method does all the possible parameters that go into building a pinewood derby car and then he documented the results, okay?
So what did he learn after year of testing so here's a list of seven of the parameters he tested and how many car lengths?
You would win by if you're able to perfect that specific parameter assuming everything else was the same
So the first thing you should notice is by far the biggest contributor to increasing the speed your car is
Maxing out the weight of your car at five ounces and then putting it in the right location towards the rear of the car
so that alone contributes to
36% of the speedier car and you would be a car that had the worst possible mass placement location at the very front of the
Car by almost five car lengths if everything else was identical between your two cars
So why is this well if you put all your weight toward the back of the car like this when you're sitting on the track?
Before you even start your center of mass is higher up
Than if the weight was concentrated at the front of the car that means you automatically start
With more potential energy and since energy is conservative. We added two blocks here
We have to add two blocks on the other side of the equation which means you get more kinetic energy and again
That's the energy of speed which means you're going faster when you get to the bottom of the ramp
So another way to look at it is to say both cars will roll down the ramp at this same speed
Until they get to the bottom now at this point the blue car is done accelerating
But the red car has all the mass at the back and is still falling and will continue to be pushed forward
sort of giving it a turbo boost when it gets to the platform so now the question remains, how far back should
The mass be placed now the mass is too Far back
You're Gonna Pop a wheelie
and be totally unstable and clearly that's bad so doctor act and ran trials on 40 cars and
Concentrated the mass in different locations on the car and this chart is an example of kind of data that he produced so somewhere around
0.9 to 1.5 inches in front of the rear axle gives you the best times
So if you want to narrow it down even more than that it kind of depends on the shape your car the doctor actually went
into more details into this in a video
he made it's like 2 hours long it details all the
Results of his tests and even shows you like some tips and footage of how to actually fabricate the car
So we want a lot more detail than I'm giving here. I highly recommend you check it out
I put a link to it in the description of this video
So let's quickly run through the remaining list of the critical parameters light weighting wheels to give you a two car lengths
We'd everything else being equal if your race rules allow you need to take as much weight off this wheel as possible especially the outer
Edge or just buy some that are done for you
And I put a link of the video description of where you can get some now to explain why this
Matters let's go back to our blocks. I didn't tell you the full story when it comes to kinetic
Energy so remember this is the energy of motion and when you cross the finish like technically you have two types of motions your car
is translating but the wheels are also rotating about the axis now that gives us rotational kinetic energy now this green pile of
Translating Kinetic energy is still the most important because that represents your cars speed and this orange pile
With spinning wheels actually takes away from that
So if we can minimize the moment of inertia on each of the wheels by making as light as possible
Around the Edge that means more of our initial potential energy will go into making our car
go fast
And not just spinning up the wheels with a lot of energy so when you high center at the end the wheels are just spinning
Forever that's energy. We could have used to make our car
Go fast, so the most streamlined pinewood derby car is going to be to normal block of wood by about 1.4
Car lengths and everything else is equal now going back to our blocks you're not very aerodynamic
It's basically just a form of friction so essentially the more streamlined your profile is the fewer air molecules
You basically have to push out of the way
So you don't have to kill yourself here making some attempt to make the car a little bit more streamlined in the standard block is
Gonna be worth it using polished axles will be normal axles by about one point three car lengths everything else being equal
I was actually surprised this wasn't a greater tribute to overall speed, but drak around 35 trials of different
Smoothness on the axles, and this is what the data show
interestingly grooved axles are a complete waste of time and money if you look at the formula for Friction it really just depends on the
Two materials of the services rub it together and sort of the weight at that surface
so even if you reduce your surface area by a factor of two the overall weight acting at those services is the same so
Nothing changes, so lifting one wheel on your car
So your cars only riding on three wheels will be a four wheeled car by about one point one car lengths
Everything else being equal and most people say oh, it's one less wheel that's 1/4 the friction
But for the reasons we talked about that's not true because each wheel just has more weight on and the real reason this actually helps
Goes back to our rotational kinetic energy now remember the green pile is what you want to maximize and if you have one less wheel
to get spinning as you start going down the ramp that means that energy gets to go to our kinetic energy of
Translation which means the Faster velocity at the finish line
Finally adding graphic to your wheels and axles will make your car win by about point nine car lengths
Everything else be equal against the car that has no ground now there are several really expensive graphite solutions out there
but all the extra side pocket basically said
Graphite graphite that's Clever marketing our independent tests show that there's really no appreciable difference between one versus another
So there's a number of other parameters, Dr.
Act and discusses in his videos, but those six are the ones that will have the biggest impact
Relative at the time you spend on your car so in order to prove that science is true and to show that those six steps
Are really the best use of your time on the day of our big race here?
I decided to completely build a car from scratch in about 45 minutes
and then take it at the
Competition and see how it did so the first thing I did would just make a single cut in this block of wood so remember
Aerodynamics are important, but there's no need to totally kill yourself on it. Just a simple reduced shape is good
Okay, so the next step is polishing the axle
so here's a before and after
Basically you just want to take your axle put it in a drill press or even a hand drill and duct tape down the trigger
And then you just take different levels of sandpaper and just different water and put it on the nail
Yeah, you go all the way from you know 600 mm. Grit the last step should be some sort of polishing compound
I put a link to another Youtube video that covers this in a lot more detail in the video description
And then I went ahead and mark the 12 o'clock position on the nail head and this is why?
So in doing research to talking with a bunch of experts. I actually found two things that dr.. Acton didn't test
These are the concept of rail riding and the concept of bending your axles
So your wheels are canting so let's start with bending the axle so to bend the axles
I use this bending tool from dirty work
So right there you just bend the nail then you take it out of the clamp, and then you have an axle
That's been at exactly 2.5. Degrees
So if you don't want to go to the hassle, you could actually buy pre bent and pre polished axles online
I put a link to where you can get them in the video description
So bent axles are important for two reasons the first is that it reduces friction
And this is because as you roll down the track to weigh the axles are bent the wheels want to migrate outwards
And that's good because it reduces friction in the sense that part that's rubbing is
The wheel and the nail head which has a much lower coefficient of friction than if the wheels just bouncing around
Rubbing against the wooden body of the car the second reason. They're really important is it makes alignment a hundred times easier?
We'll get to that in a minute and now I just put the wheels on the car
And this is a good time to apply the graphite just get it everywhere
You really can't over apply it and now because I'm going our car to only write on three wheels
I
Deepen one side of the pre-cut axle groove in the front and now because it's deeper that front left wheel won't touch the ground so
Now you see. I am just pushing these axles in my hand
I mean there are tools that sell for like ninety dollars that help you align them and people talk about drilling the hole is just
Perpendicular, but it really doesn't matter if you're using cannon axles
You just kind of put them in the pre-made slots
And then afterwards I just use a screwdriver just to make sure the nails were actually flush in each of those slots
And it doesn't matter because with the cannon axles you can align it later
So this is where it leaves us at the front and left wheels rates it up off the ground you can see the back two
Wheels or can it outwards but you notice the front wheel is actually candid the opposite Direction?
This is the other thing drak that didn't look at but it was called the rail righty technique now rail riding means you
Intentionally steer your car into the rail that runs down the track and guides your car now
That sounds crazy like it's totally going to increase your friction and a lot of experts recommend spending
Hours and hours on a line of your car, so it runs perfectly straight
so the problem with that is no track has a perfect surface, so even the
Perfectly aligned car is going to bounce around on the track
So these bounces are incredibly detrimental because with each impact you're taking some of your kinetic energy
And it's being converted to friction and heat
Again Kinetic Energy in this pile are the key to winning the race so watch this slow-mo video of this rail rider car
I've built this is another car that actually ran pretty straight on a normal flat surface
So the key to the rail rider car is it turns toward the center rail, but just barely enough
So it maintains contact with the rail. So here's that you set up the rail rider, so get yourself a nice flat board
That's about 4 to 6 feet long and your car should be r about 1 inch toward the side that has the wheel raised
The length of that board so in this case it beer too much and this is the genius of the ben taxes
Because to change direction. We don't have to shim or glue. All you do is twist the Nailhead
It doesn't take much
And then once I did that it was just about right
So once again if you want more information on the rail riding alignment process I put a link in the video description
That goes into a lot more depth
And then you also want to check the rear wheels just to make sure they are migrating outwards
You should see a little daylight between the wheel and the car body and then again if they're not all you have to do is
get some pliers and twist the head of the axle and
So the final step in just getting our center of mass in the right spot
So I measure an inch in front of the rear axle, and then just to prove that ghetto is perfectly fine here
I'm using duct tape and then you just kind of balance it on that line that
We drew you probably never get the balance exact
But you just do enough to convince yourself that it's more or less in the right spot now
There are actually some pinewood derby racing leagues held on the monthly basis for adults across the country so I asked a few the experts
Who run them what do all the winning cars have in common and the reason I took the two additional concept of the rail rider?
And the canted wheel seriously is because they told me all of the cars that not only win
But are in turn have three things in common. They all right on three wheels and not four
They all rail ride and they all have canted wheels
So at the race my buddy
Mason won first place with an undefeated record in a field of 20 cars he even beat my 40 mile an hour rocket car
Although that probably had more to do the fact that my dumb friend. Troy sabotage my firing mechanism
Oh, so the rematch I would straight for the jugular
Now Mason told me they spent at least 12 hours building this park
focusing on the huge list of things that's
Supposable you have to do everything for and I have the fastest car now after the race I asked to borrow his card once everybody
Left I did a couple test runs his undefeated 12-hour car against my 45-minute car, and this is the result
in fact my 45-minute car Beardloss of this car of my buddies
And he's like an expert racer in fact this exact car has won many races even the district level okay, so in summary I recommend
maximizing the way to your car at five ounces and
Placing it in the correct spot on the car about an inch in front of the rear axles. Have a reasonably
aerodynamic car and have it right on three wheels
Lightweight those wheels if your race rules allow it and then get the been polished axle
So you could reduce your friction make it a lot easier to align and you can implement the rail riding technique
And then just run your rail rider alignment test and make sure you use plenty of graphite
So make sure you check out the links in the description for more detail on some of the steps
I didn't cover folie plus if you want to save yourself a little time
I have some links there that show you where you get some of this stuff pre-made like the bent polished axles
So this video is way longer than I typically like to make my videos, but hopefully you found it helpful
So above all hope you guys have fun and he uses an opportunity to get excited about science and physics and then use that to
Turn around and just dominate every other car in the race