When I get stuck with something I usually take a rest and go YouTube surfing. The universe then has a unique way in showing you what you need. Some years ago I saw this video:
https://www.youtube.com/watch?v=jyQwgBAaBag&t=14sDerek from Veritasium has a Phd in physics his videos also go through rigorous scientific validation, he wont upload or claim anything that didn't go through rigorous scientific validation. I respect Derek as he does not let his education or bias get in the way, but most importantly I love him because his videos are a great example on how science education should be done.
So what is special about Blackbird? Well, given an initial push, it keeps
accelerating with or against the wind direction (which does not matter) and keeps doing so until the pilot hits the breaks or something breaks. Seemingly gaining kinetic energy out of nowhere. But how can that be? Isn't that like trying to fly by pulling on the straps of your boots? Against newtons third law, against the 2nd law of thermodynamics, so many laws broken!
Well something everybody seemed to have missed besides its creators is the interplay of two things. Rigid body dynamics and
constraints. Derek calls it "mechanical advantage" in the video but that is not completely true. There is more going on that just a
linear lever effect which just trades distance for force.
First you have the propeller generating a forward force because it is forced by the wheels to do so. Then you have the wheels which can somehow overcome the counter-torque that comes from this and rolls forward. It is not ONLY a lever effect or mechanical advantage as in both cases the back torque of the propeller will be greater than that of the wheels and blackbird would get nowhere. I did the analysis I encourage you to do the same.
The real answer is rigid body dynamics and constraints.
Take a rigid body floating in space problem. Given a force acting on any point of the rigid body:
We want to know how it will behave. If you were paying attention in class you know to apply the following two rules:
- Take the force an apply it on the CoM of the body
- Decompose the force at the point of action, so it becomes perpendicular to the distance vector from the CoM. And use this as a force couple to calculate the torque on the body.
Using these two rules we get:
If the moment of inertia, or rotational mass as I would like to call, it is also defined we can fully define the motion of said rigid body and the rigid body starts to rotate CW as it moves in the direction of the force. So far so good, nothing new or special.
However lets introduce something new, something we call earth. Lets leave space and take our rigid body with us back to earth. On earth we have something new to play with called "constraints", a magical ability to link masses together and constrain their positions and rotations.
Lets add a first constraint point and apply the same force:
It doesn't take a genius to see that the body would rotate CW. The same direction as it rotated in space.
Now lets use our freedom on earth to relocate the constraint point and see what happens:
Would you look at that, the same force but the rotation direction has changed just by changing the location of the constraint point. We can freely choose how the torque acts while its linear "component" remains in the same direction. A pretty cool feature if you ask me.
This is the true secret of Blackbird and any OU effect.
It took me a few months to figure out why I saw OU effects in FEMM, the path was long and painful. But I am sure you are much smarter than me and will grasp the significance of this quicker.
Without gravity and friction, these constraints are not possible. Constraints are the diodes of the universe we choose in which direction to point them. The universe has given us lego blocks to play with in the form of mass and how to constrain and structure them. Our imagination is the only limit. We have arguably only used the positive side of friction so far but friction also comes in a "negative" flavor, allowing us to direct the immense potential energies found in earths gravity OR in its rotation OR in magnets, etc etc... and turn it into vast amounts of linear kinetic energy. And the key lies in how rotation is being constrained, whether it is the domains of ferromagnetic materials or gravity its all the same because it IS the same force on all scales. A line and a circle, or what physicists call a particle and field. Friction, the power to constrain them and let them interact is the so called "theory of everything". A force glossed over so quickly and taken for granted that students dont even have the time to wonder how it does what it does.
For some, even this explanation will not be satisfactory. They will "believe it when they see it". However all around us are processes we dont see, yet each and everyone is keeping us alive, so they are not real either? This ridiculous notion comes from materialistic based minds that grabbed on hard matter 100 years ago and never let go. Past scientists were not like this, they explored the visible and invisible. Philosophy was a great part of science until it got dissected out of it and discarded as being useless.
However I found its better to believe before you see, as without imagination you get nowhere. I am also done asking myself how 100 years of science could have missed such a simple and fundamental property of nature as even posting this takes time and energy which I rather could have spent on building and sharing cool ideas. But here we are, first having to go through the many walls of mans ego, before he can accept fault and move on with his life to cooperate in the new reality that is ahead.
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Topic: Blackbird and the secrets it holds. (Read 3950 times)
