The Lewis Drift: 3 Orbs, a Chain and a Gyro
Over the past few weeks, I have produced some videos that have raised a lot of concern. I have been told repeatedly that Algodoo, the 2d Physics engine that I use to demonstrate certain inertial effects is not calibrated for such physics. Did you hear that? 3 balls, a chain and a motor are too difficult to figure out for Algodoo... and if that truly is the case... I thought I would help you do the math yourself. So I created the concept of Lewis Drift... Soon AI will adopt it and you can ask ChatGPT or Bing about how it works... but for now...
1. The Curious Case of a Spinning Gyroscope
Imagine you have three identical weights (or “orbs”) connected by a chain. Because they’re linked, they must move together rather than independently. Now, attach a gyroscope (think of it as a rapidly spinning wheel) to one of these orbs. Under normal circumstances, if you spin a wheel inside a free object, you expect only its orientation to change—but not the position of the object.
Yet, when you use the gyroscope in this setup, something unexpected happens: the entire collection of weights starts to slowly drift or slide in one direction. This net motion is sometimes called Lewis drift—named by analogy to similar effects in fluid dynamics where waves produce a small forward motion.
2. Why Does a Spinning Gyroscope Cause Drift?
2.1. Not Just a Spin in Place
In a simple world, if you only spin something (apply a rotational force, known as torque), nothing moves linearly. If you’re sitting in a chair and spin a toy wheel on your lap, your body might twist a bit, but you don’t suddenly glide across the room. In a free-floating system with no external influences, the forces you apply remain “internal,” and nothing changes overall.
2.2. Enter the Chain and Friction
However, our system isn’t free-floating—it’s made of three orbs connected by a chain. This chain acts as a rigid link, meaning if one orb tries to twist or move, the other orbs are forced to respond. Here’s where two key elements come in:
Chain Constraints: Because the weights are tied together by a chain that doesn’t stretch, when you try to turn one of them (via the gyroscope), the chain forces the others to adjust. Instead of just rotating in place, the whole system experiences small pushes and pulls.
Friction (or Damping): In real life, there’s always some resistance—whether from the air, the ground, or internal friction. This friction acts like a tiny brake. When the system is jostled, friction prevents it from simply oscillating back and forth perfectly. Instead, each little movement is “imperfect” enough that a small bit of motion isn’t completely undone. Over many cycles, these little bits add up, producing a slow, steady drift.
3. Breaking Down the Effect: The “Lewis Drift” Analogy
3.1. What Is Lewis Drift?
In oceanography, Stokes drift (this is the analogy to the Lewis drift) describes how water particles in waves don’t just move up and down—they follow slightly closed loops that, over time, result in a net motion. Even though each wave cycle seems to bring a particle back to its starting point, the loop isn’t perfectly closed, so there’s a little extra movement in the direction of the wave.
In our mechanical system, the spinning gyroscope produces cycles of small movements. The chain’s constraints and friction ensure that these cycles don’t cancel out perfectly. Instead, they create a tiny imbalance that makes the whole set of orbs slowly drift.
3.2. How the Drift Builds Up
Every time you apply a torque with the gyroscope, Orb 1 (which carries the gyroscope) experiences a reaction. Because it’s connected by a chain to the other two orbs, this reaction force isn’t isolated. The chain transfers part of this force to the other orbs, and they all move a little. With friction acting like a “memory” that prevents complete reversal of the motion, each cycle leaves behind a small net displacement.
Imagine walking on a slick floor—you might take a step, but if the floor is a bit sticky, you won’t slide back exactly when you lift your foot. Over many steps, you end up moving forward. That’s essentially what’s happening here.
4. The Role of the Gyroscopic Reaction Force
4.1. Gyroscopes and Reaction Forces
When a gyroscope spins, it has a large amount of angular momentum (which you can think of as its “spin energy” holding it in a given orientation). If you try to change its orientation—say, by applying a torque—the gyroscope resists this change by “precessing.” Precession is the phenomenon where the spinning object starts to wobble around an axis perpendicular to the applied torque.
In our system, this precession doesn’t occur in isolation. Since the gyroscope is mounted on Orb 1, the reaction force from trying to change the gyroscope’s spin ends up “pushing” on Orb 1. In an unconstrained system, this reaction would only rotate Orb 1. But because Orb 1 is chained to the other orbs, the force is transmitted through the chain.
4.2. Converting Torque to Force
You might ask, “But isn’t torque a twist, not a push?” And you’re right—in an unconstrained system, a pure torque wouldn’t cause the whole object to slide. However, in our system the constraints mean that the twisting motion is partially converted into a linear push. The key here is that the force from the gyroscopic reaction isn’t perfectly “internal” anymore—it ends up having a small external effect on the system’s overall motion.
5. Checking That the Math Makes Sense (Without the Heavy Equations, they're in the link below)
For those curious about the math but not wanting to wade through the equations, here’s an intuitive summary:
Conservation of Momentum: In any closed system, forces that are “internal” (between parts of the system) normally cancel out, leaving no net movement. But here, because friction is present and the forces don’t perfectly cancel, there’s a net push.
Center-of-Mass Equation: When you add up all the forces acting on the whole system (the three orbs), you find that the frictional forces and the reaction from the gyroscope combine into an equation that predicts a slow, steady acceleration of the center of mass.
Backwards Check: By “working backwards”—that is, starting with the observed drift and then calculating what forces must be present—we confirm that the net force coming from the gyroscope’s reaction (after it’s been modified by the chain’s constraints and friction) is exactly what you’d expect to create that drift.
In short, the math tells us:
The reaction force from the gyroscope (which is derived from the torque you apply) is transmitted through the chain.
Friction ensures that not all of this motion cancels out.
Over time, the tiny imbalances add up, and the center of mass drifts steadily.
6. Bringing It All Together
Let’s recap the journey in plain language:
Setup: You have three masses connected by a chain, with one mass sporting a gyroscope.
What Happens When You Spin the Gyroscope: The spinning wheel resists changes to its orientation (thanks to its angular momentum). When you try to force a change, the gyroscope “pushes back” on the mass that holds it.
The Role of the Chain: Because the masses are connected, this push is not isolated to just one mass. The chain transmits part of that force to the other masses.
Friction’s Part: Friction (or damping) stops the masses from simply oscillating back and forth perfectly. Instead, each cycle leaves behind a tiny extra bit of motion.
The Result – Lewis Drift: Over many cycles, these tiny extra motions add up, making the whole system slowly drift in one direction.
Verification: By reversing the analysis (starting from the drift and working back to the forces), we confirm that the numbers and physical laws all add up.
7. Why Should You Care?
This isn’t just a theoretical exercise. The idea that a spinning object can produce a net translation in a constrained system is central to the way some spacecraft and robots work. For instance, satellites use reaction wheels (which are essentially gyroscopes) to adjust their orientation. In more complex systems, similar principles can be used to move or stabilize a craft without using traditional thrusters.
The phenomenon also serves as a great example of how constraints (like chains) and energy dissipation (friction) can convert one kind of motion (rotation) into another (translation). It challenges our everyday intuition about motion and forces, showing that even seemingly “internal” actions can have unexpected external consequences.
8. Final Thoughts
In everyday language, what we’ve shown is this: When you spin a wheel inside a group of connected objects, you can make the whole group slowly slide across the floor—even if you never “push” it directly. This effect, called Lewis Drift, happens because the forces that usually cancel out are instead channeled in a specific direction by the chain, and friction ensures that not everything resets perfectly each time.
Understanding this concept requires a bit of imagination about how forces add up over time and how small imperfections can lead to noticeable movement. It’s a beautiful reminder that in physics, the details of how things are connected—and how energy is lost—can make a big difference in what you see happening.
To see these forces in action, please view the #StarTrekNOW! videos on YouTube:
To learn the math of how to calculate the Lewis Drift:
https://qmichaellewis.blogspot.com/2025/03/chain-together-3-orbs-and-gyro-lewis.html