Start Here
What AffineDrift Is
AffineDrift is a free, open notebook about how a golf swing moves and why. It uses physics models to split each moment of the swing into what the body and club would do on their own and what the golfer adds. Each page says how strong its evidence is, so you can judge each claim for yourself.
The Big Idea in One Picture
Picture a swing as a point moving across a map of every possible state. At each point, two arrows add up. One arrow is the drift: where gravity and momentum would carry the motion with no effort at all. The other is the push: the change the golfer’s muscles add. The picture below draws both arrows from a simple pendulum model.
src/tangent_models/examples.py; not a golfer measurement.Long description
The horizontal axis is the pendulum angle from straight down, in radians; the vertical axis is its angular velocity, in radians per second. Faint arrows show the drift: the direction the model's state moves at each point with no torque. Both runs start at rest at an angle of -2.2 rad. The dashed curve is the zero-torque run, which follows the drift alone. The solid curve is the run under a constant 5 N m pivot torque, which swings faster and further. At the marked state, angle -1.94 rad and angular velocity 2.68 rad/s, three arrows show the change over 0.35 s: the drift arrow (2.68, 9.16) per second, the push arrow (0, 5.00) per second, which only changes angular velocity because torque acts on acceleration, and their sum, the state velocity the run actually has.
The point of the split is not that one arrow matters more. It is that you can only ask “what did the golfer add?” once you know what would have happened anyway. The Big Idea in Five Minutes explains it with everyday examples, and the Overview explains the scope of the site in more detail.
Choose Your Path
Choose what you want to do first. Each path includes a short start and a route to deeper work.
Explore golf mechanics in plain language, starting with a five-minute introduction.
Build a foundation in mechanics and control, then follow the derivations.
Try simulations and inspect the assumptions behind their results.
Looking to review, integrate, or contribute? Specialist Reading Paths has all eight reader plans, with 5-minute, 30-minute, and 3-hour options.
How to Read the Evidence Labels
Pages and claims carry a label that says how far they have been checked. Read the label before you trust a claim.
- Available: The text, code, or derivation is complete, readable, and open for inspection. Does not imply independent peer review, clinical consensus, or empirical human validation.
- Validated: Specific claims name verifiable empirical evidence, calibration datasets, and exact error bounds. Neighboring claims, untested swing regimes, or full-body extensions do not inherit validation.
- Experimental: Exploratory modeling or software available for discussion and sensitivity testing. Does not guarantee numerical convergence, stable APIs, or verified real-world predictive fidelity.
- Planned: A formal specification or tracking issue exists, but the deliverable is not yet completed. Does not imply active implementation in the current release cycle or guaranteed delivery dates.
- Deprecated: Material preserved strictly for historical context, backwards compatibility, or audit history. Not recommended for current modeling, active research, or pedagogical study.
- Opinion: Editorial synthesis, philosophical positioning, or speculative research agendas. Does not represent mathematical proof, empirical data, or institutional consensus.
A separate evidence ladder says how strong the support is, from pure math up to tests on real people. The full definitions are in How to Read This Site.
What This Site Is Not
- It is not coaching advice. The models explain motion. They do not tell you how to swing.
- It is not peer reviewed by default. A page being online means you can read and check it. It does not mean experts have signed off on it.
- It is not a validated model of a human. Most results come from simple models of links and joints. They are tools for thinking, not a measured picture of any real golfer.
Citation
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