01 · The Forces
Glide is the result, not a force of its own.
Flight has four forces: lift, weight, thrust and drag. Gravity Scheduling uses all of them. Glide is what you get when they act on the work together.
Glide=Thrust−Dragacross the dependency graph
When glide slips, the color tells you how bad it is. Thrust and drag tell you why. The right Lift depends on the cause: adding people does nothing for a team buried in scope growth.
Every item that is Drifting or worse should name its primary drag source.
The five forces
What each force means.
- GlideWhat will happen · reality
Where work will land based on real team capacity and flow. Computed by forward scheduling from today: every task is placed on the earliest day its dependencies and team capacity allow.
Needs a live source of truth. If the work isn't on the board, glide can't be measured, and you're left taking verbal commitments.
- GravityWhat must happen · intent
Where work is pulled by deadlines and commitments. Computed by backward scheduling from fixed milestones: each earlier milestone gets the latest date it can have without endangering anything downstream.
Written down and stable, so the paper is the bad guy, not the person. Work with no gravity is unanchored, which is not the same as on track.
- LiftWhat we do about it · decision
The corrective action taken when glide and gravity diverge, sized to the gap: light, moderate, diagnostic or structural.
- ThrustWhat moves work forward
Team velocity, people assigned, concurrency limits, automation and skills.
- DragWhat slows work down
Scope growth, dependency waits, rework, interruptions, meetings and context switching.
Where each force lives
Gravity at the top, glide at the bottom.
Initiatives and epics carry gravity: fixed milestone dates that leadership reports on. Stories and tasks carry glide: they flex every day as stand-ups add, split and move work.
The two meet at the boundary between epic and story. That is where glide is compared against gravity.
Drag sources
Name the drag, then choose the Lift.
Each drag source leaves a different signal in the data and calls for a different correction.
| Drag source | Signal | Lift that fits |
|---|---|---|
| Scope growth | Task count under the epic rising week over week | De-scope, split the epic, re-confirm gravity |
| Dependency wait | Work is ready but blocked on another team | Re-sequence, escalate the upstream gravity |
| Rework | Tasks reopened or failing test | Fix quality at the source; slow down to speed up |
| Interruption | Unplanned work entering the queue | Protect capacity; route interrupts to a rotation |
| Coordination load | Meeting hours rising, focus time falling | Reduce meetings with Uplink & Downlink |
| Thrust loss | Velocity falling with no rise in drag (absence, attrition) | Add or rebalance capacity |