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Yank (physics)

The first time derivative of force, distinguishing how fast a force changes from the force level itself across measured or modeled force trajectories.

Version
v1 · 2026-10-31 · History
Domain-specific #
14599
Domain group
Natural Sciences
Origin domain
Physics
Subdomain
Force Time Analysis → Physics
Aliases
Force yank

Core Idea

Yank is the first time derivative of force: for a differentiable trajectory \(\mathbf F(t)\), \(\mathbf Y(t)=d\mathbf F/dt\). It describes the rate and direction of force change rather than the force level. The derivative of a selected scalar component has a sign relative to its axis.[1]

How would you explain it like I'm…

How Fast a Push Changes

When you push a swing, your push can get stronger or weaker. Yank tells you how fast your push is changing, not how hard you're pushing. You can still be pushing hard while the yank says your push is quickly getting weaker.

How Fast a Force Changes

A force is a push or a pull. Yank (physics) tells you how fast a force is changing at a moment, and in which direction, rather than how strong the force is. For example, when you jump, the floor pushes up on you, and yank shows when that push is rising quickly or dropping quickly, even while the floor is still pushing. The name was suggested by scientists who study body movement, and it isn't yet a standard word everywhere in physics. Because real measurements are a bit bumpy, scientists have to say how they calculated it.

Time Derivative of Force

Yank (physics) is the rate of change of force over time, Y = dF/dt. It describes how fast and in what direction the force vector is changing at an instant, not how large the force is. For a single measured direction, like the vertical force from the ground during a jump, yank can be positive or negative, marking a fast rise or fall while the force itself is still nonzero. The name was proposed in a 2019 biomechanics paper, which noted it wasn't yet standard across physics; later studies used it for jump force data and for grip force compared with brain activity. Since real force data are sampled and noisy, a computed yank is an estimate, and a rate measured between two points over an interval is an average, not the instantaneous value.

 

Yank (physics) is the first time derivative of force: for a differentiable force trajectory F(t), Y(t) = dF/dt. It reports the instantaneous rate and direction of change of the force vector, not the force's magnitude. For a chosen scalar component, such as vertical ground-reaction force, the component derivative carries a sign relative to that direction, and a positive or negative peak can mark a rapid rise or fall while the force remains nonzero. The term was proposed for the force derivative in a 2019 biomechanics Commentary, which noted that it was not then standard throughout physics. Later work applies the same metric to different force records: Sahrom and colleagues derived vertical yank from force-platform data to study countermovement-jump events, and Jiang and colleagues estimated grasp-force derivatives and compared them with cortical activity. These are uses of one force-derived metric, not evidence of a universal neural or movement mechanism. An exact derivative belongs to a differentiable model; measured records are sampled and noisy, so a yank trace is an estimate whose sampling, filtering and component choice must be stated, and a two-point rate of force development over an interval is an average rate, not automatically the instantaneous derivative.

Structural Signature

  • Force trajectory: force, or an explicitly selected component, varies with time.
  • First time derivative: yank is the local change rate where the derivative exists.
  • Readout: a component derivative does not recover unmeasured vector components.
  • Empirical estimate: sampled force requires a differentiation method and often filtering; noise and resolution affect the result.[1][2][3]

What It Is Not

Force is the quantity differentiated; impulse integrates it. A finite-window rate of force development is an interval average rather than automatically a pointwise derivative. Jerk times mass gives yank only under an appropriate constant-mass force law. A measured association with a biological signal does not establish a causal mechanism.[1][3]

Examples

Countermovement jump. Researchers estimated the derivative of vertical ground-reaction force, then rectified and smoothed it for selected event tests against motion and muscle measurements. Rectification removes the original sign; the authors did not claim every jump event can be identified from yank alone.[2]

Hand grasp. Researchers estimated the derivative of scalar grip force in four patients and compared it with cortical-band activity. The reported onset association does not establish a general causal law, and the analogous offset advantage was not statistically significant.[3]

Reasoning and Boundary

For a differentiable model, differentiate force with respect to time. For sampled data, report the component, sampling interval, differentiation and filtering, then validate the particular interpretation. A high sustained force can have near-zero yank; yank alone cannot recover the force level without an initial condition.[1][2][3]

Neighborhood in Abstraction Space

Yank (physics) sits in a sparse region of the domain-specific corpus (99th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (2835 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-31

References

[1] David C. Lin, Craig P. McGowan, Kyle P. Blum and Lena H. Ting, “Yank: the time derivative of force is an important biomechanical variable in sensorimotor systems,” Journal of Experimental Biology 222 (2019), jeb180414, DOI 10.1242/jeb.180414, https://bpb-us-w1.wpmucdn.com/sites.usc.edu/dist/1/927/files/2023/02/JEB-2019_Yank.pdf (published original Commentary, full PDF inspected; pp. 1–4 define the proposed name, vector derivative, interval-average RFD, conditional jerk relation and noise boundary). registry ↩a ↩b ↩c ↩d

[2] Sofyan B. Sahrom, Jodie C. Wilkie, Kazunori Nosaka and Anthony J. Blazevich, “The use of yank-time signal as an alternative to identify kinematic events and define phases in human countermovement jumping,” Royal Society Open Science 7 (2020), 192093, DOI 10.1098/rsos.192093, https://upload.wikimedia.org/wikipedia/commons/b/b0/The_use_of_yank-time_signal_as_an_alternative_to_identify_kinematic_events_and_define_phases_in_human_countermovement_jumping.pdf (original open-access article, full PDF inspected; §§2.4, 3.2 and 4.1–4.3 describe force, processing and event limits). registry ↩a ↩b ↩c

[3] Tianxiao Jiang et al., “Power Modulations of ECoG Alpha/Beta and Gamma Bands Correlate With Time-Derivative of Force During Hand Grasp,” Frontiers in Neuroscience 14 (2020), 100, DOI 10.3389/fnins.2020.00100, https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2020.00100/full (original research, full publisher HTML inspected; §§2.2, 2.7, 3.3 and 5 describe the four-patient task, yank estimate and onset/offset correlation limits). registry ↩a ↩b ↩c ↩d