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SCIENCE · INVESTIGATE AND EXPLAIN

Infer inertial mass while retaining a force-reading fault

A force-versus-acceleration plot can estimate inertial mass only under explicit force and measurement assumptions. Here independent acceleration labels are stipulated exact. The synthetic true mass is 2 kg and force readings follow ma+o, where o is a common additive readout offset. A second selected fault affects only the high-acceleration reading.

Learning outcome: Compare offsets−2,0,2 N at zero fault, then vary fault at one offset. Retain slope, intercept and held-out residual. Propose a changed acceleration that would test a curved force law rather than merely repeat one fitting point.

Starting recap

Draw recipient-specific interactions, resolve signed components and identify the domain of each force/contact model before substituting.

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Try

For offset o=1 N and high-point faultδ=0.2 N, readings are3 and 7.2 N. Fitted mass is 2.1 kg and intercept0.9 N. The held-out5 N reading lies0.1 N below the fitted line.

Open the experiment

Predict

A common additive force offset applied to both fitting readings changes:

Experiment

Compare offsets−2,0,2 N at zero fault, then vary fault at one offset. Retain slope, intercept and held-out residual. Propose a changed acceleration that would test a curved force law rather than merely repeat one fitting point.

Fit inertial mass without confusing a force offset

Worked teaching model · synthetic values · Synthetic true mass 2 kg; readings at independently known accelerations 1 and 3 m/s² are ma+offset, with extra selected fault only at the second point. A held-out 2 m/s² reading has the common offset but no extra fault. No real instrument is calibrated.

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Two-point fit and a held-out force reading

indicated force (N)independently known acceleration (m/s²)037.20

Unlike graph quantities rescale independently; read units and values, not screen angles. 1: fitted affine force model (solid).2: fitting readings (filled markers).3: held-out reading (filled markers). Joined curves show the supplied model, not additional observations.

Equivalent numerical coordinates for Two-point fit and a held-out force reading

fitted affine force model

independently known acceleration (m/s²)indicated force (N)
00.9
37.2

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

fitting readings

independently known acceleration (m/s²)indicated force (N)
13
37.2

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

held-out reading

independently known acceleration (m/s²)indicated force (N)
25

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

Calculated quantities under the declared measurement model
QuantityValueUnit
Force reading at acceleration 13N
Force reading at acceleration 37.2N
Fitted inertial mass2.1kg
Fitted force offset0.9N
Held-out force reading at acceleration 25N
Held-out residual observed minus fitted-0.1N
Mass error bound for independent endpoint ±0.1 N0.1kg

Slope estimates inertial mass; an additive force offset affects the intercept, but a one-point fault affects both.

Subtract force readings to cancel their common offset: fitted m=(F3−F1)/(3−1)=2+fault/2. Intercept becomes offset−fault/2 and the independent midpoint residual is −fault/2. The separate ±0.1 N endpoint-reading bound gives worst-case slope uncertainty ±0.1 kg for exact acceleration labels; it does not cover the selected systematic fault unless explicitly included. A zero residual at one midpoint cannot prove all calibrations or every possible force law.

Predict before inspecting the values. Save contrasting records with assumptions and one alternative explanation. This virtual display does not certify practical measurement technique.

Slope estimates inertial mass; an additive force offset affects the intercept, but a one-point fault affects both.

Subtract force readings to cancel their common offset: fitted m=(F3−F1)/(3−1)=2+fault/2. Intercept becomes offset−fault/2 and the independent midpoint residual is −fault/2. The separate ±0.1 N endpoint-reading bound gives worst-case slope uncertainty ±0.1 kg for exact acceleration labels; it does not cover the selected systematic fault unless explicitly included. A zero residual at one midpoint cannot prove all calibrations or every possible force law.

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Define the recipient and model

A force-versus-acceleration plot can estimate inertial mass only under explicit force and measurement assumptions. Here independent acceleration labels are stipulated exact. The synthetic true mass is 2 kg and force readings follow ma+o, where o is a common additive readout offset. A second selected fault affects only the high-acceleration reading.

Build the algebraic relationship

The fitting accelerations are1 and 3 m/s². Their force readings are2+o and 6+o+δ N. Subtracting cancels the common offset: fitted mass is(4+δ)/2=2+δ/2 kg. The fitted intercept is o−δ/2 N. A common force offset does not change the slope, but a fault on only one point changes both slope and intercept.

Check the changed state

A held-out reading at 2 m/s² has value4+o N without the extra fault. The fitted line predicts4+o+δ/2, so observed-minus-predicted residual is−δ/2 N. This is a genuine unused point in the synthetic fitting exercise. A zero residual at one point still cannot establish every calibration or exclude all possible nonlinear alternatives.

Interpret evidence and limits

Separately, if each fitting force reading has an independent bounded error±0.1 N, their difference has worst-case error±0.2 N. Dividing by the exact acceleration separation2 m/s² gives a mass-error bound±0.1 kg. This deterministic interval is not a confidence level and does not automatically cover the selected systematic fault. Acceleration-scale uncertainty would require additional propagation.

Worked original packet

For offset o=1 N and high-point faultδ=0.2 N, readings are3 and 7.2 N. Fitted mass is 2.1 kg and intercept0.9 N. The held-out5 N reading lies0.1 N below the fitted line.

Bounded investigation

Compare offsets−2,0,2 N at zero fault, then vary fault at one offset. Retain slope, intercept and held-out residual. Propose a changed acceleration that would test a curved force law rather than merely repeat one fitting point.

Changed-case numerical practice

Try the changed case before feedback

Force readings 5 and 11 N occur at independently known accelerations1 and 3 m/s² under an affine force-reading model. Find fitted inertial mass in kilograms.

This practice is public and unsaved. A matching number does not verify understanding. Retain your explanation, assumptions and changed-case evidence in the separate course workspace.

Sources and boundaries

Original prose, data and diagrams checked 30 October 2026 against OpenStax College Physics 2e. This is an algebra-based virtual evidence exercise, not a physical experiment, equipment certification, transport recommendation or independent mastery result. Save assumptions and a competing explanation with the course evidence; supervised practical requirements remain external.

Apply

A common additive force offset applied to both fitting readings changes:

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Why must an uncertainty budget say which errors it includes and which it does not?

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