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SCIENCE · INVESTIGATE AND EXPLAIN

Keep the zero-energy escape limit distinct from finite turning

For radial outward motion in the supplied μ = 1 field, angular momentum is zero and specific energy is v²/2 − 1/r. The potential reference is zero at infinity. Escape speed at starting radius r₀ is sqrt(2/r₀), the speed that makes this energy exactly zero.

Learning outcome: Derive and compare sub-escape, exact-escape and above-escape branches, retaining the infinity reference and the absent surface model.

Starting recap

Integrate mass moments about named axes, derive torque and angular-momentum constraints, and test orbital energy, angular and numerical consistency against independent evidence.

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Try

At r₀ = 2 m and f = 1.5, energy is 0.625 m²/s² and asymptotic speed is sqrt(1.25) ≈ 1.11803 m/s. This differs from the initial speed 1.5 m/s.

Open the experiment

Predict

At exactly the local escape speed, the ideal radial motion has:

Experiment

Derive and compare sub-escape, exact-escape and above-escape branches, retaining the infinity reference and the absent surface model.

Distinguish finite turning radius from escape energy

Worked teaching model · synthetic values · Radial outward test-particle motion with zero angular momentum in mu=1 field. Speed is a selected fraction of sqrt(2mu/r0), so fraction1 is an exact analytic zero-energy boundary. No physical launch, central surface or inward collision model.

Reset keeps your prediction, captures and practice history.

Inverse-square potential reference at infinity

specific potential (m²/s²)radius (m)0120-0.5

Unlike graph quantities rescale independently; read units and values, not screen angles. 1: −1/r (solid). Joined curves show the supplied model, not additional observations.

Equivalent numerical coordinates for Inverse-square potential reference at infinity

−1/r

radius (m)specific potential (m²/s²)
2-0.5
2.125-0.4705882
2.25-0.4444444
2.375-0.4210526
2.5-0.4
2.625-0.3809524
2.75-0.3636364
2.875-0.3478261
3-0.3333333
3.125-0.32
3.25-0.3076923
3.375-0.2962963
3.5-0.2857143
3.625-0.2758621
3.75-0.2666667
3.875-0.2580645
4-0.25
4.125-0.2424242
4.25-0.2352941
4.375-0.2285714
4.5-0.2222222
4.625-0.2162162
4.75-0.2105263
4.875-0.2051282
5-0.2
5.125-0.195122
5.25-0.1904762
5.375-0.1860465
5.5-0.1818182
5.625-0.1777778
5.75-0.173913
5.875-0.1702128
6-0.1666667
6.125-0.1632653
6.25-0.16
6.375-0.1568627
6.5-0.1538462
6.625-0.1509434
6.75-0.1481481
6.875-0.1454545
7-0.1428571
7.125-0.1403509
7.25-0.137931
7.375-0.1355932
7.5-0.1333333
7.625-0.1311475
7.75-0.1290323
7.875-0.1269841
8-0.125
8.125-0.1230769
8.25-0.1212121
8.375-0.119403
8.5-0.1176471
8.625-0.115942
8.75-0.1142857
8.875-0.1126761
9-0.1111111
9.125-0.109589
9.25-0.1081081
9.375-0.1066667
9.5-0.1052632
9.625-0.1038961
9.75-0.1025641
9.875-0.1012658
10-0.1
10.125-0.09876543
10.25-0.09756098
10.375-0.09638554
10.5-0.0952381
10.625-0.09411765
10.75-0.09302326
10.875-0.09195402
11-0.09090909
11.125-0.08988764
11.25-0.08888889
11.375-0.08791209
11.5-0.08695652
11.625-0.08602151
11.75-0.08510638
11.875-0.08421053
12-0.08333333

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
Local escape speed1m/s
Initial outward speed1m/s
Specific total energy0m²/s²
Unbound or marginally unbound1flag
Asymptotic outward speed0m/s

Nonnegative energy has no finite outer turning radius; the zero-energy limit approaches zero speed only at infinity.

With U(infinity)=0, E=v0²/2−mu/r0. The speed fraction control makes the marginal boundary exact, E=0 at fraction1. Below escape, set final speed0 to find rmax=r0/(1−fraction²). Reaching arbitrarily large radius does not occur in finite time. No real launch or surface-impact prediction is made.

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

Nonnegative energy has no finite outer turning radius; the zero-energy limit approaches zero speed only at infinity.

With U(infinity)=0, E=v0²/2−mu/r0. The speed fraction control makes the marginal boundary exact, E=0 at fraction1. Below escape, set final speed0 to find rmax=r0/(1−fraction²). Reaching arbitrarily large radius does not occur in finite time. No real launch or surface-impact prediction is made.

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

Understand

Keep the zero-energy escape limit distinct from finite turning

For radial outward motion in the supplied μ = 1 field, angular momentum is zero and specific energy is v²/2 − 1/r. The potential reference is zero at infinity. Escape speed at starting radius r₀ is sqrt(2/r₀), the speed that makes this energy exactly zero.

The control selects a fraction f of that local escape speed. Energy becomes (f² − 1)/r₀. For f below 1, set speed to zero at the outer turning radius to obtain rmax = r₀/(1 − f²). This finite turning point is not the starting radius and is not computed by using constant near-surface g over a large distance.

At r₀ = 2 m and f = 0.5, energy is −0.375 m²/s² and outer turning radius is 8/3 m. At f = 1, energy is exactly zero, there is no finite outer turning point and speed tends to zero only as radius tends to infinity. Reaching infinity still takes infinite time.

For f above 1, the asymptotic speed is sqrt(2E), positive. All branches here are ideal radial test-particle statements; the model excludes central-body size, atmosphere, inward impact and physical launch procedures. Setting an arbitrarily tiny computed energy to zero would alter the escape classification, so the exact control-defined f = 1 boundary is treated analytically.

Changed-case check

Predict before reading the comparison. At r₀ = 2 m and f = 1.5, energy is 0.625 m²/s² and asymptotic speed is sqrt(1.25) ≈ 1.11803 m/s. This differs from the initial speed 1.5 m/s.

Retained investigation

Derive and compare sub-escape, exact-escape and above-escape branches, retaining the infinity reference and the absent surface model. Why does an energy equation alone not supply the elapsed travel time?

Source and boundary

Primary conceptual reference checked 30 October 2026: OpenStax University Physics Volume 1. All models, packets and teaching prose are original. These are bounded mathematical investigations, not measured apparatus, physical procedures, practical certification or institutional credit.

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At exactly the local escape speed, the ideal radial motion has:

Public practice checks a specific claim. It does not establish independent mastery.

Why does an energy equation alone not supply the elapsed travel time?

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