Can Spider-Man Stop a Train?

Scientific concepts / nature phenomena presented

Kinematics & energy (work–energy / kinetic energy)

• “Stopping” the train is framed as doing physical work to remove the train’s kinetic energy.
• The train comes to zero final velocity, so the required absorbed energy is modeled as its initial kinetic energy.
• Conceptual relationship used: work done by the webbing = change in kinetic energy.

Material science: stress–strain and toughness

The discussion introduces a stress vs. strain curve:

• Stress = force per unit area.
• Strain = deformation (stretching/compressing).
• Yield strength: where deformation increases without much additional force.
• Rupture: where the material breaks.

Toughness

• Defined as the area under the stress–strain curve.
• Interpreted as the material’s energy absorption capacity (with units of energy per volume).
• Key claim: spider silk’s toughness—its ability to absorb energy while deforming/stretching—is central to whether it could stop a train.

Comparing material toughness values

• Steel toughness is referenced as approximately 6 million J/m³ (for comparison).
• A “real spider silk” comparison is presented as far tougher:
  • Dragline silk (golden orb-weaver) is described with toughness around 150 in the video’s units (presented as ~25× tougher than the steel comparison).
• A more extreme hypothetical uses Darwin’s bark spider silk:
  • Described as ~10× tougher than Kevlar, used to improve feasibility.

Back-of-the-envelope scaling calculation

Method steps (as outlined in the subtitles):

1. Estimate train mass

   • Each car mass estimated at 38,000 kg.
   • Number of cars assumed: 6.

2. Estimate train speed

   • 80 mph ≈ 35 m/s.

3. Assume passenger load

   • Cars near capacity.
   • Average passenger mass: 62 kg.

4. Compute train kinetic energy

   • Reported as approximately ~187 million joules.

5. Use toughness to estimate required energy absorption per unit volume

   • Determine how much energy the silk must absorb, based on its toughness.

6. Estimate available web volume

   • From a movie-style observation:
     • “8 web lines per hand” idea, with 8 contact points, leading to 128 total web lines in the described count.
   • Each line is modeled as roughly:
     • 3.5 mm radius (pencil-like thickness),
     • ~15 m long.
   • Use these to compute total web volume.

7. Apply an inequality criterion

   • Check whether the web’s “energy capacity” is sufficient.
   • If the computed value is ≤ 1, the web is deemed enough (or more than enough) to absorb the train’s kinetic energy.

Results presented

• With “orb-weaver” toughness:
  • The model yields a result around 1/3 to 13× too small, suggesting it’s not enough without stronger/thicker assumptions (video language).
• With “Darwin’s bark spider silk”:
  • The model gives about 4, reported as enough (depending on interpretation of variables).
• Using the same toughness, the model also estimates:
  • Approximately 70 strands of webbing needed (about 35 per hand) to meet the energy requirement with the tougher bio-silk assumption.
• A further adjustment claims feasibility improves if strands are thicker (twice as wide):
  • This can make the model reach a feasible value with a more “movie-like” strand count,
  • but it implies an unrealistic bulk/quantity of webbing (described as holding onto scaffolding).

Model sensitivity / uncertainty (assumptions drive conclusions)

The narrator emphasizes that conclusions shift dramatically based on assumptions about:

• Train acceleration, modeled as coasting rather than accelerating.
• Whether the silk can stretch extensibly:
  • Subtitles state that extensibility beyond what’s seen may be unrealistic.
  • Even limited stretch is claimed to still produce significant deceleration.
• Web dimensions, including:
  • strand thickness and length
• How many strands are actually used/attached.

Researchers or sources featured (listed at end, per subtitles)

• Christopher (host/speaker)
• Tobey (mentioned in the subtitles as part of “Do the math and you get…”; not clearly identified as a researcher)
• Mentions of Doc Ock and Peter Parker / Spider-Man / Spider-Man 2 (fictional characters; not researchers)

No specific real academic researchers were explicitly named in the subtitles provided.