NO MOTOR?

What will you explore?

Li and colleagues, 2016

A surface can turn heat-driven vapor flow into directed motion.

How does it work?

Watch a 90-second cinematic explanation, or explore a story that pauses so you can change its central mechanism. Inspect the source evidence, compare outcomes and resume the narration. This free Lesson Worlds adaptation needs no account or download; younger learners may want help from a parent or teacher.

Inside the cinematic story

1. NO MOTOR?

   NO MOTOR?

2. The hidden vapor cushion

   The hidden vapor cushion

3. One surface, a preferred direction

   One surface, a preferred direction

4. Take away the ratchet

   Take away the ratchet

   Take control: What gives the vapor a preferred direction? Asymmetric ratchet · Flat reference

5. A smaller droplet moves faster

   A smaller droplet moves faster

   Take control: Which selected model case moves faster? Larger model droplet · Smaller model droplet

6. Heat powers the motion

   Heat powers the motion

Discuss the evidence

Before starting, explain what you think this claim means: A surface can turn heat-driven vapor flow into directed motion. After exploring, choose one stage above and describe what its model helps you see. Separate what you observed in the adaptation from what the original researchers measured.

Read the original publication for its methods, evidence and limitations. Ask which part of the explanation the interactive model leaves out, and what additional evidence you would need to test the claim yourself.

Original qualitative 3D teaching reconstruction of Li, Kang, Francois and Hu (Soft Matter 2016; accepted preprint 2015), Sections 3.2 and 4, Figures 4–6. Their thermal multiphase lattice Boltzmann calculation is two-dimensional, with liquid-to-vapor density ratio about 17, compared with about 1000 for real water. This scene is not their solver, measured footage or quantitative validation. Droplet trajectories, enlarged vapor gap, colored tracer paths, deformation and camera movement are prescribed for explanation; no calibrated speed, temperature or time is implied. The smaller-droplet comparison is confined to the selected near-capillary-length model cases, not a universal size law. A flat reference illustrates loss of directional asymmetry, not a newly computed control experiment. The brass material and laboratory set are artistic choices. Heat supplies energy; no motor does not mean no energy.

Original research

Lattice Boltzmann modeling of self-propelled Leidenfrost droplets on ratchet surfaces

Qing Li, Q. J. Kang, M. M. Francois and A. J. Hu · Soft Matter 12, 302–312 (2016); accepted preprint October 2015 · 2016

Educational adaptation by Lesson Worlds. Not affiliated with the authors, Los Alamos National Laboratory or the Royal Society of Chemistry. The original publication may have its own access terms.