Domain: Engineering — Mechanical Engineering
Target concept: Thread

Video generation prompt: Fix two screw rods of the same diameter on the test bench, machined into rectangular threads and trapezoidal threads respectively, and thread the same nut onto each screw rod. Attach a spring dynamometer to each nut, and pull both nuts along their rods' axes at the same time, gradually increasing the applied force, while observing the reading on each dynamometer as the nuts begin to move.

Evaluation guide:
(i) Target concept: Mechanical advantage and frictional resistance differences between rectangular and trapezoidal screw threads under axial loading.
Minimum mechanism: Rectangular threads engage with a near-zero radial thrust component, keeping the normal force (and thus friction) low; trapezoidal threads generate a substantial radial component from their angled flanks, increasing clamping force and sliding resistance. As the pulling force on both nuts is ramped up at the same rate, the rectangular-thread nut breaks loose and starts sliding (and keeps advancing farther) at a lower dynamometer reading than the trapezoidal-thread nut needs before it starts to move.
(ii)Storyline: Frame 0–2: Static wide shot showing both rods mounted, threads clearly differentiated, nuts fully seated. Frame 3–5: Dynamometers attach simultaneously to each nut; cables align precisely with rod axes. Frame 6–8: Pulling force is applied to both dynamometers at the same time and increased gradually; the rectangular-thread nut breaks loose and begins sliding first, at a lower force reading, and by frame 8 has advanced visibly farther than the trapezoidal-thread nut, which needs a higher force before it starts to move. Frame 9: Final state shows this differential displacement and the corresponding dynamometer readings (smaller for rectangular, larger for trapezoidal); viewpoint remains fixed, orthogonal, and unobstructed throughout; no rotation or wobble of nuts or rods occurs.

Manual:
Experimental Procedure
1. Mount two identical-diameter screw rods side-by-side on test bench: one with rectangular threads, one with trapezoidal threads.
2. Thread the same nut onto each rod.
3. Attach a spring dynamometer to each nut. Pull both nuts along their rod axes at the same time, gradually increasing the applied force, and read each dynamometer as its nut begins to slide.
Observation of Experimental Phenomena
The rectangular-thread nut breaks loose and starts sliding at a lower dynamometer reading, and it advances farther than the trapezoidal-thread nut by the end of the pull; the trapezoidal-thread nut requires a higher dynamometer reading before it begins to move.
Summary of Experimental Principles
Rectangular threads have higher mechanical efficiency and lower friction than trapezoidal threads because their flanks produce a much smaller radial (normal) force component. As the pulling force on both nuts is increased at the same rate, this lets the rectangular-thread nut break loose and keep advancing at a lower force reading than the trapezoidal-thread nut, which needs a higher force to overcome its greater thread friction.

Prompt Grounding rubric:
level_1: No test bench is shown; the two screw rods, one with a rectangular thread and one with a trapezoidal thread, do not both appear in the shot; no nut is shown on either rod; no spring dynamometer appears anywhere; no pulling action is depicted at all.
level_2: The test bench and two same-diameter screw rods are shown side by side, but the thread type of at least one rod cannot be told apart from the other, so rectangular versus trapezoidal is not distinguishable; only one nut is visible and it is not clearly threaded onto either rod; a spring dynamometer appears somewhere in the shot but is not touching any nut.
level_3: The test bench holds two same-diameter screw rods side by side: one clearly shows a rectangular thread profile (flat crest, square-cornered flanks roughly perpendicular to the rod axis) and the other clearly shows a trapezoidal thread profile (slanted flanks, a crest narrower than the root, flank angle of roughly 30 degrees); a matching nut is threaded onto each rod; a spring dynamometer is visibly attached to one nut and pulling it along that rod's axis, while the other nut is also being pulled along its own axis at the same time, even though no dynamometer is yet shown attached to it.
level_4: Everything required for score 3 holds, AND a separate spring dynamometer is visibly attached to each of the two nuts, one dynamometer per nut, each aligned with its own rod's axis; both pulls are strictly along the rod axis, not at an angle; both rods stay fixed and unmoving throughout the pull; nothing blocks the view of either thread profile or either nut's position.
level_5: Everything required for score 4 holds, AND the two dynamometers match each other in construction, size, and orientation; before the pull begins, each nut sits at the same relative position on its own rod, for example both centered or both the same distance from the rod's fixed end; the full thread profile of each rod stays visible along its engaged length throughout; no frame shows either nut misaligned, slipping off the thread, or only partially threaded on; the camera holds one fixed, level view of the bench for the entire clip.

Scientific and Causal Correctness rubric:
level_1: There is no visible difference in how the two nuts move; both nuts move by the same amount or neither one moves; the rectangular and trapezoidal thread profiles are shown swapped or mixed up; a nut slips off its rod during the pull; the two dynamometers appear to show matching readings despite the two threads having different geometry.
level_2: The two thread profiles look correctly distinct, but nut motion is missing or unclear, for example both nuts stay still or both move by the same amount; there is no visible sign that one nut resists the pull more than the other; a dynamometer is shown but its reading never appears to change; the link between thread shape and how much the nut resists sliding is not shown at all.
level_3: The nut on the rectangular-thread rod moves farther, or starts moving sooner, than the nut on the trapezoidal-thread rod once the pull is underway; the dynamometer attached to the rectangular-thread nut shows a smaller reading than the one attached to the trapezoidal-thread nut; both nuts move strictly along their own rod's axis, without wobbling or spinning; neither nut loses thread engagement during the pull.
level_4: Everything required for score 3 holds, AND the contrast is unmistakable: the rectangular-thread nut keeps advancing steadily while the trapezoidal-thread nut advances much more slowly or barely moves at all; the two dynamometer readings are clearly and consistently different, with visibly less needle travel on the rectangular-thread side and more on the trapezoidal-thread side; neither nut's motion reverses, stalls, or jerks in a way that breaks from a steady pull; neither thread shows stripping or jamming.
level_5: Everything required for score 4 holds, AND the size of the gap matches what the underlying friction difference predicts: the rectangular-thread nut ends up noticeably farther along its rod than the trapezoidal-thread nut over the same stretch of time; the trapezoidal-thread dynamometer's reading stays clearly and consistently higher throughout; no frame shows either nut losing contact with its thread, spinning without advancing, or drifting off-axis in a way that would distort the force reading.

Spatiotemporal Consistency rubric:
level_1: A screw rod appears to teleport between frames; a nut appears or disappears with no visible sliding motion connecting the two states; a dynamometer snaps into position without ever being attached on screen; the lighting or shadows on the rods change abruptly with no visible cause; a rod appears to bend or fracture partway through; the camera view jumps to a different framing with no natural transition.
level_2: The rods stay in roughly the same place but visibly vibrate or judder; a nut's sliding speed is inconsistent, suddenly speeding up or stopping; a dynamometer's cable visibly kinks, or appears to detach and reattach between frames; the thread region is briefly blocked from view in more than one frame; the lighting flickers or the shadows on the rods shift inconsistently.
level_3: Both rods stay rigid and stay in the exact same place throughout; each nut slides continuously along its own rod's axis without unexplained stops or restarts; each dynamometer's cable stays taut and straight for the whole pull; nothing unexpectedly enters or exits the frame; the lighting on the rods and their cast shadows keep the same brightness and direction from start to finish; the camera holds one fixed, level view with no panning, tilting, or zooming.
level_4: Everything required for score 3 holds, AND each nut's forward motion looks smooth, without stutter or a sudden jump in speed; each dynamometer cable's tension looks visually constant, without a visible slack-to-taut snap; the region where the nuts meet the threads stays fully visible and steadily framed; there is no sideways drift in the view that would suggest the camera itself moved.
level_5: Everything required for score 4 holds, AND the motion blur on the moving nuts and cables looks consistent with their own speed and direction rather than mismatched or patchy; the rod ends and bench edges hold rock-steady, without any visible flicker or vibration; the thread crests on both rods stay crisp, without visible flicker along their edges; the position of each nut and the angle of its dynamometer cable stay in visible sync with each other in every frame.