Shop class · Intro physics

Soft Matter Lab

WaveCrestThe crest travels. The float stays on its mast.
ClothTensionOne pull. Neighbors share the tension.
FlowInkThe ink itself is carried downstream.
SkinBeadThe skin pulls a drop into a bead, or lets it wet out.
SoftBodyThe shape changes. The body stays one piece.
MediumStuffThe stuff a wave moves through.
FloatPushSame size. The fluid pushes up.
ThickSlowSame drop. A thicker liquid gives more slowly.
ClimbNarrowA narrower opening climbs higher.
DyeSpreadDye spreads through still water. No current carries it.
RatePunchSlow push sinks. A hard hit holds.
DepthPressDeeper water pushes harder.

A lab for shop class and intro physics. Waves, cloth, flow, soft bodies, and how liquids push, climb, spread, thicken, and press harder with depth. Watch what moves — and what stays.

HS / intro college Tension is shared Energy moves · matter may stay A drop's skin · bead or wet-out Shape changes · body stays one piece Pulse travels · beads stay Same size · float or sink Same drop · thicker is slower Narrower path · climbs higher Still water · dye spreads Slow push flows · a hard hit holds Deeper water · harder push

Enter the lab

Specimen 01 — Wave basin

The crest travels. The water stays.

A wave moves energy through a material. The crest runs from the paddle to the far wall, and the water under it only rises and falls.

Note — energy crosses the tank. The colored floats do not.

A traveling wave carries energy from the orange paddle to the far wall.

The water under a crest mostly moves up and down.

Each float is a bit of material on a fixed mast. A float near the paddle crests before a float downstream.

A stone makes a ring. The ring spreads. The floats still stay on their masts.

In the world

A luthier shapes a guitar or piano string so a wave can run along it while the string stays on the instrument. A structural engineer uses the same idea on a bridge: wind and traffic send a vibration along the deck, and the deck stays where it was built. Both jobs need a clear split between what travels and what stays, so a string rings clean and a bridge does not shake itself apart.

Common mistakes

The water does not travel with the crest. It stays in place and bobs.
A float does not slide along the tank. It stays on its mast.
A ring that spreads is not water flowing outward. The ring moves. The floats stay.

Try this

Watch the gold float, then the blue one. Which crests first? Click the water to drop a stone. The ring moves. The float does not slide along its mast.

Amplitude 0.16 Tempo 0.90 Damping 0.22

Crest travels · float stays

Specimen 02 — Cloth

The sheet shares the tension.

Tension is a pull shared across a cloth. Tug one stitch and the neighbors take the load, so the whole sheet curves together.

Note — pull one stitch. The threads around it take the load.

The cloth is a grid of points tied to their neighbors.

A force at one point becomes a curve across the sheet. That shared pull is tension.

The colored stitches are material. They stay in the weave. They move because the weave pulls them.

Wind is a push spread over the whole cloth. The sheet bows together.

In the world

A cloth-simulation artist in film and games sets this shared pull so a cape, a flag, or a dress moves as one sheet. A sailmaker cuts panels so the wind's push spreads across the whole sail. A parachute rigger checks the same thing on a canopy: the cloth has to open together and carry the load as one piece.

Common mistakes

The stitch you pull is not the only one that moves. Neighbors share the tension.
Colored stitches do not slip out of the cloth. They stay in the weave.
Wind does not pick off one thread at a time. The whole sheet bows together.

Try this

Drag the lower cloth. Watch the tug climb toward the rod. Then raise wind, or hit Gust. The colored stitches move as one piece, not one thread at a time.

Wind 0.62 Stiffness 0.78 Damping 0.97

Neighbors share the pull

Specimen 03 — Flow

Here the material moves.

Flow carries the material itself. The ink travels with the current, from one side of the tank to the other.

Note — unlike the floats, each drop travels with the current.

In the wave tank, the floats stayed on their masts.

Here the ink is the material, and the current takes it downstream.

The clay post splits the stream. Lanes go around and meet again.

Slow the speed to zero and the ink stops. A wave crest would not.

In the world

A meteorologist follows air that really travels, the way this ink travels with the current. Clouds, smoke, and rain ride that moving air around hills and through a city. A wind engineer uses the same idea in a tunnel, watching the air itself move past a car or a building.

Common mistakes

Set the speed to zero and the ink stops. A wave crest would not.
The clay post does not end the stream. The ink goes around it and meets again.
Flow is not a wave. A wave moves energy while the material stays. Flow carries the material.

Try this

Follow one large drop from the left, around the post, and off the right. Add swirl. Then set speed to zero and scroll back to the basin. What moved there? What moves here?

Speed 0.72 Swirl 0.22

Ink is carried

Specimen 04 — Centerpiece

Same question. Two soft bodies.

Soft matter changes shape and stays one piece. A crest can travel while the floats stay put, and a cloth can bend while its threads keep hold of one another.

Note — left, the crest moves. Right, the load spreads.

Left: a crest runs the basin. The floats bob in place.

Right: wind loads the cloth. Neighbors share it.

Neither body is rigid. Both keep their material connected.

Soft matter is this: the shape changes, and the piece stays one piece.

In the world

A piano technician hears a wave run down a string while the string stays in the piano. A sailmaker watches wind load a sail while neighboring cloth shares the pull. In both jobs the body is soft: the shape changes, and the piece stays one piece.

Common mistakes

On the left, the floats do not travel with the crest. They bob in place.
On the right, the cloth is not a stiff board. It bends, and neighbors share the load.
Soft does not mean the body comes apart. The shape changes, and the piece stays one piece.

Try this

Watch for ten seconds without touching. Name what travels on the left, and what stretches on the right. Then orbit either view.

Drivers ON

Wave · material stays

Cloth · tension shares

Specimen 05 — Surface tension

The skin pulls the drop.

Surface tension is the inward pull in a liquid's skin. That pull holds a drop as a round bead, or lets the same liquid spread and wet the plate.

Note — surface tension is the pull in a liquid's skin. That pull makes a bead, or lets the drop wet out.

A liquid has a skin. The skin pulls inward.

On a plate that sheds the liquid, the drop stays a tall bead. The foot stays small.

On a plate the liquid likes, the same drop spreads and wets out. It gets short and wide. The amount of liquid does not change.

The colored stitches sit on the skin. They ride the skin. They do not sink inside.

In the world

An inkjet technician counts on a drop's skin to hold each drop as a bead in the air, then to let that ink wet the page. A coatings technician uses the same pull so paint lies flat on metal instead of beading into bare spots. You can see it outside too: rain stays a bead on a waxy leaf and wets out on clean glass.

Common mistakes

Spreading flat does not use up liquid. The same drop gets short and wide.
The colored stitches are not inside the drop. They sit on the skin.
Bead and wet-out are not two different amounts. The skin and the plate set the shape.

Try this

Start on Bead. Poke the drop and let go. The skin pulls it round again. Switch to Wet out and watch that same liquid spread flat. Then raise Skin and poke once more — a stronger skin snaps back faster.

Wetting 0.18 Skin 0.86

Skin pulls · bead or wet-out

Specimen 06 — Soft body

The shape changes. The body stays one piece.

A soft body changes shape and stays one piece. A poke dents the jelly, neighbors take part of the dent, and the amount of jelly stays about the same.

Note — a push dents the jelly. The dent spreads. The jelly does not come apart.

This block is one soft body. Each bit is tied to its neighbors.

Push one spot. The neighbors take some of the dent. The sides swell, because that jelly did not vanish. The amount of jelly stays about the same.

Let go. Stiffness pulls the block back toward its shape. Damping quiets the wobble. Low stiffness and high damping let the dent sit longer.

The colored bits are material in the jelly. They stay in the body. A wave float stays on its mast. Ink is carried away. Here the material deforms with the body and remains part of it.

In the world

A character FX artist builds a soft body so flesh, fat, or a jelly creature can change shape in a shot and still stay one connected piece. A food scientist sets the stiffness of a gummy or a gelatin dessert so a bite dents it without tearing it, while the amount of candy stays the same. A prosthetist uses a silicone liner that changes shape against the limb, keeps its volume, and stays one piece so the socket still fits.

Common mistakes

The dent does not stay only where you poke. Neighbors take some of it.
The sides do not swell because jelly appeared. That jelly did not vanish, so the amount stays about the same.
Letting go does not leave the body in pieces. Stiffness pulls the block back into one piece.

Try this

Poke the top and hold. Watch a colored bit move, and watch the sides swell. Let go. Then lower stiffness, raise damping, and poke again so the dent sits. Hit Drop. The block squashes on the plate and climbs back into one piece. Gravity is its weight.

Stiffness 0.62 Damping 0.40 Gravity 1.00

Shape changes · one piece

Specimen 07 — Particle medium

The pulse travels. The beads stay.

A medium is the stuff a wave moves through. The pulse walks across the beads, and each bead stays over its home mark.

Note — these beads are the medium. The medium is the stuff a wave moves through.

A wave needs stuff to travel through. That stuff is the medium.

Each bead is one particle of the medium. Neighbors pull on neighbors.

The orange bar shoves the beads on the left. Those beads pull the next beads. The pulse walks across the tray.

A colored bead rises and falls over its home mark. It does not cross the tray.

In the flow tank, the ink is carried away. Here the beads stay. Only the disturbance travels.

In the world

A geotechnical engineer follows an earthquake wave through soil. The shaking travels, and each grain of soil mostly stays in place, so the foundation can be built for that motion. A civil engineer uses the same idea in a grain silo: the kernels sit in the bin while the shaking travels through the pile, and the walls have to hold. An avalanche forecaster watches a crack run across a snow slab before the snow itself slides.

Common mistakes

A colored bead does not cross the tray. It rises and falls over its home mark.
The pulse is not the beads traveling. The disturbance travels, and the beads stay.
This is not the flow tank. There the ink is carried away. Here the beads stay.

Try this

Watch the orange bead, then the blue one. Hit Single pulse. Which bead rises first? Each colored bead should settle back on its home mark. Click a bead to poke it. The ring spreads. That bead stays put. Raise Coupling so neighbors pull harder. The pulse crosses sooner. Raise Damping. The pulse dies on the way.

Coupling 0.48 Damping 0.16 Tempo 0.70

Pulse travels · beads stay

Specimen 08 — Buoyancy

The fluid pushes up.

Buoyancy is the upward push from a fluid. These blocks are the same size, and density decides which one floats and which one sinks.

Note — buoyancy is that upward push. Same size: more matter sinks.

Buoyancy is the upward push from the fluid.

These blocks are the same size. Warm is wood. Pale is the one you set. Gray is metal.

Density is how much matter is in that size. Less than the fluid, and the block floats. More, and it sinks.

The yellow arrow is the push up. It grows as more of the block goes under. The orange arrow is the weight.

Oil has less matter than water. A block that floats in water can sink in oil.

In the world

A naval architect shapes a hull so the ship pushes aside a weight of water equal to the ship's own weight. A scuba instructor shows a diver how to add or release air so the water's upward push matches the diver and the diver can hover. A hot-air balloon pilot heats the air in the balloon until that air has less matter in the same size than the cool air outside, and the balloon rises.

Common mistakes

The blocks are not different sizes. Density, not size, decides float or sink.
The yellow arrow is not the weight. It is the push up. The orange arrow is the weight.
A block that floats in water does not have to float in oil. Oil has less matter than water.

Try this

Press Drop. Wood stays high. Metal goes to the floor. Set the pale block to Wood, then to Metal. Switch Water to Oil and watch which blocks still float.

Density 0.74 Fluid 1.00

Same size · float or sink

Specimen 09 — Viscosity

The thick liquid gives slowly.

Viscosity is how strongly a liquid resists flowing. The same ball falls quickly through a thin liquid and more slowly through a thicker one.

Note — same balls, same drop. A thicker liquid resists the fall.

Viscosity is how strongly a liquid resists flowing. A thick liquid gives slowly. A thin liquid gives easily.

Both balls match. They drop from the same height, and gravity is the same push. The left column stays thin, so that ball falls through quickly.

The right column follows the slider. The number is how many times thicker it is than the left. Raise it, and the same ball sinks more slowly.

In the world

A paint chemist sets the thickness of a coating so it levels smooth on a wall and does not sag into drips. A lubrication engineer chooses an oil thick enough to protect metal parts, and thin enough that an engine does not waste power pushing through it. A sauce cook works the same way with a glaze: thick enough to coat the food, and thin enough to pour.

Common mistakes

The balls are not different weights. They match, and gravity is the same push.
A thicker liquid does not stop the ball. It gives more slowly.
Thin and honey are not two different drops. They are the same drop in different liquids.

Try this

Press Drop. The balls leave together, then the liquid decides. Which one reaches the bottom first? Set Thin and drop again — they should nearly match. Choose Honey and drop once more. Same push. The thick liquid gives slowly.

Viscosity 14.0

Same drop · thicker resists

Specimen 10 — Capillary action

The narrow path climbs higher.

Capillary action is a liquid climbing a narrow wettable path against gravity. The same liquid climbs higher in a narrower tube.

Note — same liquid, same gravity. A narrower opening climbs higher.

Capillary action is a liquid climbing a narrow wettable path against gravity. The liquid's skin pulls along the wall. The wall pulls the liquid up with it.

This dish holds one liquid. Three glass tubes stand in it. The left tube is wide. The right tube is narrow. Nothing else is different.

The middle tube follows the width control. The number is how many times wider that opening is than the narrow tube. A wider opening climbs less. A narrower opening climbs higher.

In the world

A soil scientist watches water climb the narrow pores between soil grains, lifting moisture toward the roots. A textile engineer dyes cloth by wicking: the tight spaces between fibers pull the color along the fabric. A florist counts on the same climb when a cut stem drinks from a vase, because water rises through the narrow tubes inside the plant.

Common mistakes

The tubes do not hold different liquids. One liquid climbs all three.
A wider opening does not climb higher. A narrower opening does.
The climb is not a current. The skin and the wall pull the liquid up against gravity.

Try this

Press Climb. Watch the liquid rise out of the dish. Which tube ends highest? Choose Wide and press Climb again. The middle tube should stay low, near the wide one on the left. Choose Narrow and climb once more. The middle tube should finish high, near the thin one on the right. Same liquid, same gravity. The opening width decides.

Width 2.2

Narrow climbs · wide stays low

Specimen 11 — Diffusion

The dye spreads. The water stays.

Diffusion is matter spreading from a crowded place into emptier ones, with no current to carry it. The dye wanders through still water, and the water stays put.

Note — the water is still. Crowded dye still wanders into empty water.

Diffusion is matter spreading from a crowded place into emptier ones. It does not need a wind or a current.

This dish holds still water. A drop of dye starts crowded on the left. Nothing carries it. The color still spreads. The pale marks in the water stay put.

Warm water lets the dye wander faster. Cool water lets it wander more slowly. The Spread slider is that same choice. A higher number is warmer water. The water does not flow either way. That is different from the flow tank, where a current carries the ink downstream.

In the world

A perfume chemist watches scent molecules leave a concentrated drop and spread through still air. A food scientist designs how a dye or a flavor moves through a gel when nothing is stirring it. A pharmaceutical scientist studies how a medicine spreads through tissue, from a crowded spot into the cells around it.

Common mistakes

The dye does not need a current. It spreads through still water.
The pale marks in the water do not slide. The dye wanders, and the water stays.
Warm and cool do not start a flow. They only change how fast the dye wanders.

Try this

Press Drop dye. Watch the color leave the crowded spot and reach the pale marks. Those marks do not slide. Choose Cool and drop again. The same dye should take longer to spread. Choose Warm and drop once more. The water stays still both times. Only the wandering changes speed.

Spread 1.00

Still water · dye spreads

Specimen 12 — Non-Newtonian

The same mix. The rate changes it.

A non-Newtonian liquid does not keep one thickness. This mix flows under a slow push and firms up under a hard hit.

Note — press slowly and this mix flows. Hit it hard and it holds.

A non-Newtonian liquid does not keep one thickness. This pale mix is in the style of cornstarch and water. A slow push lets it flow. A hard hit makes it firm.

The dish holds one liquid the whole time. A slow poke sinks and leaves a wide dimple. A hard poke meets a surface that resists, and that small dent holds for a moment. A ball lowered slowly sinks in. The same ball, dropped fast, stays on top.

That is different from an ordinary thick liquid, like the honey column in specimen 09. A thick liquid of that kind stays thick whether you go slow or fast. This mix does not. The rate of the push changes how it feels.

In the world

A body-armor engineer designs pads that stay soft while a person walks, then stiffen when a strike lands. A sports-shoe designer uses a foam that gives under a slow step and firms up on impact. A process engineer running an industrial mixer has to know when a slurry will seize: the same mix pours when the blades turn slowly, and locks up when the shear gets high.

Common mistakes

This mix does not stay one thickness. A slow push flows, and a hard hit holds.
A hard poke is not a different material. It is the same mix, pushed faster.
This is not an ordinary thick liquid. Honey stays thick whether you go slow or fast.

Try this

Choose Slow poke and watch the dowel sink into a wide dimple. Choose Hard poke and watch the same mix stop the dowel. Then choose Slow fall and watch the ball sink. Choose Fast drop and watch that ball stay on top and roll. You can also press the mix yourself. Hold for a slow push, or tap quickly for a hard one.

Rate 0.20

Slow push sinks · a hard hit holds

Specimen 13 — Pressure with depth

Deeper water pushes harder.

In a still liquid, pressure rises with depth. The same liquid pushes harder on a deeper panel than on one near the surface.

Note — same liquid, same density. Only the depth changes the push.

In a still liquid, pressure rises with depth. Water near the bottom pushes harder on the wall than water near the top.

This tank holds one liquid. Three soft panels sit on the side wall. The deep panel bulges more, and it glows brighter, because the push there is stronger.

The probe is a movable panel. Near the surface its push stays small. Beside the deep panel it bulges to match. Lower the fill and every panel eases off, because there is less water above it.

In the world

A scuba instructor explains ear squeeze: as a diver goes deeper, the water pushes harder on the ears, and the diver has to equalize. A dam engineer sizes a wall for deeper water, because the push on the concrete grows from the top of the reservoir down to the base. A submarine designer checks the hull load at each depth, since the same hull feels a harder squeeze the farther it travels under the surface.

Common mistakes

The deep panel is not a different liquid. The same liquid pushes harder deeper down.
The probe does not change the pressure. It shows the push at that depth.
Lowering the fill does not leave the push the same. There is less water above each panel, so the push eases off.

Try this

Choose Shallow and look at the probe beside the top panel. It barely bulges. Choose Deep and watch that same probe swell and brighten next to the bottom panel. Then lower Fill and watch the deep panel relax as the water line drops.

Depth 0.50 Fill 0.94

Deeper means a harder push

For teachers

Short objectives, one classroom loop, and how the lab maps to shop practice and intro physics.

Learning objectives

Say that a traveling wave moves energy while the medium oscillates in place.
Point to a float and show that it does not travel with the crest.
Explain tension as a pull shared by neighboring parts of a cloth.
Contrast flow, which carries material, with a wave, which does not.
Describe surface tension as the pull in a liquid's skin, and contrast a beaded drop with one that wets out.
Show that a soft body changes shape under a force, stays one connected piece, and keeps about the same amount of material.
Name the medium as the stuff a wave moves through, and show that a particle stays near its home while the disturbance travels.
Name buoyancy as the upward push from the fluid, and show that same-size blocks float or sink by density.
Explain viscosity as how strongly a liquid resists flow, and show that the same ball, dropped from the same height, falls more slowly in a thicker liquid.
Explain capillary action as a liquid climbing a wettable path against gravity, and show that a narrower opening climbs higher than a wider one when the liquid and gravity stay the same.
Explain diffusion as matter spreading from a crowded place into emptier ones even when the liquid is still, and contrast that with flow, which carries material.
Explain that a shear-thickening liquid changes with the rate of the push, flowing when pressed slowly and firming when struck, and contrast that with an ordinary thick liquid that stays thick at any speed.
Explain that pressure in a still liquid increases with depth, so the same liquid pushes harder on a deeper wall than on a shallow one.

10-minute classroom activity

1) Specimen 01: pick one float. Does it cross the tank? 2) Drop a stone and sketch the ring. 3) Specimen 02: drag once and name what the neighbors do. 4) Specimen 03: follow one ink drop. Write one sentence on how flow differs from the wave. 5) Specimen 05: choose Bead, poke the drop, and watch the skin pull it round. Switch to Wet out. Sketch both shapes. Name surface tension as that pull. 6) Specimen 06: poke the jelly and hold. Point to a colored bit and to a side that swelled. The bit stayed in the body. Let go, then drop the block. Sketch the squash and the climb back. Name stiffness as the pull back, and damping as what quiets the wobble. 7) Specimen 07: pick one colored bead. Send a single pulse. Does the bead cross the tray, or only rise and fall? Say how that differs from the ink. 8) Specimen 08: press Drop. Say which block floats and which sinks. Switch Water to Oil. Name what changed. 9) Specimen 09: press Drop. The balls leave together. Which column finishes first? Set Honey and drop again. Name what stayed the same. 10) Specimen 10: press Climb. Which tube ends highest? Set the middle tube to Wide and climb again, then set it to Narrow and climb once more. Say what stayed the same. 11) Specimen 11: press Drop dye. Does the color ride a current, or spread while the pale marks stay put? Set Cool and drop again, then set Warm and drop once more. Say what the water did both times. 12) Specimen 12: choose Slow poke, then Hard poke. Sketch both marks. The liquid did not change. The speed of the push did. Then try Slow fall and Fast drop, and say which ball sinks. 13) Specimen 13: look at the three panels and sketch which one bulges most. Choose Shallow, then Deep, and say what the probe does. Lower Fill and say why the push gets smaller.

Shop & continuum map

Ripple tanks, flags and shade cloth, wind on a loose cover, ink in a flume, a bead of water on wax paper, the same water wetting clean glass, and a block of gelatin or a foam pad you can push without tearing apart. A tray of beads, or a line of people doing the wave, shows the medium. A wood block and a metal block in one tank: the fluid pushes up, and density decides float or sink. A falling-ball check, the way a coatings bench compares thin paint with a thick one. A dish of water with a wide tube and a narrow one, the way moisture climbs a soil pore. A drop of food coloring spreading in a still dish. A tray of cornstarch and water that firms up under a fast hit. A tank wall that takes a harder push near the bottom. Useful before anyone says “partial differential equation.”

Intro physics map

Transverse waves, wavelength and tempo, damping, tension in a membrane, advection versus wave motion, surface tension — bead versus wet-out — and a soft body whose shape changes while its volume stays about the same. The medium is the stuff a wave moves through. Buoyancy and density — float versus sink. Viscosity — the same weight, a slower fall when the liquid is thicker. Capillary action — the same liquid climbs higher in a narrower wettable path. Diffusion — dye spreads through still water with no current. Shear thickening — the same liquid flows under a slow push and resists a fast one. Hydrostatic pressure — the push in a still liquid grows with depth.