Tag Archives: science

Blind testing of clothes

Inspired by blind taste testing, manufacturers’ claims about clothes could be tested by subjects blinded to what they are wearing. The test would work as follows. People put clothes on by feel with their eyes closed or in a pitch dark room and wear other clothes on top of the item to be tested. Thus the subjects cannot see what they are wearing. They then rate the comfort, warmth, weight, softness and other physical aspects of the garment. This would help consumers select the most practical clothing and keep advertising somewhat more honest than heretofore. For example, many socks are advertised as warm, but based on my experience, many of them do not live up to the hype. I would be willing to pay a small amount for data about past wearers’ experience. Online reviews are notoriously emotional and biased.

Some aspects of clothes can also be measured objectively – warmth is one of these, measured by heat flow through the garment per unit of area. Such data is unfortunately rarely reported. The physical measurements to conduct on clothes require some thought, to make these correspond to the wearing experience. For example, if clothes are thicker in some parts, then their insulation should be measured in multiple places. Some parts of the garment may usually be worn with more layers under or over it than others, which may affect the required warmth of different areas of the clothing item differently. Sweat may change the insulation properties dramatically, e.g. for cotton. Windproofness matters for whether windchill can be felt. All this needs taking into account when converting physical measurements to how the clothes feel.

Keeping an open mind and intellectual honesty

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„Keep an open mind” is often used as an argument against science, or to justify ignoring evidence more broadly. Let’s distinguish two cases of keeping an open mind: before vs after the evidence comes in. It is good to keep an open mind before data is obtained – no hypothesis is ruled out. In reality, all possibilities have positive probability, no matter how great the amount and quality of information, so one should not dogmatically rule out anything even given the best evidence. However, for practical purposes a small enough probability is the same as zero. Decisions have to be made constantly (choosing not to decide is also a decision), so after enough scientific information is available, it is optimal to make up one’s mind, instead of keeping it open.
Intellectually honest people who want to keep an open mind after obtaining evidence would commit to it from the start: publicly say that no matter what the data shows in the future, they will ignore it and keep an open mind. Similarly, the intellectually honest who plan to make up their mind would also commit, in this case to a policy along the lines of „if the evidence says A, then do this, but if the evidence says B, then that”. The latter policy resembles (parts of) the scientific method.
The anti-science or just intellectually dishonest way of “keeping an open mind” is to do this if and only if the evidence disagrees with one’s prior views. In other words, favourable data is accepted, but unfavourable ignored, justifying the ignoring with the open mind excuse. In debates, the side that runs out of arguments and is about to lose is usually the one who recommends an open mind, and only at that late stage of the debate and conditional on own weak position. Similarly, “agreeing to disagree” is mostly recommended intellectually dishonestly by the losing side of an argument, to attempt to leave the outcome uncertain. This is an almost logically contradictory use of “agreeing to disagree”, because it is mathematically proven that rational agents putting positive probability on the same events cannot agree to disagree – if their posterior beliefs are common knowledge, then these must coincide.

Seasonings may reduce the variety of diet

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Animals may evolve a preference for a varied diet in order to get the many nutrients they need. A test of this on mice would be whether their preference for different grains is negatively autocorrelated, i.e. they are less likely to choose a food if they have eaten more of it recently.

Variety is perceived mainly through taste, so the mechanism via which the preference for a varied diet probably operates is that consuming a substance repeatedly makes its taste less pleasant for the next meal. Spices and other flavourings can make the same food seem different, so may interfere with variety-seeking, essentially by deceiving the taste. A test of this on mice would flavour the same grain differently and check whether this attenuates the negative autocorrelation of consumption, both when other grains are available and when not.

If seasonings reduce variety-seeking, then access to spices may lead people to consume a more monotonous diet, which may be less healthy. A test of this hypothesis is whether increased access to flavourings leads to more obesity, especially among those constrained to eat similar foods over time. The constraint may be poverty (only a few cheap foods are affordable) or physical access (living in a remote, unpopulated area).

A preference for variety explains why monotonous diets, such as Atkins, may help lose weight: eating similar food repeatedly gets boring, so the dieter eats less.

Ways in which an eater can get negative calories from food

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There are at least four ways in which an eater may have less energy and nutrients after consuming a food: mechanical, chemical, physical and biological. The mechanical way is that chewing and other parts of digestion take energy, so if a food requires serious mastication and contains few calories, then more energy may be spent than absorbed. This has been claimed for raw celery.
Chemically, one food may react with another in a way that makes one or both of them less digestible. The less effective absorption reduces the nutrients obtained compared to not eating the second reactant. The chemical pathway to inefficient digestion may have multiple steps. For example, ascorbic acid leaches calcium from the body, and calcium is required for the absorption of vitamin D, so eating more citrus fruits may indirectly reduce one’s vitamin D levels.
When calculating the calorie content of food, indigestible fibre is subtracted from carbohydrates before adding up the energy obtained from carbohydrates, fats and proteins. However, if fibre reduces the absorption of calories (in addition to its known reduction of the absorption iron, zinc, magnesium, calcium and phosphorus), then the food’s bioavailable calorie content is less than that obtained by simply subtracting the fibre. To derive the correct calorie content, the fibre should then have negative weight in the calculation, not zero. This difference may explain why in Western countries, a high-fibre diet predicts better health in multiple dimensions in large prospective studies (Nurses’ Health Study, Framingham Heart Study), controlling for calorie intake, lifestyle and many other factors. If the calorie absorption is overestimated for people eating lots of fibre (because the calorie intake is larger than the absorption), then their predicted health based on the too high calorie estimate is worse than their actual health. This is because most people in Western countries overeat, so eating less improves health outcomes. If the predicted health is underestimated, then the high-fibre group looks unusually healthy, which is attributed to the beneficial effects of fibre, but may actually be due to absorbing fewer calories.
A food may chemically break down tissues, e.g. bromelain and papain, from fresh pineapple and papaya respectively, denature meat proteins, so cause mouth sores. Rebuilding the damaged tissue requires the energy and nutrients, the quantity of which may exceed that absorbed from the food.
Chemically causing diarrhea reduces the time that foods (including the laxative agent) spend in the gut, thus reduces nutrient absorption.
Stimulants like caffeine speed up metabolism and cause greater energy expenditure, but may give zero calories themselves, resulting in a net negative caloric balance.
Just like chemical damage, physical injury to the body necessitates spending calories and nutrients for tissue repair. For example, scratchy food (phytoliths, bran) may cause many microscopic wounds to the digestive tract.
Cold food requires the body to spend energy on heating, so if the calorie content is small, then the net energy obtained is is negative. Examples are ice cubes and cold water.
A food substance may physically partially block the absorption of another, for example a gelling agent (methylcellulose, psyllium husks) may turn a juice into a gel in the gut and thereby reduce its absorption. Based on my personal experience, psyllium husks gel liquid feces, thus effectively reducing diarrhea. Mixing psyllium husks with carrot juice and with asparagus powder dissolved in water before consuming them during the same meal results in the excretion of separated faint orange and green gels somewhat distinct from the rest of the feces (photos available upon request, not posted to keep the blog family-friendly). This is suggestive evidence that the gelling agent both kept the juices from mixing in the gut and reduced the absorption of the colourful compounds by keeping the juice in the centre of the gel away from the intestinal wall.
Biologically, a food may reduce the nutrients available to the organism by causing infection, the immune response to which requires energy and depletes the body’s reserves of various substances. Infection may lead to diarrhea, although the mechanism is chemical, namely the toxins excreted by the microbes. Infection with helminths (intestinal worms) that suck blood through the wall of the gut requires the replenishment of blood cells, which uses up calories, protein and iron.
If the food takes a long time to chew or is bulky, then chemical and electrical signals of satiation are sent from the gastrointestinal tract to the the appetite centre of the brain. These signals reduce the desire to eat, thus decrease calorie intake.

Bad popular science books

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There is a class of books that is marketed as popular science, but have the profit from sales as their only goal, disregarding truth. Easily visible signs of these are titles that include clickbait keywords (sex, seduction, death, fear, apocalypse, diet), controversial or emotional topics (evolution, health, psychology theories, war, terrorism), radical statements about these topics (statements opposite to mainstream thinking, common sense or previous research), and big claims about the authors’ qualifications that are actually hollow (PhD from an obscure institution or not in the field of the book). The authors typically include a journalist (or writer, or some other professional marketer of narratives) and a person that seems to be qualified in the field of the book. Of course these signs are an imperfect signal, but their usefulness is that they are visible from the covers.
Inside such a book, the authors cherry-pick pieces of science and non-science that support the claim that the book makes, and ignore contradicting evidence, even if that evidence is present in the same research articles that the book cites as supporting it. Most pages promise that soon the book will prove the claims that are made on that page, but somehow the book never gets to the proof. It just presents more unfounded claims.
A book of this class does not define its central concepts or claims precisely, so it can flexibly interpret previous research as supporting its claims. The book does not make precise what would constitute evidence refuting its claim, but sets up “straw-man” counterarguments to its claim and refutes them (mischaracterising the actual counterarguments to make them look ridiculous).
Examples of these books that I have read to some extent before becoming exasperated by their demagoguery: Sex at dawn, Games people play.

Heating my apartment with a gas stove

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There is no built-in heating system in my Australian-standard un-insulated apartment, and the plug-in electric radiators do not have enough power to raise the temperature by a degree. In the past two winters, I used the gas stove as a heater. It is generally unwise to heat an enclosed space without purpose-built ventilation (such as a chimney) by burning something, because of the risk of CO poisoning. Even before CO becomes a problem, suffocation may occur because the CO2 concentration rises and oxygen concentration falls. Therefore, before deciding to heat with a gas stove, I looked up the research, made thorough calculations and checked them several times. I also bought a CO detector, tested it and placed it next to the gas stove. The ceiling has a smoke alarm permanently attached, but this only detects soot in the air, not gases like CO.
For the calculations, I looked up how much heat is produced by burning a cubic metre or kilogram of CH4 (natural gas), how much the temperature of the air in the apartment should rise as a result, how much CO2 the burning produces, and what the safe limits of long-term CO2 exposure are.
The energy content of CH4 is 37.2 MJ/m3, equivalently 50-55.5 MJ/kg. A pilot light of a water heater is estimated to produce 5.3 kWh/day = 20 MJ/day of heat, but a gas stove’s biggest burner turned fully on is estimated to produce 5-15 MJ/h, depending on the stove and the data source.
The chemical reaction of burning natural gas when oxygen is not a limiting factor is CH4 +2*O2 =CO2 +2*H2O. The molar masses of these gases are CH4=16 g/mol, O2=32 g/mol, CO2=44 g/mol, H2O=18 g/mol, air 29 g/mol. One stove burner on full for 1 hour uses about 0.182 kg =0.255 m3 of CH4 and 0.364 kg of O2, which depletes 1.82 kg = 1.52 m3 of air. The burning produces 2.75*0.182 = 0.5 kg = 0.41 m3 of CO2. The CO2 is denser than air, which is why it may remain in the apartment and displace air when the cracks around the windows are relatively high up. On the other hand, the CO2 also mixes with the air, so may escape at the same rate. Or alternatively, the CO2 is hot, so may rise and escape faster than air. For safety calculations, I want to use a conservative estimate, so assume that the CO2 remains in the apartment.
The volume of the apartment is 6x5x2.5 m =75 m^3. The density of air at room temperature is 1.2 kg/m^3, thus the mass of air in the apartment is 90 kg. The specific heat of air is 1005 kJ/(kg*K) at 20C. The walls and ceiling leak heat, thus more energy is actually needed to heat the apartment by a given amount than the calculation using only air shows. It takes 900 kJ of heat to raise the temperature of the air, not the walls, by 10C (from 12C to 22C). This requires 9/555 kg = 9/(16*555) kmol of CH4 with estimated energy density 55500 kJ/kg. Burning that CH4 also takes 9/(8*555) kmol of O2 and produces 9*11/(4*555) kmol = 9/200 kg of CO2.
The normal concentration of CO2 in outside air is 350-450 ppm. Estimate the baseline concentration in inside air to be 1/2000 ppm because of breathing and poor ventilation. Adding 1/2000 ppm from heating, the CO2 concentration reaches 1/1000 ppm. This is below the legal limit for long-term exposure.
CO is produced in low-oxygen burning. As long as the CO2 concentration in the air is low and the oxygen concentration high, the risk of CO poisoning is small.
For the actual heating, I first tested running the smallest burner all day while I was at home, and paid attention to whether I felt sleepy and whether the air in the apartment smelled more stale than outside or in the corridor. There seemed to be no problems. For nighttime heating, I started with the smallest burner in the lowest setting, similarly paying attention to whether the air in the morning smelled staler than usual and whether I felt any different. Because there were no problems, I gradually increased the heating from week to week. The maximum I reached was to turn on the largest burner to less than half power, and one or two smaller burners fully. Together, these burners produced much less heat than the largest burner on full, as could be easily checked by feel when standing next to the stove. At night, the stove prevented the temperature in the apartment from dropping by the usual 2C, but did not increase it. The CO2 produced was probably far less than the bound I calculated above by assuming a 10C increase in temperature. Empirically, I’m still alive after two winters of letting the gas stove run overnight.

How superstition grows out of science

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Priests in Ancient Egypt could predict eclipses and the floods of the Nile by observing the stars and the Moon and recording their previous positions when the events of interest happened. The rest was calculation, nothing magical. Ordinary people saw the priests looking at the stars and predicting events in the future, and thought that the stars magically told priests things and that the prediction ability extended to all future events (births, deaths, outcomes of battles). The priests encouraged this belief, because it gave them more power. This is one way astrology could have developed – by distorting and exaggerating the science of astronomy. Another way is via navigators telling the latitude of a ship using the stars or the sun. People would have thought that if heavenly bodies could tell a navigator his location on the open sea, then why not other secrets?
Engineers in Ancient Rome calculated the strength of bridges and aqueducts, and estimated the amount of material needed for these works. Ordinary people saw the engineers playing with numbers and predicting the amount of stones needed for a house or a fort. Numbers “magically” told engineers about the future, and ordinary people thought this prediction ability extended to all future events. Thus the belief in numerology could have been born.
When certain plants were discovered to have medicinal properties against certain diseases, then swindlers imitated doctors by claiming that other natural substances were powerful cures against whatever diseases. The charlatans and snake oil salesmen distorted and exaggerated medicine.
Doctors diagnosed diseases by physical examination before laboratory tests were invented. Thus a doctor could look at parts of a person’s body, tell what diseases the person had, and predict the symptoms that the person would experience in the future. Exaggerating this, palm readers claimed to predict a person’s future life course by looking at the skin of their palm.
In the 20th century, some medicines were discovered to be equally effective at somewhat lower doses than previously thought. Then homeopathy exaggerated this by claiming that medicines are effective when diluted so much that on average not a single molecule of the drug remains in the water given to the patient.
In all these cases, superstition only adds bias and noise to scientific results. Science does not know everything, but it is a sufficient statistic (https://en.wikipedia.org/wiki/Sufficient_statistic) for superstitious beliefs, in the sense that any true information contained in superstition is also contained in science. Nothing additional can be learned from superstition once the scientific results are known.

Scientific thinking coordination game

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If most people in a society use the scientific method for decision-making, then telling stories will not persuade them – they will demand evidence. In that case, bullshit artists and storytellers will not have much influence. It is then profitable to learn to provide evidence, which is positively correlated with learning to understand and use evidence. If young people respond to incentives and want to become influential in society (get a high income and social status), then young people will learn and use the scientific method, which reinforces the demand for evidence and reduces the demand for narratives.
If most people are not scientifically minded, but believe stories, then it is profitable to learn to tell stories. The skilled storytellers will be able to manipulate people, thus will gain wealth and power. Young people who want to climb the social and income ladder will then gravitate towards narrative fields of study. They will not learn to understand and use evidence, which reinforces the low demand for evidence.
Both the scientific and the narrative society are self-reinforcing, thus there is a coordination game of people choosing to become evidence-users or storytellers. Note that using the scientific method does not mean being a scientist. Most researchers who I have met do not use science in their everyday decisions, but believe the stories they read in the media or hear from their friends. I have met Yale PhD-s in STEM fields who held beliefs that most people in the world would agree to be false.
One signal of not thinking scientifically is asking people what the weather is like in some place one has not visited (I don’t mean asking in order to make small talk, but asking to gain information). Weather statistics for most places in the world are available online and are much more accurate than acquaintances’ opinions of the weather. This is because weather statistics are based on a much longer time series and on physically measured temperature, rainfall, wind, etc, not on a person’s guess of these variables.

Ideas for popular science experiments

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There are many science fair experiment ideas online. The following may be repetitions.
A windmill connected to an electric generator, which is connected to a lightbulb (small dimmable is best). Blow on the windmill to turn the light on. A separate generator similar to the one attached to the windmill, which can be cranked by hand to turn on the lightbulb. An electric fan that can blow on the windmill, with power consumption at the fan and power production at the windmill measured and displayed. This explains efficiency losses in power generation.
Pressure of light. A piece of paper attached vertically on a platform that can rotate at low friction. On one side of the rotation axis, the paper is painted black, on the other, it is white. Reversed on the opposite side of the paper. Transparent dome over the setup to prevent air currents interfering. Shining a light on the paper makes it rotate, because the pressure on one side is greater. The rotating platform can be a polystyrene disk floating in water.
Pulleys and gear ratios. A bicycle with gears, rear wheel removed, but axle in place. Rope attached to axle, weight to rope. Rotating the pedals lifts the weight. Different gears require different number of rotations to lift the weight to a given height, but the more rotations needed, the less force needed for the rotation. Explain why low gears on a bike should be used when starting and on uphills, but high gears on downhills.
Moving pulleys: the distance the rope has to be pulled becomes longer, but the force required to pull becomes smaller to lift a given weight a given distance.
Friction in braking. Several bicycle wheels with brakes attached. Some rims are dry, some wet, some oiled. Feel the braking force required to stop each. To provide the force that the brakes must counter, a weight can be attached to each wheel. Rotate the weight away from the lowest point of the wheel and try to use the brakes to prevent the weight from sinking to the bottom again.
Friction in accelerating. Old bicycle. Rotate the pedals to accelerate the rear wheel to a given speed (measured with a bicycle speedometer) when the chain is dry, or oiled, or sand is poured on the chain. Feel the different difficulty depending on the condition of the chain. Several bikes is better, so the chains in different condition can be compared.
Friction and heat: a fire drill. Rotate a sharp stick in a hole in a piece of wood – the hole blackens and starts to smoke.
Ball bearings. Stack two blocks, put weight on the top one, try to rotate the bottom one. Now the same blocks with two ball bearings, one between the ground and the bottom bearing and the other between the two blocks. Much easier to rotate the bottom block. Explain how rolling friction is smaller than dragging friction. Friction proportional to pressure. Friction related to surface area.
Tire pressure and friction. Bicycle wheels (preferably with identical rims, hubs and spokes) with different width tires on them. Measure the friction of the tires by the force required to rotate them at a given speed on some surface, with the tire bearing weight. A stationary bicycle trainer can be used. Which tire width gives the lowest friction? Research shows that 22-23 mm tires have the lowest friction under the weight of an adult cyclist. Deflate the tire, measure the friction. Inflate, measure the friction. Which inflation pressure gives the lowest friction? Research shows that it is not the maximal pressure, unless the surface on which the wheel rotates is very smooth.
Mining and ores. Different rock samples of various ores. Panning for “gold”: try to find a shiny grain hidden in a quantity of mud or sand.
Solvents. Pebbles or small toys mixed in sugar paste or syrup, which is then dried into blocks. Use water to dissolve the sugar and discover what is inside the blocks.
Leidenfrost effect. Air hockey table with air being pumped under the hockey puck. Compare to droplets of liquid nitrogen rolling on a warm surface. Compare to pancakes riding on the steam bubbles under them on a hot pan.
Bridge of spaghetti. Dry spaghetti can be attached to each other with small balls of dough (flour mixed with water). Then bake the spaghetti-and-dough construction to harden the dough. Check how much weight the bridge can carry. Compare the breaking weight for a bridge (triangularly connected spaghetti that look like high-voltage power line towers) to the breaking weight for a bunch of horizontal spaghetti. The bridge can also be made by glueing matches or toothpicks.
Detergents. Lightly grease some cloth that normally absorbs water. Put water on top of that cloth – droplets form and nothing leaks through. Put water in a cloth bag and show that it does not leak. Compare to ungreased cloth that lets water through. Add detergent to the water on the greasy cloth. With the right coarseness of cloth, amount of grease and detergent, the water should start leaking through.
A burner under a thin paper box filled with water. The paper does not burn and does not become soggy, so the water does not leak through.
Absorption and radiation. Heat lamp shining on a black and white rock. Which becomes warm first? Now heat the rocks by contact, e.g. in warm water. Which rock cools down first? Infrared laser thermometer may help confirm temperatures. Or an ordinary thermometer inserted in a hole drilled in the rock.
Hot air rises. A nonflammable parachute rises above a candle. The parachute could be of thin tinfoil. It should have a light weight attached below the canopy to keep it upright. A tinfoil pinwheel can be held above the candle – it starts to rotate in the updraft of hot air.
3D printing by hand. Mud dripped from a hand onto sand or another surface that lets water through easily. The water soaks out of the droplets of mud that hit the surface, leaving a series of solid bumps of mud. Drop another droplet of mud on top of the bumps – water soaks out again, the bumps are now higher. Use this technique to build walls, castles etc.
Internal combustion engine. A rotating shaft with two pistons attached (can be made of wood or some other cheap, light, strong enough material). A balloon under each piston. If two people rapidly inflate and let deflate the balloons in the right sequence, then the shaft starts to rotate. Also a great party game – which couple gets their motor running fastest? The balloons can also be inflated by a hand pump, but fast and well-timed deflation is then a problem. One end of a long snakelike balloon can be under the piston, the other end squeezed and released by hand. The right sequence of squeeze and release can make the shaft rotate. One person can hold two long balloons, so can rotate the engine alone. A single piston is enough to rotate a wheel if attached to the rim – this is the arrangement in some old steam locomotives and foot-pedalled Singer sewing machines.
Steam power. Electric kettle boiling water, with a small windmill above the spout. The steam rising from the kettle rotates the windmill. Measure the power generated by the windmill and compare to the electricity required to heat the kettle.
Electric motor. Hand generator produces electricity, which is led by wires to an electric motor, which starts to rotate. Or the electricity is led to a coil with a permanent magnet inside. The magnet starts to move when the hand generator is cranked. With the right speed of cranking, an alternating current can make the magnet rotate.
Water mill. Pour the water at the top of a halfpipe. A waterwheel in the halfpipe starts to rotate in the flow. The rotation can drive a small generator which lights up a tiny lightbulb.
Archimedes’ screw. A helix in a pipe that is slightly tilted from horizontal can be rotated to pump water up the pipe.
Connected vessels. Two cups of water at different heights linked by a bent drinking straw. Suck the bottom of the straw to get water over the hump in the straw. Then water will start to flow from the top cup to the bottom, initially going uphill in the straw.
A bit of charcoal dropped in a vial of pure oxygen spontaneously catches fire. The oxygen can be generated at the bottom of the vial using hydrogen peroxide and a drop of blood. Steel wire in a pure oxygen environment rusts rapidly enough to be observed in a single experiment.
Bimetal thermostat. Two strips of different metals glued, soldered or riveted together at the ends. Heat the joined strip with a hair dryer – it bends to one side. The bent strip can touch a contact and switch something on or off, for example the hair dryer. A feedback loop can be constructed: if the joined metal strip gets cold enough, then it switches on the hair dryer, which heats the strip, which then switches off the hair dryer.
Tracks vs wheels. Tracked and wheeled model vehicles driving in a sandbox and on a smooth surface. The vehicles are the same weight, have the same motor and battery. Compare performance going up a sandhill vs racing on a smooth surface.
A spinning top to illustrate gyroscopes and self-stabilising.
Degrees of freedom of movement. Mechanical devices that illustrate the 3 translation and 3 rotation possibilities by allowing some of them, but not others. For example the serial gimbal, 3-axis gimbal, origami for thick materials (Science 24 Jul 2015: Vol. 349, Issue 6246, pp. 396-400, DOI: 10.1126/science.aab2870), bicycle front fork with shock absorbers, shopping trolley wheel or office chair wheel. For fun, rotate a person on an office chair a few dozen turns, then ask them to walk in a straight line.
Origami: Miura fold, hexaflexagon. Cutting and gluing mathematical objects, e.g. a Mobius strip, a Klein bottle. Math drawing with compass and ruler, e.g. a flower made from 7 interlinked circles of the same diameter. Sierpinsky carpet. Inscribing circles in squares and vice versa.
Boil amaranth in a transparent vessel. The grains dance on the bottom, then form columns, then a goo with large breaking and splattering bubbles.
Water volcano. A small bottle of warm coloured water is dropped in a large transparent vessel containing clear cold water. The coloured water will rise to the top and spread out, like a volcanic ash plume rises in the atmosphere and spreads in a layer.
Twinkling stars and heat mirages. A transparent rectangular vessel of water with points of light behind it. Look through the water: the points do not move. Now heat the water from the bottom: the points of light start to wobble, because warm water currents are rising up and bending the light passing through them.
Refractive index measurement. Water and cooking oil in transparent vessels. One person puts a straight stick at an angle into the liquid – the stick seems to bend at the immersion point. The person points out where they perceive the bottom end of the stick to be. Another person at the side of the vessel measures the angle between the perceived and actual sticks. The difference in angles is different for water than for oil.
Muscles and joints. Ask a person to relax their hand on a table, palm up. Press on the inside forearm and pull it toward the elbow – the 3 smallest fingers bend. Pull the palm towards the wrist – the fingers bend. An excavator’s scoop is moved by pistons like human limbs are moved by muscles – by pulling on the joint on one side or another.
Centrifuge to separate liquids, or solids from a liquid. The low-cost whirligig centrifuge (paperfuge) is described in Nature Biomedical Engineering 1, Article number: 0009 (2017) doi:10.1038/s41551-016-0009 and http://www.nature.com/news/spinning-toy-reinvented-as-low-tech-centrifuge-1.21273 Animal blood or some mixture of liquids and solid flakes can be separated into component liquids and solids by spinning it.
Solar-powered distillation. The 1 square metre device made of polystyrene, paper and charcoal distils about 1 litre of water per hour, as described in http://www.sciencemag.org/news/2017/02/sunlight-powered-purifier-could-clean-water-impoverished Explain capillary action, evaporation and condensation, black material absorbing heat radiation faster.
Passive cooling. Glass beads 8 micrometres in diameter embedded in a polymethylpentene film backed with a thin silver film. The film conducts heat from the surface it sits on and radiates it away in in the other direction. http://www.sciencemag.org/news/2017/02/cheap-plastic-film-cools-whatever-it-touches-10-c
Oil- and water-repellent coating of glass. Cannot be prepared on the spot, but previously fabricated coatings can be demonstrated. Deposit candle soot on glass, then coat with a 25 nanometre silica film by putting the glass in a desiccator with open vessels of tetraethoxysilane and ammonia for 24 hours. Heat to 600C in air for 2 hours. Put in a desiccator with open beaker of semifluorinated silane for 3 hours. Xu Deng et al. “Candle Soot as a Template for a Transparent Robust Superamphiphobic Coating” http://science.sciencemag.org/content/sci/335/6064/67.full.pdf?sid=ca40c018-0715-4d3b-8e36-58c329dea347

Electricity and water analogy. Pouring water down an inclined halfpipe to rotate a water wheel under the bottom of the halfpipe. The water wheel is connected to a winch that can lift a small weight. The height or angle of the halfpipe and the quantity of water can be changed, which lifts the weight at different speeds or can lift a larger weight. The height of the halfpipe is analogous to the potential difference (voltage) and the quantity of water per second to the current (amperage, electrons per second). The water wheel can also be connected to a generator that powers a small dimmable lightbulb. The brightness of the bulb changes with the speed of the water wheel.
Plastic beads in water poured down a halfpipe can demonstrate the measurement of flow per unit of time: the number of beads passing a given point per ten seconds for example.
Ship shape. Make model boat hulls out of some easily worked material, e.g. putty, model clay (hull must be thin to float), cut styrofoam, cardboard taped together and covered with cling film. The styrofoam needs extra weight, for example a piece of sheetmetal pushed through it in the middle to make a keel. The cardboard boat can carry some gravel as ballast. Then each boat gets a motor of equal power, e.g. a propeller powered by a wind-up spring from some toy. Weigh the boats and add ballast as needed to equalise weights. Race the boats to see which hull shape is fastest. To keep the racing boats straight, put them in parallel halfpipes of water, or create swimming pool lanes in a large tub by parallel strings drawn taut on the surface of the water.

Priming the pump. An interesting mechanical device is a piston pump for getting water out of the ground. A piston moves up and down in a vertical pipe open at the top. There is a hole in the side of the pipe from which water can come out. The piston passes above and below the hole as it moves. A dry piston doesn’t pump water up, but pouring some water on the piston (priming the pump) creates a temporary airtight seal around the piston, so pulling the piston up creates a slight vacuum under it, which draws the water up. The water flows out of the hole in the side of the pipe.
Spinning methods and yarn properties. Threads or wires can be spun into yarn by cone spinning, Fermat or dual-Archimedean spinning. With enough twist, the yarn starts to coil like a telephone cord. Folding twisted yarn in two makes the two halves twist around each other – this is how rope is made. Twisted but uncoiled yarn can be coiled in the opposite direction to the twist. Removing the core around which the coiling took place lets the twist and coil cancel – parallel threads result.

Ricequakes as a model of rockfill dam collapse: put puffed rice in a transparent vertical vessel under pressure and let water in from the bottom. The rice starts compacting in sudden collapses, not gradually. Itai Einav and François Guillard “Tracking time with ricequakes in partially soaked brittle porous media” http://advances.sciencemag.org/content/4/10/eaat6961

Capturing water vapour in water beads flowing down vertical cotton threads while the humid air flows up along the threads. The goal is desalination and water purification in general. A Sadeghpour et al 2019 https://advances.sciencemag.org/content/5/4/eaav7662

Soft pneumatic oscillator driven by constant pressure: three cylinders connected a ring, each containing a bistable hemispherical diaphragm. The diaphragm popping to the other side buckles a tube, choking airflow to the next cylinder, which allows its diaphragm to pop back, straightening a tube and allowing airflow. Preston et al. 2019 https://robotics.sciencemag.org/content/4/31/eaaw5496

Blind taste test: compare premium food brands to cheap ones, organic to non-organic, farmers’ market and supermarket produce, fake crabmeat or grape juice to real, different sorts of apples or other fruits, nuts, vegetables, mushrooms. The testers could be blindfolded and audio-record their observations. For written observations, testers could close their eyes while assistants put food pieces in their mouths, then open their eyes for writing. The food pieces should be numbered in advance.

Blind clothing test: compare the warmth of socks, hats, gloves, scarves, the feel of different fabrics. An assistant puts the garment on the blindfolded tester who then audio-records the observations about the feel.

Soft phototactic swimmer based on self-sustained hydrogel oscillator: a hydrogel plate floats on water, has an underwater tail of hydrogel with embedded Au nanoparticles. Light shone on the tail heats the particles, heat bends the tail. The tip of the tail then casts a shadow on the previously illuminated part, which cools and straightens it. Straightening removes the shadow, letting light bend the tail again. Constant light thus causes the tail to oscillate, which propels the swimer away from light. Zhao et al. 2019 https://robotics.sciencemag.org/content/4/33/eaax7112

Delta wing carbon fibre robot launched from water to air by exploding acetylene, then gliding back to water. The explosion forces a water jet out from the reaction chamber through a nozzle. Acetylene produced on board from calcium carbide powder and water. Zufferey et al. 2019 https://robotics.sciencemag.org/content/4/34/eaax7330

Magnetic quadrupoles as building blocks for stable complex shapes. The quadrupoles are made from two magnets placed at a 20-degree angle to each other in a 3D printed square case. Joining the cases with an elastic stick allows the assembly to deform interestingly under magnetic fields. Gu et al. 2019 https://robotics.sciencemag.org/content/4/35/eaax8977

Objects float on the underside of viscous silicon oil or glycerol that is suspended above air using >100Hz vertical vibration. Apffel et al 2020 https://www.nature.com/articles/s41586-020-2643-8

Grooves in a material that swells in water or some other solvent make it bend as thinner parts of the material absorb water faster. Grooved flat pasta dough can be made to take 3D shapes when boiled. Tao et al 2021 https://advances.sciencemag.org/content/7/19/eabf4098

Economics to guide materials science

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There are too many possible materials to test them all, or even simulate by computer. Materials scientists theorize what combinations of elements are likely to yield the desired properties, but still there are too many possibilities. One way to narrow the choice is to use economics.

If the goal of developing a material is to change the world or make money, the benefit of the invention must exceed the cost. The benefit comes from the improved characteristics of the material relative to existing alternatives. What the market is willing to pay for an improvement depends on its size. There may be a theoretical maximum for a property, or its historical rate of increase may be used to forecast the likely improvement. Once an approximate willingness to pay for a unit of the candidate invented material is known, this can be compared with its estimated cost.

Financial firms dealing in commodity futures forecast the prices of chemical elements over the likely commercialization time horizon. Only materials using a combination of elements that is cheap enough are commercially promising. Cheap enough means that the improved material must cost less per unit than the market is willing to pay for it. An expensive element can be used, but only in appropriately tiny quantity. The requirement that the bundle of elements cost less than some bound cuts down on the number of combinations that are worth testing. Similarly, the manufacturing method must be cheap enough, so some methods may be ignored.

The basic cost-benefit analysis is a simple idea, though the benefit estimation may be complicated in practice. Probably the companies producing various materials are already taking the potential cost and benefit of an innovation into account in their R&D, but academic materials scientists perhaps not. If the goal is to advance fundamental science and satisfy one’s curiosity, then the cost of the material may not be an issue. But for the world to use the material, it must be cheap enough.

A practical recommendation is for an application-oriented lab to put up a periodic table with the prices of the elements added. A spreadsheet with the prices of commodities can be used to calculate the cost of a candidate combination for a new material. Testing the candidates should proceed in the order of decreasing “profit” (benefit minus cost of the material). This profit is not necessarily the same as commercial profit, because the benefit may include its whole contribution to society, not just the revenue to the producer.