Tag Archives: education

Ideas for popular science experiments

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.

Teaching and research and division of labour

Universities usually prefer that the same person both teaches and does research. There are some purely teaching or purely research-focussed positions, but these are a minority. Both teaching and research achievements (and service as well) are required for tenure. This runs counter to Adam Smith’s argument that division of labour raises overall productivity. One possible cause is an economy of scope (synergy), meaning that teaching helps with research, or research helps to teach. In my experience, there is no such synergy, except maybe in high-level doctoral courses that focus exclusively on recent research. Revising old and basic knowledge by teaching it does not help generate novel insights about recent discoveries. Complex research does not help explain introductory ideas simply and clearly to beginners.

Another explanation is that universities try to hide their cross-subsidy going from teaching to research. The government gives money mainly for teaching, and if teachers and researchers were different people, then it would be easy for the government to check how much money was spent on each group. If, however, the same person is engaged in both activities, then the university can claim that most of the person’s time is spent teaching, or that their research is really designed to improve their teaching. In reality, teaching may be a minor side job and most of the salary may be paid for the research. This is suggested by the weight of research in hiring and tenuring.

The income of universities mostly comes from teaching, so they try to reduce competition from non-university teachers and institutions. One way is to differentiate their product by claiming that university teaching is special, complicated and research-based, so must be done by PhD holders or at least graduate students. Then schoolteachers for example would be excluded from providing this service. Actually the material up to and including first year doctorate courses is textbook-based and thus cannot consist of very recent discoveries. With the help of a textbook, many people could teach it – research is not required, only knowing the material thoroughly. For example, an undergraduate with good teaching skills who was top of the class in a course could teach that course next semester. Teaching skill is not highly correlated with research skill. The advantage someone who recently learned the material has in teaching it is that they remember which parts were difficult. A person who has known something for a long time probably does not recall how they would have preferred it taught when they first learned it.

Researchers forget the basics over time, because they rarely use these – there are more advanced methods. The foundations are learned to facilitate later learning of intermediate knowledge, which in turn helps with more complicated things and so on up to research level. Similarly in sports, musical performance, sewing, the initial exercises for learners can be quite different from the activity that is the end goal. A sports coach is rarely an Olympic athlete at the same time, so why should a teacher be a researcher simultaneously?

On electric bikes and science news

There is some debate on whether electric-assist bikes are good or bad. The argument on the negative side is that people will stop cycling and bike roads will be taken over by these (electric-)motorized vehicles. On the positive side, the claim is that electric bikes replace motor scooters, cars and public transit, which is good for the environment and perhaps health if people actually pedal their electric bike a bit. To summarize: electric bikes good if replace motor vehicles, electric bikes bad if replace bicycles or walking. It is an empirical question what the substitution sizes are.

There are many calls for scientists to communicate better, engage the public, present their results simply and interestingly etc. Whether more science news and popular science is good or bad depends on what it replaces, just like for electric bikes. If dumbed down entertainment science replaces the rigorous variety, this is bad. If science news replaces brainless news (celebrity gossip, funny animals, speculation on future events), it is good. It is an empirical question to what extent scientists switch to popular topics and crafting press releases if their evaluations rely more on outreach or policy impact. Also a question for the data is which news are left out of print to make room for more science news.

To maximize education of the public, there is a tradeoff between the seriousness of the science presented and the size of the audience. Research article level complexity is accessible to only a few experts. Entertainment is watched by many, but does not educate. The optimum must be somewhere in the middle.

Similarly, difficult courses in a university have few students taking them, but teach those few more than fun and easy subjects. The best complexity level is somewhere between standup comedy and a research seminar.

Coordination game in choosing a university

The ranking of universities is very stable over time (http://m.chronicle.com/article/Rank-Delusions/189919) regardless of the difference in resources, scandals and other factors affecting popularity and quality. There are several positive feedback mechanisms keeping the rankings constant. These come from the multiple coordination games when choosing a university.
1) Smart and hardworking students want to be together with other smart and hard workers. If for some reason the best are in one location, then in the future all the best people have a motive to go to the same place. So the best arrive at that location and help attract other best people in the future. Similarly, party animals want to go to a university famous for its parties, and if many party animals come to a university, then it becomes famous for its parties.
Why would smart people want to be together with other intelligent folks? Just for interesting conversation, for useful contacts, collaboration. For these reasons, even the stupid may want to be together with the smart. Then an assortative matching results, as Gary Becker predicted for the marriage market (http://public.econ.duke.edu/~vjh3/e195S/readings/Becker_Assort_Mating.pdf).
2) Students want to go to a school with the best teaching staff, and the best professors want to teach the best students. I have yet to hear anyone wish for stupider students or teachers for themselves. Again the preference is the same among smarter and stupider students and professors, so assortative matching is a reasonable prediction.
3) The best professors want to be with other similar ones. Where there are such people, more will arrive.
4) Smarter graduates are likely to earn more and can donate more to the university. Then the university can hire better teaching staff, which in turn attracts better students, who donate more… The more talented also accumulate more power after graduating, in government institutions for example, which they can use (legally or not) to benefit their alma mater. Predicting this, again many people want to go there, and in the stiff competition the best get in.
5) If the employers believe that from some place, more intelligent people come than from elsewhere, then they are ready to make better offers to those coming from there. This makes the place attractive to all future employee candidates. Due to competition, the best get in, which justifies the belief of the employers.
6) Smarter people can be taught faster, at a pace that the stupider cannot keep. This mechanism gives everyone a motive to go to a school corresponding to their level.
7) Faster teaching means more knowledge during a standard length higher education, which the employers should value. The graduates of a school giving more knowledge are favoured, which makes the place attractive to everyone and leads to only the best getting in. The ability of the average student remains high, which enables faster teaching.