Ask a Scientist

Physics questions

• Is there a specific time of year when NZ is more vulnerable to lightning strikes?
• Why are different sorts of clouds different colours, from white to very dark grey?
• How can a brown cow, who eats only green grass, produce only white milk?
• How does the physics demonstration work whereby a test tube can be made invisible when immersed in a liquid?
• What stops an electron, say in hydrogen atom, from being drawn into the nucleus since it is attracted by the proton charge? (Is it only speed momentum like planets' centrifugal forces, and the centre of the nucleus is so small that it misses the target and spins around the nucleus? or is it something else?)
• Can water in a gravity-fed irrigation scheme be made to also go briefly uphill using a reverse syphon?
• When the windows in the car are down and I'm driving at a higher speed (say 60 kmph or more) a pulsating sound is created that really hurts my ears. When I put the windows up or when I slow way down, the sound goes away. Why is that?
• Why can they not get the volume even for TV programmes and commercials?
• What design features are important in a rugby ball? Does spinning a rugby ball when it is thrown affect its performance?
• I collected some black sand from the beach and did some experiments with it, with bags and magnets. I noticed it was magnetic. Why doesn't magnetic sand rust?
• What actually defines the arc of a rainbow? Is it the time of day, position of the sun, season? There appears to be many different degrees of curvature, some appear high with a small radius, others low and flat etc. Regardless, no matter how hard I look, I'm still chasing that "pot of gold"
• Is it necessary for a rocket, while in space, to be jet-propelled?
• How and why does space weather affect the power grids, satellites, and electronic equipment?
• Do the various scientific bases in the Antarctic have freezers to store their food? i.e. do they actually need them?
• When finishing pouring wine, red drips more than white. Why is this?
• When I was young, at movies watching westerns, the spokes on wagon-wheels sometimes turned slow, stopped or went backwards. This was the stroboscope effect caused by film frames being presented to our eye in rapid succession.
• How do scientists know it is time to add a second to clocks?
• If you shake the loose water off your hands before drying them under a hand-dryer in a public toilet, will this make a significant difference to the time taken to dry your hands? How much electricity would this save? Could it be extrapolated to an estimate for how much electricity would be saved if everyone in NZ did the same and whether we should have a national campaign to shake hands before drying?
• I read recently that the Large Hadron Collider could possibly have created a microscopic black hole. In theory that tiny black hole would simply swallow anything in proximity to rapidly becoming a large one, meaning the end of Earth. Is this so?
• Why do mats move when placed on carpets ?
• I photographed a triple rainbow. Is it rare or just unusual for this to happen and what causes this?
• How does this Sun effect happen? It lasted only 2 minutes.
• Yesterday I fell straight forward on a sidewalk after tripping. I caught myself with both hands near the wrist, then immediately rolled onto the grass. I wasn't hurt. I've been puzzling over the fact that I immediately rolled over after falling on my hands. It seemed an automatic reaction. Does it have something to do with the energy of falling?
• Why do rockets need to go so fast to get into outer space? Jumbo jets lift off with an almost agonising slowness, so why can’t rockets do the same thing and just keep going up at a similar gentle pace until they reach orbit?
• My wristwatch had a luminous dial but with time it faded so much as to be unreadable. However when I was in the bush one night I had cause to shine my flashlight on the dial, and when I returned to the tent my watch dial was luminous again. It did not last for long though. What caused it to be re-charged?
• My wristwatch had a luminous dial but with time it faded so much as to be unreadable. However when I was in the bush one night I had cause to shine my flashlight on the dial, and when I returned to the tent my watch dial was luminous again. It did not last for long though. What caused it to be re-charged?
• When ordering a beer in craft beer and other pubs, I usually ask for a pint. The glasses I am given vary dramatically in size. Is there a standard?
• Recently there has been news that a solar flare crossed the orbit of the Earth in recent times, missing the Earth by just 5 days. I understand that should a flare such as this strike the Earth, electricity supply, electronic appliances, and communications would be in jeopardy. What would be the most likely consequence of such an event and what could happen in a ‘worst case’ scenario?
• Richard Mitchell, of Paraparaumu Beach, asked:-
• Why do flies appear to suffer no damage when they bash into window panes?
• Many years ago I saw a rainbow with another upside-down sitting on top of it. I have never heard of anyone else reporting this. How could it happen?
• A newspaper featured a photograph of a rainbow. I have what looks like the exact same photo, which I took on the same afternoon but 200 kms to the East. Can this be the same rainbow? If so how far can they been seen.
• A colour wheel consists of a series of black lines which, when spun, produces colours. Why is this so?
• Is it true that the plastic foam which provides the cushioning in safety helmets degrades over time and becomes ineffective ?
• My dad could not go to work because a cow derailed the train he was going on. How can a 270kg cow derail a train?
• Why do our electric clocks seem to gain about 10 - 15 minutes over a 10 day period whereas the clocks on the microwave and the electric range keep perfect time over the same period.
• What causes the colour in clouds, from white to grey to blue-black? Steam in the kitchen is transparent but would it become coloured if in great depth, similar to water? Bath water is colourless but the ocean is green or blue. In both cases are other ingredients involved?
• I was watching USA golf and the commentator said that US golfers aren't used to playing in rain as there is a huge chance of lightning when it rains in the USA. The same seems to happen in Australia and parts of Europe. In NZ we have lots of rain and few lightning storms. So I was wondering if the reason has something to do with islands and continents as it seems to me the bigger the land mass the more lightning?
• Recent light shows have had strings of large white translucent globes gently change colour through six colour ranges. How is this done?
• How does a DVD keep on the track on the disc? It isn't like an old record where the needle follows a grove?
• During the winter I have had condensation under the toilet cistern and puddles of water on the toilet floor. Is this due to a recently installed heat pump and, if so, why is the dampness occuring now?
• If hydrogen is used to run a car, could the resulting water be re-electrolysed to produce a continuous hydrogen cycle, and do the same gasses bubble up from both electrodes?
• I read somewhere that enough solar energy falls on Australia in a day to provide the world's energy needs for a year. Is this correct?
• Will a leather pouch for a cellphone prevent the possible human tissue damage caused by the radiation emitted by cellphones? If not, what can?
• Why are clouds white?
• Is natural radiation dangerous?
• What is radioactivity and how is it made?
• Can the gamma rays from a smoke alarm build up on the casing and cause it to be radioactive?
• Scientists are trying to make heavy atoms possessing 'magic' numbers of protons and neutrons (such as 126), which should be extra stable. What is the reason for the instability of the light atoms Technetium and Promethium, which have no stable isotopes? Are 43 and 61 'anti-magic' numbers?
• Why are scientists making artificial/new atoms? Of what use are they?
• Why does the Moon look red sometimes? What does it mean?
• Why does the Moon look red sometimes? What does it mean?
• As a motorist traveling regularly up and down between Dunedin and Christchurch, I have often pondered the question of how long a rest stop one would need to avoid ever catching up again with the oversize traffic ahead. For example, I recently became stuck behind a line of sheep truck, milk tanker, private car and a truck and trailer unit. The convoy speed was 80 to 100kph. The vehicles were too close together to pass individually. Fortunately, they all passed the Waimate turn-off cafe, so I stopped for a coffee. Sure enough, I didn't catch up with them again. Assuming that all were traveling to the same destination, is there an underlying rule of thumb about the time I need to stop for to ensure I don't get held up again?
• If the eye is a single lens shouldn't the image be up-side down on the retina?
• Ever since I was a child, I have been led to believe that 'wild-fire' that occurs on windy nights was different from lightning.What is wild-fire?
• I read that Cherenkov radiation occurs when a charged particle moves faster than the speed of light through a transparent medium. But I thought nothing travelled faster than the speed of light?"
• When crossing a causeway in the harbour the tidal flow direction is quite clear as water rushes through the constriction. How is tidal flow direction determined where there is no constriction?
• The harbour surface often shows wrinkled lines of water moving at right angles to each other. How can these ripples criss-cross without losing shape?
• Why can a blowfly fly full speed into a glass window without appearing to suffer any ill-effects?
• Why does food heated in a microwave oven cool quicker than that heated in a pot on the stove, even though both appear to be boiling?
• Why is light faster than sound?
• How many different types of light are there?
• How do solar panels work?
• Why does light make heat?
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• Why cannot light escape a black hole?
• Why is it that no matter what colour bubble bath is used the bubbles are always white.
• I have two air-temperature thermometers, one about 110 years old and a new cheap one, both made by the same manufacturer and both containing a red fluid. They register about 3 degrees Celsius different. Why? And how can I find out which one is accurate?
• How do steam train whistles get that woo-woo sound?
• What is in the bubbles in iceblocks?
• Why is ice sometimes clear and sometimes cloudy?
• When driving into a ground floor car park the AM radio stations go noisy and vanish but the FM radio stations can still be heard. Why is this?
• If a driver was faced with a car of similar speed (100km/hr) coming straight at the driver on the wrong side of the road, and the drivers only options were to hit the car or a solid concrete bridge abutment, which should the driver choose?
• How does a thermos flask keep my Dad's tea hot or his fruit juice cold?
• When making a single cup of tea is it more efficient to use my electric jug (1400W) or my microwave oven (600W)?
• If an electrical current increases, do more charges leave the battery or do they just travel faster?
• Why does the handle of a cup not get hot when the cup is?
• How does heat travel?
• Why does heat travel?
• Why do mountains appear to be blue when seen in the distance?
• If I place two bar magnets with like poles facing they repel. However, if I place a 2cm wide bar of unmagnestised steel (a keeper) between them then both are attracted to the keeper, ie the attractive force to the keeper is greater than the repulsive force between the opposite poles. Why is this?
• My mother and grandmother often mention that following washing, white clothes always take longer to dry than non-whites. Are they correct?
• Is it true that water can be electrolysed by a car battery into hydrogen and oxygen to be used as a fuel supplement to petrol?
• During a recent drive we came to a railway crossing. The barrier arms were down but no train was coming. I would like to know what makes the barrier arms go down when there is no train coming.
• I am informed that the human body acts as an aerial, and picks up any wavelength that matches a person's height. Is this so?
• Why is the moon yellow at night but white during the day?
• At the gym my excercycle has a mesh cage over the fan on the wheel which cools the rider. In cooler weather I put my towel over the cage to stop the draught. It is a lot less effort when the cage is covered by the towel. Why is this?
• When a marble is rolled over a flat surface why does it make a noise?
• Why does my long hair stick up after I have brushed it?
• How can glass be broken by sound?
• What causes gravity?
• When we look in a rear-view mirror the number plate of the car behind appears back to front but not upside down. Why is this?
• Why does water take away friction?
• In order to show students that radio waves wont travel through a metal mesh I wrapped a walkie-talkie in mesh, but it picked up a signal. I then tried wrapping it in two layers of aluminium foil, but it still received a signal. Why was this?
• How can we keep a swing going without touching the ground or being pushed?
• Why does water make bubbles when it boils?
• Why do we see a reflection off the clear windscreen of a car?
• How do scientists measure the speed of light?
• Why am I more buoyant when floating in sea water at Tonga than around New Zealand?
• How does a magnet pick things up?
• How does a magnetic field go through things?
• What are permanent magnets made of?
• How do you make an electromagnet?
• Why do some balls bounce?
• Why is lead not transparent but lead crystal glass is?
• What goes up but never comes down?
• Are bubbles liquids, solids or a gas?
• When a balloon pops why does it make such a loud bang?
• When a ballon pops why does it make such a loud bang?"
• How does a garden solar-powered light work?
• Why does light slow down in glass and what is the fundamental cause of the colour display in prisms and diamonds?
• Why is it that when a half-full bottle is spun in a vertical circle the liquid doesn't fall out when the bottle is upside down?
• We often see sea fog form over the sea, then drift up the river before spreading over the land. Why is this?
• How does humidity work? How can there be more moisture in the air in summer than in winter when it is wetter weather?
• According to Einstein the speed of light is constant for all observers irrespective of their speed and location. Thus whether or not an object is said to be rotating will depend upon the observer. However, rotating objects distort. Our Earth is slightly flattened at the poles for this reason. Does this not imply that the rotation is intrinsic to the object itself and is not related to the measurements of independent observers?
• Why does the speed of sound in air increase with temperature?
• What causes gravity?
• What is the colour black?
• Think of a headlight on a car travelling at 100kph. If light is incapable of travelling faster than the speed of light (c), ie at c plus 100kph, would then the light be brighter immediately in front of the filament? Could it be compressed in someway? If not why not?
• Bernoulli's Theorem predicts that air flowing around objects will exert the lowest static pressure where the air flow velocity is highest, and the highest static pressure where the velocity is least. What common examples demonstrate these forces?
• Bernoulli's Theorem is the usual explanation for how aircraft wings generate lift, in that an aerofoil causes the air to travel faster over the top of the wing. It seems very odd that a fluid moving at a faster rate is at a lower pressure. One would think that with faster speed there would be more energy involved and there would also be an increase of pressure in the fluid. Why not?
• I learned in physics that electricity stays on the outer surface of a metallic shell. Does that mean when a Medieval knight in armour is hit by lightning he would be OK?
• If nothing can travel faster than the speed of light, and supposedly strange things happen if anything exceeds the speed of light, how can light travel faster than the speed of light if, for example, you throw a torch that was switched on?
• While flying a helicopter my Dad saw a rainbow which was a complete circle. Are all rainbows complete circles?
• Why is water invisible?
• If we drilled a hole right through the Earth and dropped a two-tonne lead weight would it go right through or stop at the middle?
• Why do bubbles in fizzy drink, or boiling water, stream from a small number of places?
• How does induction heating on a stove work?
• Polaroid sunglasses polarise light so that when when looking through two sunglasses at right angles to each other no light gets through. However when a third sunglass lens is added between them light can get through. Why?
• During a heavy frost, ice made a very attractive pattern on the glass roof of our conservatory. Why did this pattern form?
• How did Rutherford go about splitting the atom?
• Surface tension draws water up a tube. Could a very large number of very fine tubes be used to draw water to the top of a water tower and use this water to generate power?
• I saw a demonstration in which a lightbulb placed in a microwave oven glowed. Why did it?
• Why is it bumpy flying through clouds?
• Is it possible to see a rainbow as a complete circle?
• Why is speed at sea measured in knots and what are they?
• In the film "The Bourne Identity" the hero, in a tight spot in a stairwell, grabbed the body of a dead baddy, jumped over the bannister and fell several stories, using the baddy's body to break his fall. Would this be possible?
• What is the people-carrying vehicle which has the most kinetic energy?
• Why do some desert people wear dark coloured clothes? Isn't it cooler to wear white?
• How is lightning formed?
• Why does sound travel faster in solids than in air, whereas light travels slower?
• Why is it necessary to compress hydrogen gas to run a car of the future?
• Why do I get an electrical shock when I touch the car door to get out?
• How does water conduct electricity?
• How does electricity go through power lines?
• How does water turn into electricity?
• During the second world war powerful sleeve valve engines were developed for British fighter aircraft. Why hasn't the motor vehicle industry used these engines in production cars?
• What happens to the electrons when an alpha particle is ejected from a radioactive nucleus?
• Does burning coal help produce the ozone hole over New Zealand and will the hole repair itself?
• Bill Holvey, of Kirwee, asked:-
• Why do modern fridges "hum" more than old ones?
• Elizabeth Andrews, of Christchurch, asked:-
• Is there a container that wont expand at all under pressure inside it?
• Why do you go into space in a rocket and not in a plane?
• If the ozone hole gets too big will people start to die?
• How long does it take a raindrop to reach the ground?
• How can you measure the size of raindrops?
• How big is a raindrop?
• How come a video camera sees the invisible signals from a video remote unit?
• How does a TV remote work?
• Where does wind come from?
• Where do the bubbles come from in the bottom of a glass of fizz or beer?
• Why does the North-West Arch occur?
• Where and when is it best to look for aurora?
• What causes the Northern/Southern Lights?
• Why is water so blue in the deep bits?
• Why are planes made from metal?
• Why is it that when I look into my dinner spoon my reflection is smaller than me?
• Morgan Allington, of Balclutha Primary School, asked:-
• How do mirror's work?
• What is lightning made of?
• How do magnets work?
• How did Sir Earnest Rutherford split the atom?
• Why does electricity go through metals?
• What was the first computer like?
• Why do magnets stick on the fridge?
• What is gravity? How does it work and where does it come from?
• Is there a difference between heat and infrared? How is it we can feel an electric heater but not the infrared TV changer?
• When sucking helium into your mouth, why does your voice go squeaky when talking?
• Is radiation still present in food for several minutes after the food has been cooked in a microwave oven?
• How did Einstein come up with E = Mc^2
• Does the moon have any gravitational pull on the earth?
• How fast do raindrops fall?
• How does an aqualung work?
• What will happen to the computers that are not compatible for the year 2000?
• Why is glass clear when the sand it is made from is opaque?
• Why is it that toilets flush and plug holes drain in different directions in different hemispheres?
• How can we reduce the amount of noise in our school hall?
• What is the physics involved when doing an ''ollie'' on a skateboard?
• Why does sound travel faster in solids than in air?
• Plane wings are curved at the top and flat at the bottom and are probably only made to work the right way up. So how can planes fly upside-down?
• How are ball bearings made?
• Why does the computer screen appear to flicker when filmed on video or TV?
• Why can birds stand on power lines but humans get electrocuted?
• Nuclear fission reactions produce nuclear waste but nuclear fusion reactions dont. Is it possible to do a nuclear fusion reaction with the waste products of a fission reaction and thus eliminate nuclear waste?
• How does electricity heat up the water from our tap?
• How fast does electricity travel through a wire?
• What do you wear when you fix power lines?
• How come when you touch a light bulb it is hot?
• Have scientists succeeded in producing power from nuclear fusion?
• How come the ozone hole occurs over the Antarctic and New Zealand, two of the least polluted places on Earth?
• A magazine reports that hot water freezes quicker than cold water. I tried this in our freezer but there was no difference. Is it true?
• How much electricity gets wasted every day?
• Is it realistic that cars will eventually be replaced with solar-powered cars?
• How big or small can rainbows get?
• Why is a rainbow bow-shaped and does it go round in a complete circle?
• Kate Johnston, of Ardgowan School, asked:-
• Is time travel possible?
• Can nuclear power be used to drive a space ship?
• What colour is an atom?
• How many phone calls can a telephone line transport at the same time?
• Why do I see an array of lights when looking at a distant yellow street lamp through material used in cotton sheets?
• Is a screwdriver a machine?
• Is a screwdriver a machine or not?
• How do butterflies and moths get colours on their wings?
• How are mirrors made?
• The pupils of Room 9, at Addington Primary School, asked:-
• Why does heat travel along metal faster than glass?
• Why does a reflection in a mirror reflect left to right and not up to down?
• Has anybody seen an atom?
• What are atoms made of?
• When things become cold the particles slow down. Is this why materials become brittle when cold?
• If black and white aren't colours what are they?
• How can there be a reflection from water when it is clear?
• How do glasses work?
• How does Newton's cradle work?
• Why is ultraviolet light so damaging?
• Why is water wet?
• If we stopped using toxic gases and chemicals today, how long would it take the ozone layer to recover to normal?
• Can cars run on water?
• How and when were magnets first mass produced?
• How did the ancient Egyptians lift the enormous blocks to make the pyramids?
• We have been talking about Concorde and would like to know if a plane can keep flying upwards into space?
• Where does electricity go when you have finished with it?
• How many different types of thermometer are there and when were they first used?
• How are mercury thermometers made and how do we check them?
• How do sound tape machines work?
• Jessie Gibb, of Ardgowan School, asked:-
• Why can you see dots when sitting close to a TV screen?
• Why doesn't air go out into space so we can breath on the moon?
• How does television work?
• Why do bathroom scales indicate a lower weight when used on carpet than when used on a hard floor?
• Can motorbikes be made to run on fuels other than petrol?
• Do the upper layers of the atmosphere spin at the same rate as the earth or do they stay still?
• Why is water clear?
• Is it possible to have a world in which everything is opposite that on Earth?
• What makes the dayglow yellow paint on my cycle helmet stand out at a distance?
• What is chaos theory?
• Evan Blanch, of Alexandra, asked:-
• Sarah Smith, of Ardgowan School, asked:- Melissa Robertson, of Kingswell High School, asked:-
• Why did my fizzy drink foam up when I added ice cream to it?
• Why do some beaches have bigger waves than others?
• If a torch was shone around a closed ring of mirrors, what would happen when the torch was turned off?
• Do sounds echo in space?
• Why is window glass clear?
• What causes echos?
• Does the red laser light used in decoders at supermarket checkouts emit radiation that causes sterility?
• Why does infrared radiation get absorbed by carbon dioxide gas?
• How do you prevent frost damaging houses?
• Why is fire red? John Campbell, a physicist who is a consultant firewalker, responded.
• Hillary Riddle, of Mokoia Intermediate School, asked:- Giles Reid, of Ilam Primary School, asked:-
• What is plutonium and why did spacecraft, such as Cassini which was sent to Saturn, need it?
• Why, when you telephone someone overseas, is it sometimes a good line and sometimes a bad line?
• Why do we have sun-showers?
• Why does a straight stick seem bent when part of it is pushed into a swimming pool?
• Can the information on a credit card be destroyed if the magnetic strips of two cards rub together?
• Recently I saw a rainbow at night. Are these common?
• Why does light travel so fast?
• How do nuclear weapons work?
• When water is boiled, where do the bubbles come from?
• Why is the sun so hot?
• Is there anything colder than liquid air?
• How are rainbows formed?
• How does a radioactive smoke detector work?
• How do rainbows get their shape and why are they all the same?
• Why are planes all the same shape?
• Why do clouds float?
• Why is black sand hotter than white sand?
• What is the difference between forked lightning and sheet lightning?
• Why does thunder roll?
• Is there anything colder than liquid air?
• Why does the sky change colour when the sun sets?
• Ryan McIntosh, of King's High School, asked:- Paul Manson, of Nayland College, asked:- Emma Malone, of Christ the King School, asked:- Room 6, of Balclutha Primary School, asked:- Emma Hendriks, of Sawyers Bay, asked:- The year 10 class at Marlborough Girls' College asked:-
• Is there anything smaller than an atom?
• Sophie Goodwin, of Mokoia Intermediate School, asked:-
• Do the bends in the tube forming a trumpet have any effect on the trumpet's sound?
• What is the function of the bell shaped end of a musical instrument such as a trombone?