Tricky Questions for Parents

In a January 2012 nationwide UK survey of 2,000 parents by The Big Bang UK Young Scientists & Engineers Fair (broken link), almost one in three parents (30%) say they take a grilling from their curious kids on a daily basis, and it's leaving about a quarter (24%) of mums and dads frustrated and embarrassed because they find many questions difficult to answer.

The 10 most common questions that parents struggled to answer:

1. Why is the moon sometimes out in the day?
2. Why is the sky blue?
3. Will we ever discover aliens?
4. How much does Earth weigh?
5. How do aeroplanes stay in the air?
6. Why is water wet?
7. How do I do long division?
8. Where to birds / bees go in winter?
9. What makes a rainbow?
10. Why are there different time zones on Earth?

How many can you confidently answer yourself? Answers are below.

Other results from the survey:

• Science and maths top the subjects their children enjoy the most and yet these are the subjects that fill more than half (52%) of parents with fear.

• While a third of parents (31%) would actively research answers to clever questions, many are using sneakier tactics to save face when flummoxed by their child’s musings. A fifth (21%) make up answers or pretend nobody knows and one in six (16%) put the burden on their partner.

• More than a quarter (26%) of parents think their children know more about maths and science than they do.

• One in five (20%) wish they had taken more of an interest in maths and science at school.

• 10% of mums say their limited knowledge is down to the lack of support and encouragement girls received in maths and science when they were at school.

• One in six (16%) believe their children’s curiosity for science and maths is heavily fuelled by educational TV programmes, such as Frozen Planet (35%) and Wonders of the Universe (20%).

Questions and Answers

1. Why is the moon sometimes out in the day?

   • The Moon orbits Earth about once a month but Earth orbits the Sun once a year, which means the Moon is not always in the same place in the sky relative to the Sun. Compared to the Sun it seems to move "backward" across the sky from night to night (or day to day), getting further away from the Sun for a couple of weeks then closing in on the Sun again for a couple of weeks, approaching it from the other side. This means the Moon can be seen at any time of the day at some point during the month.

   • It also means that if the Moon is east of the Sun we know that it's waxing (getting bigger), or if it's west of the Sun it's waning (getting smaller), because it's getting further away from the Sun in the sky, or nearer to it, respectively.

   • If the Moon is directly opposite the Sun in the sky the whole side of the Moon facing us is lit up, so we see a full Moon; it has finished waxing and is about to start waning. At this time the Moon will only be visible at night. If the Moon is in the same direction in the sky the far side of the Moon is lit up, so we cannot see it; it has finished waning and is about to start waxing. At this time the Moon will not be visible during the daya or night.

2. Why is the sky blue?

   • It's basically because of scattering of light, as light gets bounced off particles in our atmosphere. Blue light has a shorter wavelength than red light so is scattered more easily, so the sky ends up looking blue. Near the horizon there's more atmosphere to scatter light because we're looking through the air at an angle. This has the effect of scattering some longer wavelengths such as red light as well. When all colours of light are mixed together white light is the result, and so the sky near the horizon is a whiter blue than the zenith (straight up).

   • The easy scattering of blue light is why fog lights on cars are often yellow, and why blue tinted headlights are a really stupid idea.

   • Sunsets are also red because of scattering. The light from the sun passes through a lot of atmosphere which scatters the blue light out of the light directly reaching us.

   • Demonstration: Add a few drops of milk to a large jar of water. Shining a light on it from above will give it a slight blue tint, while shining the light from behind will give it a slight red tint.

   • The real question should be why isn't the sky violet? Violet light has a shorter wavelength so is scattered even more easily than blue light, but our eyes are much more sensitive to blue light than violet light so we don't notice any violet tint. Also, oxygen gas has a very slightly blue colour, so any light coming to us from the atmosphere will be slightly coloured by this. This is more noticeable in photos of Earth taken from space. (Liquid and solid oxygen is clear with a pale sky-blue colour.)

3. Will we ever discover aliens?

   • Cynical answer: Prophecy is always very difficult, especially with respect to the future.

   • Christian answer: Probably never. There's no indication in the Bible that there is any other intelligent life in the universe and there would be complex theological questions raised if we did (which would probably be fun to try to sort out).

   • Secular answer: There are so many planets around so many stars in so many galaxies that there "must" be a huge number of aliens, so either they're actively avoiding us, or they're hiding from us, or they have already been discovered and our governments are lying to us.

     It's important to note that this answer completely depends on the assumption that life spontaneously arises from non-life as a matter of course. However, all science experiments on the topic clearly show that life only ever comes from life. Indeed, we actually have no idea how life even could arise from non-life, or how it coud evolve to higher forms of life without going extinct due to a build-up of harmful genetic mutations – a serious problem even over tens of thousands of years, let alone millions or billions of years.

4. How much does Earth weigh?

   • Nothing. Earth is in free fall around the Sun so it has no weight.

   • Earth's mass is about 6×10²⁴ kg. (That's a 6 followed by 24 zeros.)

   • Weight and mass are different things. An object's mass doesn't change but its weight depends on the gravity it is experiencing. The Moon has ¹/₆ the surface gravity of Earth, so a child who is 30 kg on Earth would weigh only 5 kg on the Moon (although the kilogram is actually a unit of mass). Objects in free fall experience no weight.

5. How do airplanes stay in the air?

   • A mix of Bernoulli's principle from the aerofoil shape of the wing and down thrust from the angle of the wings.

   • The aerofoil shape of the wing means the air moving over the top of the wing is moving faster than the slower air underneath the wing. Bernoulli's principle says fast moving air has a lower pressure. With higher pressure underneath the wing than above it, lift is generated.

   • Demonstration 1: Bernoulli's principle can be seen by holding the near edge of a sheet of paper horizontally just under your mouth, with the rest of the paper hanging freely away from you. Blow onto/across the top of the sheet of paper and the trailing edge will rise.

   • Demonstration 2: Find a vacuum cleaner with a "blow" mode (or a hair dryer set on cool). Take off the vacuum cleaner's head so it just has a round nozzle, then point it upwards and set it going. A table tennis ball can be suspended in the stream of air, with the Bernoulli principle keeping the ball centred in the jet of air. Sometimes this can be so effective it will even work if the air jet is pointed sideways or upside down.

   • Down thrust is created simply by moving air bouncing off the lower surface of the wings. It's the same reason simple kites fly. The down thrust is why planes can fly upside down, when Bernoulli's principle is acting the wrong way.

   • Demonstration: Generate down thrust by blowing hard on the underside of a piece of paper.

6. Why is water wet?

   • Wetness is a property of water with most substances – the water sticks to the substance. There are some substances such as oil that water doesn't wet, and there are some liquids such as mercury that are notably non-wetting – it sticks so much more strongly to itself than to other non-metallic substances that it doesn't wet the other substance. Soap or detergent can be added to water to reduce its surface tension and increase its wetting ability.

   • Related to the wetting ability of water is the cooling effect water has as it evaporates. This cooling effect makes the water more noticeable, and seem even wetter, because it makes the water cooler than the temperature it started at. The cooling is caused by the fastest moving water molecules being the ones that escape by evaporating, leaving behind the slower moving molecules – the water that's left is cooler. Evaporative cooling can be quite significant on a windy day, which is why staying in a cold swimming pool can be much more comfortable than standing wet beside the pool in the wind.

   • "The wetness of water is thought to be due to its high moisture content." – (Dr) Jason A. Rush, Dept of Mathematics, Edinburgh University. (This is one of the more interesting answers given here.)

7. How do I do long division?

   • Cynical answer: Sounds like you don't. You need some maths tutoring!

   • Avoidance answer: The first step is knowing your times tables. This is really useful, and not just for long division – times tables form a foundation for doing all sorts of more complicated maths. Ask me again when you're under two and a half minutes with those things.
      

8. Where do birds/bees go in winter?

   • The "Let's Explore" answer: "Western Springs. Shall we go take a look?"

   • Cynical answer: Still using those American textbooks, huh? No, they don't fly south for the winter. We live in temperate New Zealand, and anyway there's only Antarctica south of us.

   • More complete answer: It depends on the kind of bird. If they're seagulls they probably hang out at the local park, especially when a storm hits. If they're pigeons, Albert Park is a likely spot to find them. Some birds go on holiday to somewhere warmer and with more food (these migrations can be thousands of kilometres), while bees just sit inside their hives eating honey and keeping warm.

9. What makes a rainbow?

   • Little drops of water in the air act like tiny prisms, splitting the white light up into its spectrum – a rainbow. See the notes on rainbows in the Physics section. The splitting of white light into colours occurs because different colours are bent, or refracted, different amounts when they pass from one optical medium to another (like air to water and water to air).

10. Why are there different time zones on Earth?

    • As Earth spins, the Sun only lights one side of it at a time. When the Sun is in the middle of the sky for the people on one side of the planet it's the middle of the night for the people on the other side. It would be way too confusing if everywhere on the planet had to use the same time. For example, you'd go traveling and find people were having dinner at what you thought was 8am and going to bed at noon. (This is a good question to get children thinking about the consequences of time zones or not having time zones.)

    • China used to have 5 time zones but in 1949 was changed to a single time zone.

    • Demonstration: Use a ball or orange and a table lamp in a dark room; one side is brightly lit, the other is dark.