Top 12 Tricky Science Questions Answered
Science is all about asking questions, and some of the most interesting and thought-provoking questions come from the imaginations of children. They can be staring out of a window and then drop such bombshells as:
"How much does the sky weigh?"
The media often laments how few parents are equipped to answer these questions. Fortunately, we live in the age of information, with answers just a few clicks away. The important thing is to never dismiss or dodge these questions. This inquisitive nature passes by all too quickly. If you are unsure of an answer, seek it out with your child! Children crave parental attention, and this is a great opportunity for you to spend time together while learning something new.
Here are some of the science questions I am asked quite often, particularly by my younger students. Each question and their related questions have simple answers and, where necessary, a link for more information. Enjoy!
12 Tricky Science Questions
- Why is the sky blue?
- Why does the moon appear in the daytime?
- How much does the sky weigh?
- How much does the Earth weigh?
- How do airplanes stay in the air?
- Why is water wet?
- What makes a rainbow?
- Why don't birds get electrocuted when they land on an electric wire?
- Do aliens exist?
- Where do birds go in the winter?
- Why is the ocean blue?
- Why is the sun the only star that can be seen during the daytime?
1. Why Is the Sky Blue?
The sky looks blue but really it is made up of all the colours of the rainbow. Each of these colours has a different wavelength. Some of these are smoother while others are choppy. Blue light waves travel in short, choppy waves. Like each of the other colours, blue light waves are scattered and reflected as they enter Earth's atmosphere and collide with gases and other particles. Because the colour blue has the shortest wavelength, it collides with nearly everything in its path and is scattered about the sky. This is why the sky appears blue.
Nitrogen, which makes up 78 percent of Earth's atmosphere, is the gas that blue light mostly collides and reflects off of as it makes its way toward Earth. If not for nitrogen and the short wavelength of the colour blue, the sky might be a different colour.
Is the Sky Blue Because of the Ocean?
No, the sky is blue because blue light waves have a short wavelength, causing this colour to get caught in the sky as it collides with gases and other particles.
What Is the True Colour of the Sky?
The sky has no true colour. While most of the time it is blue, sometimes it is not. It can often be pale blue, gray, or even white. The reason for this is pollution. Below is a table listing the different colours the sky the cause of its changed colour.
Colour of the Sky
Deep blue sky
This colour means the sky is very clean. This often occurs when a cold front brings clean air from the north, or when clean air from the ocean moves onto land.
Medium blue sky
This colour means there is lots of water vapor in the sky. It can also suggest the presence of sulfur from coal-burning operations. Lastly, it may be caused by the chemical emissions of plants and trees, such as those found in The Smokey Mountains of North Carolina and Tennessee.
Pale or milky-white sky
This colour indicates considerable air pollution from coal-burning power plants or chemical power plants. This condition often occurs in the summer when the air is still. There are also natural causes, such as volcanic activity or ocean plankton.
Gray or dark gray
Smoke from forest fires or agricultural burns can cause the sky to appear this colour.
Brown or brownish orange
Emissions from cars and trucks can cause a layer of this colour to form over the horizon. The main component of this kind of pollution is nitrogen dioxide.
Is the Sky Purple?
Simply by looking up, we can see that the sky is indeed blue and not purple. This is a frequently asked question, though, because according to the general answer to the question of the sky's colour (that because blue has a short wavelength it is caught and reflected in the sky), violet should be seen too, since its wavelength is even shorter than blue's.
It is true that violet is being scattered in the sky much like blue, but our eyes are not refined enough to see every colour of the spectrum. The sky is dominated by wavelengths between 400 nanometers (violet) and 450 nanometers (blue). When mixed together, our eyes are only able to see the dominant colour: blue.
Why Is the Sunset Red or Orange?
According to the science magazine Scientific American, the sunset is reddish because "when the sun is setting, the light that reaches you has had to go through lots more atmosphere than when the sun is overhead, hence the only colour light that is not scattered away is the long wavelength light, the red.
Further Reading: "Why Is the Sky Blue?"
2. Why Does the Moon Appear in the Daytime?
The moon does not produce its own light. We can only see the moon when light coming from the sun is reflected off of its surface. This means that whenever the moon reflects the sun's rays we can see it–even in the day time.
The visibility of the moon during the daytime also depends on its angle and its distance from Earth. When the moon and sun are on the same side of Earth, the moon is visible during the day; when the moon and sun are on opposite sides of the Earth, the moon is not visible during the day, as the Earth is blocking sunlight from reaching the moon's surface.
The reason we can see the moon and not stars during the day is because the sunlight reflected off of the the moon makes it 100,000 times brighter than the brightest star in the sky.
Can You See a Full Moon During the Day?
A full moon only happens when the sun shines on the face of the moon unobstructed by the Earth. Thus, you cannot see a full moon during the day. If there is daylight, at least part of the sun's light is shining upon the Earth, which would mean the entirety of the moon's face would not be illuminated.
What Is it Called When the Moon Is Out During the Day?
Currently, there is no scientific name for when the moon is out during the day. But, hey! There's nothing stopping you from creating your own.
How Long Is a Day on the Moon?
A day on the moon is equal to 29.5 Earth days. This means from sunrise to sunset on the moon, 29.5 Earth days would pass.
3. How Much Does the Sky Weigh?
The Earth has a surface area of 197 million square miles. Multiply that by four billion, and you have the Earth's surface area in square inches. With atmospheric pressure being an average 14.7 lbs (6.6kg) per square inch, the sky weighs roughly 5.2 million billion metric tons. Another way of looking at it, according to the United Kingdom's Science and Technology Facilities Council, is in its equivalent to Indian elephants. By that measure, the sky weighs equal 570,000,000,000,000 adult Indian elephants.
With all that weight, it's surprising we don't notice it as it presses on us evenly from all directions. That's because we've become used to it, and our bodies, having lived under the weight of the sky since infancy, have developed the necessary muscles to carry that weight. If we were to have grown up on another planet with less air, the weight of the air surrounding Earth might fatigue us. Luckily, that is not the case.
4. How Much Does the Earth Weigh?
The Earth weighs 5.972 x 10^24 kg, or around 6,000,000,000,000,000,000,000,000 kg. However, the Earth technically weighs nothing, because weight depends on the gravitational pull acting on an object and the Earth is floating in space. Still, mathematicians got the number above by looking at the strength of Earth's gravitational pull on nearby objects.
How Much Do All the People on Earth Weigh?
If the entire human population stepped on a scale, the weight would be 316 million tons (or 632 billion pounds), according to a study by the London School of Hygiene and Tropical Medicine.
Those who are overweight in the world carry a total of 16 million tons of extra weight, the equivalent of 242 million normal-weight people.
5. How Do Airplanes Stay in the Air?
Planes stay in the air because of the shape of their wings. Air moving over the wing gets forced downwards, which pushes the wing up. This push is stronger than gravity, and so makes the plane fly.
This is a very technical subject that the video below deals with very nicely. Planes take advantage of Newton's third law of physics, which states that for every action, there is an equal and opposite reaction. As air moving over the wing gets forced down, there is an equal and opposing force generated. This is a combination of the bottom of the wing getting pushed up, and the top of the wing getting pulled up.
Can an Airplane Stand Still in the Air?
An airplane cannot stand still in the air. This is a rule outlined by the laws of physics. Everything is always falling, but an aircraft can appear to stand still in the air by stabilizing its altitude. A helicopter, for example, appears to stand still in the air as its propeller pulls the aircraft up at the same rate gravity pulls it down. An airplane, too, can appear to stand still if there is a strong headwind coming towards it that keeps it in place.
Can an Airplane Go in Reverse?
Airplanes can in fact go in reverse. They a "thrust reverser" which changes the direction of the spinning blades in the thruster so that air is thrust forward instead of back. Airplane pilots usually only use this function for stopping once they land. When an airplane backs out of a gate at an airport, it relies on the use of tow cars to push it onto the runway. If the pilot were to engage the thrust reverser while parked in the gate, the amount of force coming from the thrusters would damage the airport as well as the people and vehicles on the ground.
Further Reading: "NASA: How Do Planes Fly?"
6. Why Is Water Wet?
"Wet" is ultimately just a word that applies to water. What we feel as wetness is actually coldness as the water evaporates. Below is an experiment from the Institute of Physics to test the feeling of "wetness" between two different liquids:
"The feeling of wetness is actually coldness. You can test this by comparing water with another liquid such as cooking oil, which doesn't evaporate so freely. Fill two small cups: one with water, and the other with cooking oil. (Young children should ask an adult to help.) Let both liquids come to room temperature for a day, or overnight. Dip one index finger in each liquid, lift them out, and then observe for a few minutes."
Liquids make surfaces wet (i.e. they stick to many solid surfaces) due to the electrostatic (opposite charges) forces between molecules. Water is polar—it has an uneven spread of electrical charge—which makes one end of the molecule positive and the other end negative. This causes water to be attracted to many surfaces and also explains many other properties of water.
Is There Dry Water?
Yes. Dry water is an unusual form of powdered liquid. It is a water-air emulsion in which liquid droplets the size of a grain of sand are surrounded by a silica coating. Dry water consists of 95 percent liquid, but the silica coating prevents the droplets from combining and becoming a bulk liquid. The result is a white powder that looks similar to table salt. It is also sometimes called "empty water."
7. What Makes a Rainbow?
White colour is actually a mix of several different colours. Each constituent colour of a rainbow is caused by a specific wavelength of light. When light hits a medium that forces it to slow down, the light ray bends, but not equally. Each wavelength bends by a certain amount, which causes the different coloured rays of light to exit the raindrop in slightly different directions. This results in the colours fanning out. When sunlight goes through droplets of water, the beam of light is split into the different colours that make up light. The same effect can be seen if you shine a light through a glass prism.
What Makes a Rainbow Curved?
A rainbow is curved because it reflects the round shape of the sun. Because you are on Earth, part of the sun is blocked, which why rainbows appear as a half or a quarter circle. If you were in an airplane and saw a rainbow below you, it would appear as a full circle.
Why Are There Only Seven Colours in a Rainbow?
There are only seven colours in a rainbow because only seven colours are included on the visible spectrum. While there are many more colours that are refracted when sunlight passes through a raindrop or glass prism, only seven can by seen by the human eye. These are:
The Colours of a Rainbow
- Red (outermost)
- Violet (innermost)
Can You See a Rainbow at Night?
Although rare, it is possible to see a rainbow at night. For this to happen, there must be rain, mist, or moisture in the air, and the moon must be reflecting the sun's light very brightly. When a rainbow occurs at night it is called a lunar rainbow or a "moonbow."
Further Reading: "Frequently asked questions about the rainbow."
8. Why Don't Birds Get Electrocuted When They Land on Electric Wires?
To be electrocuted you must be part of a complete circuit. This means you must touch both a positive wire, and a negative or neutral wire (or "ground"). If a bird was touching the ground while touching the wire, the ground would act as a neutral wire and the current would flow through the bird, electrocuting it. If the bird sat on a wire and touched the metal of the pylon or another wire, it would also complete a circuit and get electrocuted. Because the bird's only sits on one wire, it is safe.
The same would be true if a person were to jump onto and hang on a wire without touching anything else. As long as the current of electricity does not have a means of escape, you become incorporated into the wire and the electricity runs through you without causing any damage.
9. Do Aliens Exist?
The short answer is we don't know. We don't have any proof to state that aliens do exist, but we also don't have any proof to state that they do not. While we know there are planets orbiting stars at the right distance for liquid water to exist, we have no idea if there is any form of life beyond our planet.
Further Reading: SETI Institute
10. Where Do Birds Go in Winter?
In areas with colder climates, some common bird foods (such as insects, nectar, small animals, small reptiles) disappear for the season. The birds that rely on these foods fly south for the winter months, where they are more likely to find their favorite foods. Other birds, such as those that feed on subterranean insects or bugs that burrow within the bark of trees, stick around for the winter months, as their supply of food is constant.
How Do Birds Stay Alive in the Winter?
The birds that do not migrate in the winter utilize certain survival techniques to make it through the cold months. First, they grow extra feathers in the months leading up to winter so they can keep warm. Birds can also fluff up their feathers to make air pockets that keep them even warmer.
In the months before a spell of cold weather, birds also increase their fat intake. With more fat, they are able to generate more heat when they need it. Some birds even feather flock together, which is when they pack together in a tight huddle and share body heat.
And, of course, when the sun is out, birds sunbathe to keep warm. Even the coldest winters have a few sunny days.
11. Why Is the Ocean Blue?
The ocean is not blue because the sky is blue, but it is blue for the same reason the sky is blue: The ocean is blue because the wavelength of blue light is easily captured, whereas the wavelengths of colours like red and orange are absorbed by the water and allowed to pass through it. In the words of the science magazine Scientific American:
"The ocean looks blue because red, orange and yellow (long wavelength light) are absorbed more strongly by water than is blue (short wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue."
12. Why Is the Sun the Only Star That Can Be Seen During the Day?
Stars glow during the day, but they are impossible to see because of the brightness and closeness of the sun. Also, the light coming from the sun is scattered into the bright blue colour that we are familiar with as being the colour of the sky. This blue-tinted atmosphere plays a part in blocking out the stars, which in fact shine very faintly.
On the other hand, if you lived on the moon, its lack of atmosphere would allow you to see the stars both day and night.
The Hardest Question?
Which Question do you think is most difficult to answer?
Sources for Finding Answers
- BBC - BBC One Programmes - Bang Goes the Theory
Bang is the BBC's guide to popular science. Watch videos and do real experiments at home.
- The Big Question
A Blog set up after the 2008 UK National Science and Engineering Week. Some great headscratchers answered here, including the all-time favourite: Which came first? The Chicken or the Egg
Questions & Answers
© 2012 Rhys Baker