"Why is the sky blue?" and other commonly asked physics questions

There are some questions that we've all asked at some point or another.

In this article, I will give you the answer to 6 of these questions, in an 'easy to digest' manner. Here we go:

Why is the sky blue?

This is likely the most frequently asked science question of all time.

White light is actually made up of lots of other colours (specifically, the colours you see in a rainbow. More on that later).

The atmosphere is composed of many different molecules, and these molecules tend to scatter light.

However, some wavelengths (or colours) of light scatter more than others. In particular, blue light scatters much more than red light because it has a smaller wavelength. So, blue light approaches the atmosphere, gets scattered by the gas molecules and causes you to perceive the sky as blue.

Alright then, why is the sky orange and red at sunset?

The answer to this question is an extension of the last one. Orange/red wavelengths are longer and less likely to be scattered by molecules in our atmosphere. When we are at a certain 'line of view', aka. where we are when the sun is setting, these colours of light start to reach us.

And so, we see the sky to be orange and red at sunset (and sunrise).

How do rainbows form?

Like I said before, white light is composed of many different colours. As you may have seen before, as light enters a prism, these colours start to separate due to a process called refraction. Refraction occurs when light goes from one medium to another, changing its speed and therefore its direction. This is because in denser mediums, light has to travel around more particles to get out of the through, and so it takes longer (for example, light travels slower in glass than in air).

On top of that, certain wavelengths of light, or colours, travel slower than others (e.g. violet is slower than red), causing the colours to split up.

Water droplets act like a prism, splitting up the light into its many colours. With many different rain droplets, this causes the formation of a rainbow.

If you'd like a more in-depth explanation of this phenomenon, check out this video by 'It's OK To Be Smart".

How do clouds stay up?

Clouds first form in warmer areas (or at least cumulus clouds do). As you may know, warm air rises as cool air pushes it upwards. As this warm air rises, it begins to cool and starts to clump up into water droplets. With many of these water droplets, a cloud begins to form.

Once the wind begins to blow them away from the warm source, the clouds rely on condensation to stay in the air.

What I described earlier is known as condensation, and this condensation releases heat (it's actually the reason that you sweat).

As the cloud continues to have condensation occur on the inside of it, it's as if the cloud is warming up itself, which keeps it floating.

How much do clouds weigh?

To put it simply, a lot. The average cumulus cloud weighs 1.1 million pounds or about 407 asian elephants.

Why do stars twinkle?

Stellar scintillation, or the 'twinkling of stars', is caused by light from stars entering our atmosphere, and having some moved by turbulence (movement of the air). So, to someone on earth, the shifting or movement of light causes it to bend a bit, and make it appear as if it's twinkling.

References:

https://www.youtube.com/watch?v=DjByja9ejTQ

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

https://www.youtube.com/watch?v=5pYnC-ONdXQ

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question26.html

Picture from: http://www.sciencefocus.com/qa/what-makes-stars-twinkle

https://mgtvwnct.files.wordpress.com/2015/08/cumulus-cloud.jpg