Answers to last issue's Do You Know?

1. I have to create passwords for using the Internet but am worried if they are safe. What makes a good password?
Ans: With the amount of personal information people put online, keeping our data protected is clearly important. A good password is one that is difficult for other people to guess and at the same time easy for you to remember. It should be tough both for people you know as well as for malicious attackers who might make billions of guesses (using computer programs) to figure out your password. 
Unfortunately, some of the most common passwords used by people include: 'letmein', '12345', and the very original ‘password’!
To create a good password, pick a word or phrase that you can remember but don’t use phrases from film songs or anything else that’s popular and don’t use the name of your friends, family or pets, or someone's phone number, or other information people might know about you.
You might use the first letter of each word in a phrase that you make up then add some extra symbols and numbers or capital letters in the middle. Don’t just put them at the beginning or end and don’t substitute numbers that look like letters. It’s good to have at least 12 characters in total. 
But then that’s a lot to remember. Can we save time by making one "super password" and then use it for every account?
Unfortunately this is not good, because if it is stolen, you lose all access. It is much better to use different passwords for every account and to write your passwords down in a secure place.

2. I know that water is made up of hydrogen and oxygen. At what temperature will water split into hydrogen and oxygen?
Ans: There is this closely related question of how much energy is needed to split water into hydrogen and oxygen. You can do it electrically with about 1.3 volts of electricity. However, to do it thermally, we have got to heat it up to over 2,000 degrees Centigrade. The hotter you get, the more complete the dissociation - you split the molecules up.
It is actually a suggested way of making hydrogen - you heat up water at very high temperatures. You then have to somehow separate out the hydrogen and oxygen because otherwise, it’s easily hot enough to burn and condense back to water again. So you need some kind of membrane to separate the two which exists - it is a special kind of ceramic, and you can separate the two and get hydrogen out. Thus yes, we can split water somewhere about 2,000 degrees C.
In general, catalysts help reactions happen at different temperatures. So can we find the right catalyst so that it need not be so hot as 2,000 degrees?
Catalysts certainly help with electrolysis. But apparently, the energy needed to split apart water molecules thermally is too much for catalysts to be of help.

3. When I apply a force on an object, how quickly can the force propagate? Can it propagate at the speed of light?
Ans: Let us ask the question this way. If you had a really long tube and filled it with rigid balls and then put another one in the end, would a ball come out at the other end instantly or would there be a delay at least as much as dictated by the speed of light? We have a tube full of balls and we are going to apply force to the ball at one end and we want to see how quickly the force can propagate through the assemblage of balls.
Now the force we apply is going to compress one of the balls slightly elastically and that is going to then exert a force on the next ball on the tube which will compress that force on the next ball on the tube. That compression can only propagate with some delay: at best it can propagate at the speed of light because no influences can propagate faster than the speed of light. The force you are applying is electromagnetic, so the protons and electrons in your hands will be exerting electromagnetic force against the photons and neutrons in the ball and causing it to compress.
In fact, it is probably going to be a lot slower than the speed of light because effectively you are sending a sound wave down the tube and the speed of sound is actually the fastest information can pass through a material elastically. With something like a steel ball, it is about 5 or 6 kilometres a second, much faster than the speed of sound in air but still, very very slow compared to the speed of light.

4. When we get scared, some physical changes take place in our body. How does this happen?
Ans: When something scares us, a signal is sent to our amygdala which is a part of the brain that controls emotion. The first signal that is sent actually bypasses the conscious part of your brain and that explains why if you glance at a piece of rope out of the corner of your eye, you get scared before you consciously see it and realise that it is not actually a snake. It is just a piece of rope, but that fear comes before that realisation. The second response is slower and travels through the cortex and that gives you the conscious control and the realisation of, “Oh, it’s just a piece of rope. It’s not going to hurt me.”
Now, if it had been a snake you had seen, the feeling of fear would have also been accompanied by what is known as the ‘fight or flight’ response, and that prepares you to respond to danger.
Your sympathetic nervous system becomes activated and this releases adrenaline into the bloodstream. Your pupils dilate, allowing more light into your eyes, your heart rate and your breathing increase, sweat is produced and digestion stops. Cortisol, which is known as the stress hormone, is also released and this increases glucose levels in your blood to provide extra energy, and all of these things that will prepare you to either run away from the source of the fear or to attack it, to fight back.
In modern life, those two options are not always possible. If the source of your fear is going on stage on school day or something like that, then running away or fighting it are not really options. So, in this case, these mechanisms which evolve to protect us may actually be detrimental to our health. Prolonged stress responses of this kind are bad. If you stay at this heightened level of arousal, of fight or flight, for a long time, it can actually weaken your immune system and increase your blood pressure, so it can make you more susceptible to colds and flus, and also increase your risk of heart attack. So if you do have a very stressful job or life, or you get scared a lot, it is probably a good idea to try and take a break every now and again, let your body calm down a bit and recover.
Short levels of such stress can actually be quite beneficial. It can make you perform better. A lot of performers find that if they do not get a bit of nerves before they go on stage, their performance suffers. This is an inverted U-shaped curve. There is a beneficial level uo to a point, and then if it goes above that, it starts being detrimental again. So a short burst can be good, but a very high level of adrenaline release for a very long period of time is bad.

5. What would happen to the Earth if a meteor hit the moon and destroyed it?
Ans: The short answer is that we would have a *nuclear winter*. It would put huge amounts of rock into the atmosphere, which would block out the sun.
If the meteor hit hard enough to blast the moon into millions of pieces, then there would be enough energy that a significant portion of the moon would land on our atmosphere. You will get huge amounts of dust in the atmosphere. All the plants would die.
We would have a buffer against solar influx, and this would cool down the Earth -- not by a bit, but a million times over. The Earth would be a pretty nasty place.
The other question is if somehow the moon simply disappeared, what would happen? We would immediately lose the tides because those are due to the moon’s gravity. Also, on a longer term, there would be some subtle effects; the axis of the Earth is actually stabilised by the moon orbiting it. The moon has got a large angular momentum, so perturbations do not tend to have a very large effect on it and it tends to stabilise the direction of the Earth’s axis over millions of years.
So, if you then waited millions of years, the Earth’s axis would rotate and that could have all sorts of complex effects on the weather and life in general and also not having tides could have all sorts of strange effects on weather because you are not mixing the oceans. Remember that the oceans move far more energy around the Earth than the atmosphere does. 
Thus, either way, it is not a good idea to bother the moon.