Our moon is "gravtiationally locked" to the Earth (it's also sometimes called "tidal locking, but I think that phrase is potentially confusing). This means that only one side of the Moon is ever facing the Earth, but what would happen if the Earth was locked to the Sun?
Several things would happen. The obvious outcome being that one side of the Earth would gradually absorb the Sun's radiation, while the other side would get practically none. The entire planet would end up with one blisteringly hot side and one very cold one.
Where this gets interesting is if we consider life. Life on Earth needed liquid water to evolve. The chemicals we're made of have to be able to move around in order to transfer information and react with each other, that's why life is never found in water-less environments.
On our locked Earth, the only place liquid water could form would be on a thin band around the rim of the planet. On the "hot side" the water would evaporate, while on the other side all the water would be frozen as ice. No life would form on either of the two hemispheres. What's more, the hotter side of the Earth would also end up with lots and lots of heated air moving around, leading to crazy storms.
The life which did arise would be confined to a thin rim a few dozen kilometers wide stretching all the way around the planet. When life did arise there, it wouldn't have much room to spread out, meaning evolution would take longer to happen. As a result, the creatures which did manage to exist would be totally different from anything living today.
Ultimately, you exist in your present form due to mutation. It's the driving force of natural selection and the reason we aren't all single-celled creatures living in rock pools. When the DNA in your cells (the biochemical which tells the rest of your body how to be structured) gets copied to make new cells, it gets mutated in the process, causing new features in you, the person.
When a DNA strand is split and copied, there are several steps and several different "enzymes" (biological machines) in charge of different stages of the copy. Rather than a smooth photocopying process, there are at least 9 known parts to the copying process, each with its own enzyme. If something goes wrong during this complex copy process, we end up with a mutation/new sequence in the DNA sequence.
There are two main types of DNA mutation: Substitution (where one of the DNA building blocks is swapped for the wrong one) and Frameshift (where an extra block is added, or an original block is missed out, and the entire sequence is out of alignment.
There are four main sources of DNA mutation:
1) Simple copying errors. With so many chemicals floating around, winding and unwinding about each other, it's no surprise that sometimes the wrong building block gets inserted into the DNA. The four building blocks available are called A,G,T & C and they're all fairly comparable in size, so they can get mistaken for one another without anything being too badly misshapen.
2) Mutagenic chemicals. There are some substances which can leak into a cell and alter the copying process e.g. damaging the copying enzymes or causing the DNA strand to buckle and twist in the wrong way.
3) Natural decay. DNA isn't a robust chemical. In fact it's quite fragile. Parts of the strand will naturally decay, fall apart, ionise, bind to solvent etc. and give us unfamiliar structures, leading to new inaccurate copying.
4) Cosmic rays. Space is filled with small nuclei of elements flying at incredibly speeds. They zip around the galaxy, ionising molecules and initiating chemical reactions. Astronauts sometimes pick these things up with their eyeballs, seeing bright flashes appear in their vision. The source of these particles (cosmic rays) is unknown, but their effect is well documented. On Earth our magnetic atmosphere (magnetosphere) largely protects us from these rays, but one in every few thousand make it down to Earth. If they enter a cell, they can ionise it, meaning it will be mistaken for a different chemical and voila - more mutation.
The user Perran already gave a very good answer to this question, I'm just going to go a notch further and take it to some extremes. There are really two things to consider, there's your "weight" which is the Force of gravity pulling you toward Earth and your "apparent weight" which is really how pulled down you actually feel.
Imagine floating in a lake, gravity is pulling you down the same as it would on land so your actual weight hasn't changed at all. But floating in water seems different to standing on land. It's because on land, the ground beneath your feet is being squashed - all those atoms you're standing on are being crunched together like little springs so they're pushing back up on you, providing an opposing force. Your "apparent weight" is this feeling of the floor pushing up on you. But when you get into water, you sink into it a bit and it doesn't squash up against you as much, so you don't feel as heavy.
Or imagine being in a lift. As the lift moves upward, you feel heavier, it's because the ground is pushing into you more, so your body feels more of a Force from below, making your "apparent weight" (i.e. the force between the ground and you) pretty large. If the lift were to start falling, the ground beneath you wouldn't be pushing up anymore, so you wouldn't feel yourself getting squashed against the ground, giving the apparent weight of nothing.
So when you're in free-fall, that feeling of rushing toward the ground is your weight pulling you, but there's nothing squeezing back up into your feet (no ground surface) so you feel completely weightless. In reality you still have lots of weight, that's what's making you move, but your apparent weight is essentially zero (apart from the air particles bumping into you)...and from there we can go into Perran's answer which explains terminal velocity nicely!
First thing we need to talk about is the length of a wave. A high energy beam of light has a short wavelength because all the energy is compacted into a small space, while a low energy beam of light is spread out and loose. Colours like blue, green and UV have shorter wavelengths (more energy) while red and IR have low energy. (Note to the reader: my dad works on lasers, so he knows all this, I just put that bit in for everyone else)
But how come IR feels warmer if it has less energy than visible light?
The answer is actually part Physics and part Biology. Different sizes of wave will interact with atoms in different ways. Radio and Microwaves, for instance will impact an atom or molecule and make it spin. Infra-red, packing a bit more punch, will make the bonds stretch and twist (more of a change to twist something than to simply rotate it). Visible and UV light are the same size as the electron shells, so they make the electrons on the outside of the atom/molecule dance around. X-rays will make the core electrons right near the centre of the atom dance, and a gamma ray is so compacted in energy that it will actually make an atom's nucleus vibrate.
So different amounts of beam energy have different effects on what it's hitting, roughly corresponding to size i.e. large waves will interact with a whole molecule, tiny waves will interact with the individual nucleus. Infra-red (and microwaves) happen to be the ones which bend, twist and stretch molecules.
In human skin we've got tiny sensors called "thermoreceptors" which pick up on the vibration energy of the surrounding cells. If I.R. waves are hitting human skin, the molecules in skin will twist, vibrate and stretch, triggering the thermoreceptors which sends a signal to the brain as "hot". Visible light, while packing more energy, just causes the electrons in the skin-molecules to dance around, a more impressive feat, but something the thermoreceptors don't pick up on.
So while IR is much lower in energy than visible light, our skin doesn't have sensors to pick up on electron dancing, only molecule twisting. So our skin-linked nerves detect IR but not visible light. By contrast, the human eyeball has chemicals which do pick up on visible light making the electrons vibrate, but not IR, that's why your eyeballs never feel hot!
Most of the time when you dream, everything seems completely normal. But when you wake up, you remember that you don't live in a castle, your auntie isn't actually a horse and you can't really play the bongos...annoyingly. You don't usually know you're dreaming while you're in the middle of a dream. But some people are able to not only realise they are dreaming, halfway through the dream, but control it and enjoy the dream on their own terms, this is called lucid dreaming.
Nobody knows for definite what is happening when you get a lucid dream but the most likely explanation is the following: When you enter sleep, certain parts of your brain get switched off, usually the parts involved with common sense and logic. But in some people (or in people who practice) it's possible to keep one part of the brain active: The Dorsolateral Prefrontal Cortex (DLPFC)
The DLPFC is a part of the brain involved with long-term memory. It helps you remember where your house is, how to write and what your friends names are. If this part of the brain is activated (rather than switched off) it can sometimes notice something in the dream doesn't match real memories. It will suddenly go "wait a moment, this isn't what the world is really like, I remember the real world" and your brain realises that what you're thinking about is fake; a dream.
Good question, although I'm afraid the answer is only pseudoscientific. I modelled the logo after a chemical element symbol. Typically you express the mass of an atom with a decimal point because it's an average of masses. You take all the different versions of an atom and the average mass is what ends up on the PTofE. There aren't multiple versions of me (that I know of) so that number isn't an average of my mass. My mass is 70 kg but 70 on its own looked boring.
The symbol at the top is not a trident (as some of my Physicists suggested). It's a greek letter psi and it's used in Science to represent what's called a "wavefunction" - a full description of a particle/group of particle's behaviour and state at any one point in time. I, as a collection of particles, can be described by a wavefunction, hence the choice of symbol!
Although it sounds like a Biology term, this comes from nuclear physics. When we're talking about a particular type of atom in Chemistry we are talking about a nucleus and the electrons orbiting it.
But sometimes in Physics we talk exclusively about nuclear reactions i.e. a nucleus changing from one type to another. In this instance we ignore the electrons around the outside of the atom. We tend to use the word "nuclide" at this point, the same way we might refer to different chemical elements, or chemical species. We refer to different nuclides to mean the different nuclei in a process.
Nuclides can turn from one type into another by lots of different routes. Alpha decay, Beta decay, Beta capture etc. These nuclear reactions will generate a new nuclide (a new nuclear species) and they began with other nuclides. They are nuclides generated by other nuclides "nucleo-genic nuclides".
By contrast, some nuclides are made as a result of cosmic rays bombarding a nucleus, creating a new nuclide species. These nuclides are called cosmo-genic nuclides. Nuclides generated by cosmic ray interactions.
My brother asks: If substances contract when they get colder (Charles' law), why is ice less dense than water?
My (far more observant than me) brother noticed something interesting in the first video I posted about Charles' law. In the video I talk about how cooling something down will make it take up less volume because the particles take up less space. But that's not what ice does, it's well known to expand by about 9% when it forms. So what's going on?
The answer is that Charles' law applies to what's called an "ideal gas", that is, a gas in which each particle flies about without interacting with anything else. As you cool them down the particles start squashing and we get less volume etc. etc. But here's the thing: water isn't an "ideal" gas because water molecules interact.
Water molecules act a bit like magnets, boomerang shaped magnets. When they've got lots of energy they roll and tumble over each other in close proximity; they have enough movement energy to make the attractions between them too small. But if we cool the water down, the molecules move around less and the attractions between them start to become the dominant effect. This means the water molecules snap together into a crystal-grid shape, with gaps in between each molecule. This structure takes up more space than the liquid water.
Water is one of the few substances on Earth which don't obey Charles' law. Plutonium is another, as is silicon dioxide (the main ingredient in sand). These substances do get smaller as you cool their gases down, then even smaller as they condense, but then they get bigger again in the solid form. Keep cooling things down and the ice rearranges once more to make a smaller type of crystal, and then smaller and smaller. So water does eventually follow the same rules as every other substance, but it takes a bit of a detour around zero degrees.
The answer is yes absolutely, we're already closer than you might think! In the last few years Chemists have been experimenting with a newly developed substance called graphene. It conducts better than copper, is tougher than steel and (here's the really cool bit) it's one atom thick. At present the research is in its early stages but people are looking at making circuit boards out of graphene and putting them into our technology... creating super thin circuit boards. We already have the technology to put a camera into a contact lens, so thinner smartphones may be next.
A day is the time it takes the Earth to spin once. It does this about 365 times as it goes round the Sun. So 365 days is the number of spins it takes for Earth to make one complete orbit. The reason it happens to be exactly 365 is completely random! There is nothing special about the number 365. The planet Mercury, for instance, takes 88 days to do one lap of the sun, so it has an 88-day year, while Mars takes about 687.
As to why a day is 24 hours, this is something we've inherited from the ancient Egyptians. About 4500 years ago, Egyptians were using sundials to measure time. For some reason nobody really knows, they decided to split a day up into 12 equally sized portions, what we now call "hours". So there are 12 of them in a day, then another 12 at night. This method of splitting an Earth-spin into 24 chunks has stuck mostly by accident. We could just as easily have chopped a day up into ten pieces and had a decimal system of time!