How does snow form?

How does snow form?

High up in the atmosphere, the air temperature is very cold. The water vapour may fall as rain if the water does not freeze. However, if the air temperature is so cold that the water droplets freeze, tiny ice crystals form in the clouds. These ice crystals collide with each other in the clouds or grow delicate shapes. The ice crystals combine to form snowflakes. There may be hundreds of tiny ice crystals in a single snow flake. These snow flakes fall from the clouds to form snow on the ground.

If the air temperature is not too cold and the air is very moist, the snow flakes may grow into very large flake up to 1 or 2 centimetres across.

Every snow flake is different. However, each snow flake has 6 sides.

What is sleet?

What is sleet?

When the air temperature is very cold, water vapour in clouds may fall as sleet, hail, or snow. Water droplets in the clouds get cold, but may not freeze completely. Sleet forms when partially frozen water droplets, or rainwater, in the clouds falls and freezes completely when it hits the surface of the Earth.

Like freezing rain, sleet may be dangerous because it coats roads and sidewalks with ice. Cars may not be able to stop on the slippery roads and many collisions between cars may occur. Slippery sidewalks are very difficult to walk along.

What is freezing rain?

What is freezing rain?

When the air temperature is very cold, water vapour in clouds may fall as sleet, hail, or snow. Water droplets in the clouds get cold, but may not freeze. Under certain circumstances, the temperature of the water droplet may drop below the freezing temperature of water, but the water remains in the liquid state. This water is super-cooled. When super-cooled water falls to the surface of the Earth, the water freezes instantly on any surface it hits. This is called freezing rain.

Freezing rain may cause lots of damage. Trees and power lines may break under the weight of the heavy ice. Cities may have to go without electricity when major power lines are broken.

How do clouds form?

How do clouds form?

As warmer air pass over the ocean or large open lakes, the air picks up water vapour. As the air warms, it rises because warm air is less dense than cold air. As the warm air rises, the air cools and the water vapour in the air condenses to form clouds of water droplets.

Clouds that form at the surface of the Earth are known as fog.

What is potential energy?

What is potential energy?

Potential energy is stored energy. An apple sitting on the edge of a table has stored potential energy. The potential energy changes to kinetic energy when the apple falls to the ground. A compressed spring has potential energy. That potential energy is converted to kinetic energy when the compressed spring is released.

What is energy?

What is energy?

Energy is the capacity to do work. Our energy comes from food, which contains stored chemical energy. Our bodies take the stored chemical energy and converts it to mechanical energy, heat energy or other forms of energy.

Light, sound, heat, and electricity are forms of energy

How does the sun produce photons?

How does the sun produce photons?

The surface of the Sun is very hot of course. It’s so hot that hydrogen becomes ionised into plasma so that you have photons and electrons as separate bodies, rather than bound together into atoms. And as those different charges interact, they exchange energy at the surface of the Sun and in the process of saving energy, they can lose energy and that is radiated as the photons that we see. Now that's not actually the powerhouse that drives luminosity of the Sun. That is the fusion of hydrogen atoms into helium which occurs at the core of the Sun. In fact, only in the central 20% or so of the Sun and so, you have another process which is convection which is carrying that heat which is generated at the centre of the sun out of the surface to keep the surface hot so that it continues to shine.

Are there no photons being produced deep inside the Sun? Presumably there are, but they just can't get out.

Photons are being produced all throughout the Sun, but the Sun is made of a cloudy material because these protons and electrons can interact with that light. And that means the photons produced deep down can only actually travel a few centimetres before they're reabsorbed.

And of course Bryan Fulton who was on this program, he’s professor of Astrophysics at the University of York. I think the point he made was that the photons that get made in the Sun are actually a million years old plus by the time they emerge because they have spent their entire life being bombarded around and absorbed and reabsorbed, ad infinitum almost before they finally escape. So if the Sun went out tomorrow, went out as in all reaction stopped, we’d still have a million years of the light locked inside.

The light is travelling at the speed of light, but it’s only hopping a few centimetres at a time and we don't know what direction it’s going to come back out again. It may end up going back towards the centre of the Sun again and it takes a million years. It’s quite a random walk for that energy to get to the surface.

Are air cavities in the body a problem when diving deep?

Are air cavities in the body a problem when diving deep?

It is a very good film and it does seem very futuristic, but it is actually partly reality. These chemicals, these liquids do exist. They're called perfluorocarbons. They include fluorohexane for example, so a string of 6 to 8 carbon atoms with lots of flourines hanging off the side and they're very good at dissolving oxygen. So, one way of doing this would be to instil these fluids into the respiratory tract and you saturate them with the oxygen, and then you move the fluid in and out, in the same way that you would when you were breathing.

Why this is helpful is that when a person descends underwater, the pressure they feel from the surrounding water goes up and up, the deeper they go. So, you have to therefore put the gas into the lungs to keep the lungs inflated, under progressively higher and higher pressures. One consequence of this is that it drives other gases like nitrogen and things into the tissues at extremely high pressures which means that then when you decompress, those gases come out of solution in the tissues and form bubbles which can cause the bends, they can cause damage to the brain, and cause damage to bones and muscles and so on. So if you use a fluid in the lung, because fluids are incompressible then you wouldn’t have the same problem because the fluid would withstand the pressure being applied by the outside water much better.

The issue with these fluids though is that they're not very good at removing CO2. They're very good at putting oxygen in. They're not good at getting carbon dioxide out and to compensate for the fact that they don't move CO2 very well, you'd have to move a lot of the fluid a lot of the time, and that's one of the major hold ups with doing this. In terms of the liquid getting into other body cavities and body parts, this isn’t such a problem actually. The eustachian tubes that you mentioned, they run between the back of the throat and the ear, so they would just fill up with the fluid anyway. The other body cavities, well, they wouldn’t actually be exposed to the fluid directly because it will be in the respiratory tree. So, there wouldn’t be a problem there and if there were any leakages of the fluid into other places, you would just pass it, I would think. It certainly wouldn’t become part of the systemic circulation, so it should be okay.

If dark skin absorbs more heat, why aren't native African people white, and Inuit people black?

If dark skin absorbs more heat, why aren't native African people white, and Inuit people black?

Logically, it should be the case that if you have pale skin it’s going to reflect more light and more heat and would be suited to warmer, sunnier places. But what is actually happening is people with darker skin have more melanin, more pigment, in their skin and this prevents the short wavelengths of light, the UV, from penetrating deep into the skin. It also means the skin can produce vitamin D in suitable levels. So if you live in more northern climes where there is less sunlight, so for example in the UK, then it’s much better to have pale skin which allows more sunlight to get into your skin and more vitamin D to be produced. Vitamin D is great for strengthening bones. Iit prevents you from getting diseases like rickets which would be very selective against a population if you were living in northern Europe.

UV radiation damages folic acid which you need for the development of the nervous system. If you get folic acid depleted you get diseases like spinabifida, so in continents like Africa where there is a lot of UV in the sunlight, if you don’t protect yourself with lots of melanin you will depete your folic acid, leading to an excess of neural tube defects like spinabifida and this would manifest in a cost to reproductive fitness in the population. So as there is so much sunlight, Africans can afford to have dark skin and still make enough vitamin D and not lose their folate but once you get up to the parts of the latitudes we live in, where it’s miserable all the time, vitamin D becomes the real problem. You need to make enough vitamin D and so you have to have pale skin. There’s so little UV because we hardly ever see the Sun anyway that it doesn’t become a problem from the folic acid depletion, neural tube defect perspective.

Are any viruses good for us?

Are any viruses good for us?

This may be true, despite that fact that most people think of a virus as being something that makes them feel awful! A recent piece of research in Nature by Skip Virgin, suggested that being infected by one of the family of viruses known as Herpes viruses, such as herpes simplex, which causes cold sores, Epstein-Barr virus, which causes glandular fever. When they infected mice with the rodent equivalent of those infections, the mice developed a much better immune system than mice which had ever been infected. To prove this, they exposed the mice to the bacteria which causes plague and also listeria, and they found these mice to be 100% protected against these bacteria compared with animals which had never been infected with a Herpes virus. When they studies these mice they found molecules called interferon gamma at a much higher level, and this molecule is known to stimulate the immune system.
They think that because we've been living with herpes viruses for millions of years, the body has come to rely on infection to provide additional gene function which our body no longer has. This stimulated the immune system and we get some benefit. It's almost a symbiosis, we give the virus a home and it gives us a better immune system.