Both Alberto and I love the snow.

I go skiing and he goes snowboarding and as we haven’t ever been together in a snow trip I’ve decided to share some of how this activity looks like to me.

When you are a scientist you wake up in the morning in a nice village a few kilometers away from the ski resort, let’s say in the Pyrenees, you look up at the sky and then you wonder:

How can there be clouds in winter when it is too cold for water to stay as a vapor?

Although clouds look like they are made out of vapor that’s not true. You may notice when cooking that water vapor is invisible… so, why would that be visible on clouds? Water vapor is invisible because its molecules are too far apart to optically scatter light so there has to be something else inside the clouds.

Whenever you see steam, mist, fog, or clouds, you are seeing small drops of liquid water or ice, and not water vapor. The water drops in the air are usually too small for you to see them individually, so instead you see a white or gray haze. This is called optical scattering.

Clouds are not always drops of liquid water. Clouds can also be composed of ice crystals. In fact, the same cloud can be partly composed of water droplets and partly composed of ice crystals. Clouds have no problem existing in the cold of winter, because they can just exist as ice crystals. In fact, even in the summer some of the clouds you see are composed of ice crystals. A lot of the rain drops in the summer started high in the sky as snowflakes but melted before reaching us.


It’s really cold. So cold that you leave the house and you can see your own breath.

Why do we see our breath in winter?

With every breath you exhale, you are blowing out water vapor that has evaporated from your lungs. You don’t usually see your breath because the vapor you exhale stays in the gas state. But when the air outside is cold enough, the water vapor you breath out quickly condenses to little drops of liquid water and you see your breath as a small cloud.

So you go to the car, and the driver may be a bit late, so stay inside, chatting with the rest of the gang and the windows start getting foggy.

Why car windows get foggy?

Hot air can hold more water than cold air. So when hot air, rich in water vapor touches a cold surface, it can’t hold as much water anymore and condensation occurs. When this happens in your car the condensed vapor on glass windows causes fogging.

When windows are closed and passengers are sitting inside, the air inside the car holds plenty of vapor due to people breathing.

To get rid of the fog you have two options: turning the heater on or opening the windows.

– Turning heater on increases the temperature of glass windows to slow down condensation.

– When you open the windows, you are letting outside and inside air mix. Water vapor can now escape outside and this reduces the amount of humidity inside the car. As a result condensation slows down.

Then it’s time to drive to the ski resort, and suddenly, out of nowhere, the car slides. There is black ice on the road!

What’s Black ice.

Black ice, or clear ice is a thin coating of glazed ice on a surface. While not truly black, it is virtually transparent, allowing black asphalt roadways or the surface below to be seen.

Black ice forms when light rain falls on a road surface whose temperature is below 0 °C

Fortunately you find a gritter spreading salt.

spreadingWhy do we spread salt on icy roads?

Ice forms when the temperature of water reaches 0 degrees Celsius. When you add salt, that temperature drops: A 10-percent salt solution freezes at -6 C, and a 20-percent solution -16 C. On a roadway, this means that if you sprinkle salt on the ice, you can melt it. The salt dissolves the ice into liquid and lowers its freezing point.

If the temperature of the roadway is lower than -9 or so, then the salt really won’t have any effect because the solid salt cannot get into the structure of the solid water to start the dissolving process. In this case, spreading sand over the top of the ice to provide traction is a better option.

You have now arrived at the resort and it’s time to rent a pair of skis or a snowboard table. Do you know which length is better for you? Physics is here to help!

How to choose a pair of skis or snowboard length.

Usually somebody at the station helps you choose the appropriate length. The general rule is to pick a ski length that is somewhere between your chin and the top of your head and board between your clavicle and your chin.

But there are a couple of things you should also pay attention to, like your weight and your level. Because when you are skiing or snowboarding there is only one thing to stop you: friction!

The longer the skis or the board the less the pressure you are making against the snow and friction is something dynamic that changes with that pressure.

So if you are a bit overweighed you should take longer skis or snowboard. The opposites applies as well; if you are really thin a shorter size may help you.

For the same reason beginners should use shorter sizes than advanced.

Finally… if you are going to race someone pick the longest!

Why are no two snowflakes exactly alike?

A snowflake begins to form when a very cold water droplet freezes onto a dust particle in the sky. This creates an ice crystal. As the ice crystal falls to the ground, water vapor freezes onto the primary crystal, building new crystals around.

Individual snowflakes all follow different paths from the sky to the ground and they encounter slightly different atmospheric conditions along the way. Therefore, they all tend to look unique.


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