It’s 19°F (-7.222°C) outside, but I see that snow is melting. How is that possible when it’s below freezing?
In: Physics
the temperature of the earth’s ground surface or of the object may be above freezing, while the air is a lower temperature. some surfaces, like cement, retain heat.
Even though the general temperature is low, the energy from the sun that directly hits the surface of the snow is still enough to melt it.
Two things
1 – It’s possible for the air temperature to be one thing, but an object’s temperature to be another. I’m sure you’ve experienced this on a sunny day, where it feels much cooler in the shade than in the sun. The air temperature is the same for both, but when you’re sitting in the sun you’re absorbing solar radiation, which is warming you up.
2 – Temperature relates to the *average* kinetic energy of particles in a material. There is actually a distribution where some particles are moving much faster and some much slower. Some of those higher energy particles can collide with the snow and impart enough energy to melt snow. Statistically, this is happening over and over again enough for the snow to melt.
Because although the ambient temperature is below the freezing point, the sun can heat the ground above the freezing temperature. I would wager if you took an IR thermometer and measured ground/surface temp of objects you would find they are above the freezing point.
Not that this answers your question further, but this brings up the fact that water is honestly one of the most interesting substances on the planet in that it can remain liquid below its actual freezing point. This is because to freeze, the water molecules must stop moving. So, a river can continue to flow well below 32F. We have actually observed liquid water in clouds at -40F, and we have been able to achieve -42F in labs. I believe (don’t quote me here because I can’t remember perfectly) that water does not HAVE to freeze until around -55ishF.
Latest Answers