The Mpemba effect (hot water sometimes freezes faster than cold water):
SOMETIMES, not always, hot water will freeze faster than cold water!
1. Why does this work at all
2. Why does it only work SOMETIMES?
As I understand it (and I may be misinterpreting this new model), a team of physicists think they’ve figured out why and I’m going to try to explain it here!
But first, a thought provoking question: who pays people to figure out why water freezes differently and how do I get that job!
A little background:
Simplistically stated, temperature is a measure of heat energy
– another way to describe temperature is as a measurement of the average vibration speed of molecular sized particles.
Particles are always vibrating and moving around chaotically, and when our hands touch an object that has a faster average chaotic movement (higher energy), those particles will bump into the particles of our hand, causing the particles in our hand to have extra energy (heat), and they will move, on average, faster. Our nerves sense this as the sensation of heat.
In short, anything that can add extra energy to the atomic particles in my hand, causing them to move faster, will be sensed as heat.
I already described one way that heat can be transferred into my hand, namely, by being bombarded by particles that are moving faster…this contact transfer is called “conduction”
It turns out that, for an object to cool down from a higher temperature, the particles in that object would have to make more total collisions with something cold, in order to cool down than an object at lower temperature. Here’s the catch, current scientific evidence seems to indicate that the hot water isn’t making enough extra collisions to account for its more rapidly decreasing temperature!
So, how does hot water cool down faster than cold water?
It turns out that there are two other ways to transfer heat energy: convection and radiation. For our purposes, only radiation is important. Radiation is how the sun warms the earth. It sends energy to the earth in a wavelength that can interact with atoms and molecules in such a way that they speed up.
So, how might hot water release more radiation than cold water?!
Water is made up of two atoms of hydrogen bonded to one atom of oxygen. These bonds are created by sharing electrons. Extra energy can be stored up in these bonds by stretching out the bonds (like a rubber band).
Some evidence is indicating that this energy stored up in the stretch ones of the bonds can be released as radiation when water is heated up, and this reduces the total energy contained by the water much faster than just collisions alone.
In proverbs 30:18 Solomon says,
“There are three things that are too amazing for me,
four that I do not understand”
He goes on to describe the mysteries of nature as he saw them at that time. I believe it’s important for us to continue to look for the mysteries in the world and marvel at them until we can understand them.
Put a check in the box next to another mystery we’ve all been amazed by, finally solved…maybe.
Mike Birkhead is a medical student at the University of Missouri School of medicine
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