Tuesday, June 26, 2012

Water and Specific Heat Capacity

It's not a coincidence that about 80% of the human population lives within 60 miles/100 kilometers of an ocean margin. Spend a winter (or a summer) in an interior state like Kansas, or Kazakhstan, and you will understand why they are not crowded. Temperatures in Fairbanks, Alaska, can range from 86F/30C to below -60F/-50C between Summer and Winter - and that's above the Arctic Circle! I've personally experienced temperatures of 130F/50C in Arizona and 142F/61C while working in the interior of Saudi Arabia.

We would have occasional snows (and freeze rain) when we lived in Virginia. That wasn't so bad... But sometimes we do not even see snow during the winter in Vancouver, and it's notable when the temperatures get much above 75F/24C.

I could easily get used to this. I think I'll stay...

There's a downside to this, of course (there always is, isn't there?). Populations close to a seashore are much more vulnerable to a tsunami from a seafloor fault rupture - or an asteroid impact in the ocean. Volcanoes can even figure into the Coast is Toast picture: the tsunami that resulted from the explosion of Krakatau in 1883 traveled more than 10 kilometers inland onto neighboring Java and Sumatra islands... then swept everything it had picked up and took it all back out to sea. Contemporary accounts mention being able to walk across the Sunda Strait on logs and bodies without getting your feet wet.

There is a reason for that very human tendency to hug the coast, and it's not for the sandburgers and grit-flavored potato salad. It's because of the moderating effect of nearby oceans. The key to that effect is the specific heat capacity of water - it is more than 4 times greater than air. In other words, it takes more than four times as much energy to increase a unit mass of water by one degree C than it does to raise the same mass of air by one degree. That means that the oceans act like a thermal buffer - because they can absorb and release so much heat without much of a temperature change.

Bottom line: ocean temperatures don't change much.

We notice the effects of water on temperature in a number of different ways, and the next series of questions raises an unusual issue:

Does an object traveling under water get colder as it increases it speed through the water? Similar to a wind chill factor. 
- Gaylord M.


Yes - if the water is colder than the object moving through it.

Water has a specific heat capacity of 4.2 with respect to air. This means it can hold - and transfer - far more energy than air for just one degree of raised or lowered temperature. The faster you move through a medium (like water) that has a different temperature, the faster and more effective is the thermal exchange, all other variables being constant.

Most people know that getting into cold water will chill them much faster than walking through air of the same temperature. I noticed when I lived near the Red Sea that if I went diving in temperatures below 82F/28C, that I would quickly become hypothermic. This hugely different heat capacity is also why it is so important to wear clothing that keeps moisture away from your skin as much as possible.


Thanks for the reply. I asked the question, as I was wondering if it could have had an effect on the Titanic's rivets to cause them to fail. I had watched a segment on the History channel where they had ran some tests and determined the rivets had not failed. However they were running their tests in what appeared to be a normal environment. Only one of the test rivets failed.


The possible effect of ice-temperatures on the Titanic's rivets is an interesting thought. I'm not a metallurgist, but have watched, with interest, several back-and-forths in the semi-scientific literature about the possible "failing Titanic rivets" issue.

In this case I don't think the temperature would have made much difference, because North Atlantic water ranges between 0C and 22C, depending on the month.

That's not really much of a temperature difference, considering the temperature that the rivets were forged at, and the fact that the ocean temperature cannot go below the freezing point of ice. Because of water's large specific heat capacity, there really is not much of a temperature change in the North Atlantic.

There were literally thousands of steel-riveted ships plying the North Atlantic during that epoch, and it makes more sense to worry about metal impurities in a given production batch of rivets than in the narrow temperature range that they would operate under.

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