Tag Archives: Thermodynamics

Newton’s Law of Cooling

One of Newton’s famous contributions to physics was his work in thermodynamics — the study of heat and energy flow. He developed a physical law that showed the proportional relationship between heat loss and the temperature difference between an object and its surroundings: Newton’s Law of Cooling. Despite its name, it can be used to show how an object will cool or heat in its surrounding.

Newton's Law of Cooling 2

It’s worth mentioning that heat and temperature are two separate — but related — values. Heat is a measurement of the total kinetic and potential energy stored in the molecules of an object, while temperature is a measurement of the average kinetic energy. Heat depends on the speed, the number, and the type of molecules. So while a cup of coffee may have a higher temperature than something like an iceberg, the iceberg is made up of so many molecules that it has more heat, and thus more energy.

Newton's Law of Cooling 3

Nevertheless, heat and temperature are related. As an object gains heat, its temperature will also increase. When talking about Newton’s Law of Cooling, it can actually be rearranged to create an equation to show the temperature as a function of time.

Law of cooling

Where Ts is the surrounding temperature, T0 is the initial temperature of the object, and k is a constant.

This equation looks pretty confusing, but all it essentially means is the temperature of an object will decay (or increase) to match the temperature of its surroundings. The change will happen quickly at first, but it will slow down as time goes on.

Newton's Law of Cooling

This theory allows scientists and engineers to correctly predict how certain materials will behave in different conditions. These types of calculations are done for anything from insulated coffee mugs to space rockets. They can then safely manufacture these to prevent any damage or harm.

Written By: Scott Yarbrough

Fireproof Balloons

If you’ve ever brought a match to a balloon (or been in our Atmosphere and Gases class), you know that fire and balloons don’t mix, but what if you could prevent a balloon from popping when it comes in contact with fire? The answer to this dilemma can be found in the simplest place: water. A little bit of water in a balloon that is otherwise filled with air can prevent it from popping when burned. To understand why, let’s take a look at what’s happening during a balloon and match collision.

With an ordinary air balloon, the flame heats up the skin of the balloon until it weakens, popping the balloon, but when that match is held against the water-filled part of a balloon, the skin doesn’t weaken or pop.

This experiment is all down to the difference in heat conductivity of water and air. Air is unable to conduct heat away from the skin of the balloon fast enough to keep it cool, resulting in a popped balloon. However, water conducts heat away much more effectively, cooling down the rubber and preventing it from breaking. Throughout this process, the hot water rises to the top, allowing the cool water to take its place, absorb heat, rise and continue in a cyclical current. Water also requires much more heat energy put into it before warming up than air, allowing it to maintain this current longer.

This current only exists so long as you heat the balloon from the bottom, and if you place the match on the side or air-filled section, the balloon pops normally. When doing this experiment, you may notice a black smudge where you placed the match, but this isn’t a burn mark; it’s actually just carbon deposited on the balloon from the burning match.

If this looks like fun, grab some balloons, a heat source, some water and an adult, and try it today!

Diffusion, Pizza, and You

If you were to take a freshly baked pizza and put you and it at opposite ends of a vault with no airflow at all, would you ever be tempted by its delicious aroma? The answer, it turns out, is yes! Even without the aid of air currents, the smell would spread. Nothing in the room appears to be moving, but at the molecular level, things are very different.

At room temperature, the molecules in stagnant air whiz around at insane speeds– over 1000 miles per hour! The air seems still because molecules are so light that nobody can feel them individually, and there are approximately equal amounts of them going in every direction. However, tiny particles (like the delicious pizza odor) can still get knocked around by these randomly moving molecules. The process of stuff spreading out due to the movement of tiny molecules is called diffusion.

Molecule TempThe experiment you see in the video has one obvious difference: we are looking at a liquid instead of a gas. The molecules in water are much more tightly packed, and unlike in a gas, there isn’t as much room for them to zoom around. This means the molecules aren’t moving at such incredible speeds, but they also aren’t sitting still. They bump into one another, rotate, and vibrate like crazy!

Diffusion in ActiojnThe amount of spinning, bouncing, and vibrating that they do depends on one thing: temperature. In fact, temperature is really just a way to measure how energetic the molecules are. In the container of warmer water, the food coloring spreads more quickly. This is because at higher temperatures, the more vigorous vibrating and bouncing of the molecules pushes the green food coloring around faster. The cooler water has calmer molecules, which do less to disturb the blue food coloring.

Notice that the food coloring never seems to regroup together. Diffusion is entirely based on random movements of huge numbers of molecules, so it always results in concentrated areas of stuff like the food coloring spreading out to fill the available area. This trend towards uniform distribution is called entropy.

DiffusionDiagram

Diffusion causes molecules to spread out from areas of high concentration to areas of low concentration. Image credit: UC Davis

Random movement of tiny things may seem inconsequential, but it’s actually incredibly important. It’s how plants hydrate, hot chocolate cools down, spaghetti noodles absorb water, and even how oxygen gets to the bloodstream. Even more important than all of that however, is that it lets you know when there is pizza nearby!

Liquid Nitrogen: Deep Freeze Science

It was a cold night in Russia’s Sakha Republic. Tiny Oymyakon, widely regarded today as the coldest town on Earth, was used to going about its business in near-arctic temperatures. On February 6, 1933, its residents braved the lowest temperature ever measured in an inhabited location: ninety degrees below zero, Fahrenheit.*

LNstairsArcticCold

The coldest place on Earth

Source: http://www.nasa.gov/sites/default/files/coldestplacerecords.png?itok=nAYJEo7W

In the most brutal corners of our planet, far from human settlement, the freeze is more intense. High on a ridge on the East Antarctic Plateau, in shadowy pockets explored only by satellite data, overnight temperatures bottom out around negative one-hundred and thirty-five degrees Fahrenheit. These are the coldest conditions ever recorded on Earth.

Earth, though, is a hospitable planet. For true frigidity, look to the outer solar system. Triton, an icy pink moon orbiting the gas giant Neptune, clocks in at nearly four hundred degrees below zero! On its surface, alien volcanoes blast their gaseous guts out in jets up to five miles high. The volcanic ejecta crystallize immediately and snow down to the frozen world far below. Evidence from Voyager 2 indicates that these giant plumes are mostly made up of nitrogen– the main ingredient in the air you’re breathing right now!

LNstairsTriton

Global color mosaic of Triton, documented by Voyager 2, 1989. Geyser plumes are visible as dark streaks.

Source: http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA00317

At three hundred and twenty-one degrees below zero, liquid nitrogen is colder than the most frigid Arctic night. It’s a cryogenic substance that would fit in with Triton’s weather better than our own. Nitrogen on Earth is usually a gas, but it’s possible to condense it into liquid form in the lab. As you can imagine, when air meets liquid nitrogen, its cools down fast. Water molecules in the chilled air condense into droplets visible as clouds or fog.

This might sound familiar! It’s closely related to the mechanism that causes clouds to form in the sky, a process we modeled in the lab not too long ago. Clouds are born when air cools down enough for suspended water molecules to condense. This is why you see fog when you push a warm breath from your lungs out into the atmosphere on a cold day, or when you bring something cold into contact with warm air.

Humid air, ripe with plenty of water molecules, produces extra-thick fog. Check out the cloud cover created by introducing liquid nitrogen into a damp poolside environment!

LNstairs3
*All temperatures quoted are in degrees Fahrenheit.

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