Tag: heat transfer

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Sweaters for Squirrels

Sweaters for Squirrels

I got a call from a lady who was making sweaters for squirrels. She was concerned that the cold weather would make the squirrels shiver and get sick if they didn’t have protection. I tried to tell her that her heart was in the right place, but God had already made wonderful coats for the squirrels. Because of that, they do not require winter clothing to add to what God had already given them. That led to a discussion of birds who didn’t have fur coats. I asked her if she knew about goose down, and she admitted she had a goose down winter coat. “But those poor little birds on my feeder don’t have down,” she replied, “and I have seen them shiver.” Sweaters for birds seem to be more problematic than sweaters for squirrels.

That exchange started me thinking about the many ways God has equipped living things for cold climates like the one here in Michigan. When I taught physics in the public high schools of South Bend, Indiana, we covered conduction, convection, and radiation. I began the discussion on conduction by asking why we wear clothes, outside of the obvious one. The thermal conductivity of various kinds of clothing helps us stay warm in winter and cool in summer. For example, goose down is a good insulator because it holds pockets of air, and air does not conduct heat well. Likewise, the design of skin and hair involves thermal conductivity, which is why being immersed in cold water takes heat out of our bodies rapidly, causing hypothermia.

Fat is another insulating material, and having very little fat in one’s body can cause rapid heat loss. Even the color of one’s skin or hair can make a difference. One of the experiments that I had my students do was to take two identical cans and paint one black and the other white. We would then put boiling water in each can and measure the temperature of the can every minute, graphing the cooling curve of the two cans. The black can would cool much faster than the white can; in this case, the cooling is by radiation, another heat transfer method. We all know that black objects absorb heat from sunlight better than white objects. Therefore, black things also release heat more rapidly.

The physics of heat transfer is another design feature built into living things. All animals are designed with the right equipment to survive in their natural environment. That is why we don’t need to make sweaters for squirrels. However, when humans move animals to a radically different climate, the result can be dangerous.

Climate change is causing some animals to migrate to latitudes where their survival is not threatened. That is also a design feature of life. In Job 39, God challenges Job with questions about design features in living things. We are only now beginning to understand the answers to some of those questions.

— John N. Clayton © 2022

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Moving Heat Energy

Moving Heat Energy
Winter always reminds us of how important it is to have ways of moving heat energy from one place to another. We are considering how the complex heat transfer system is another evidence for God’s creative wisdom. Yesterday we looked at heat transfer by radiation. There are two more methods.

A second way of moving heat energy is by conduction. When you put a spoon into a hot cup of water the molecules that make up the spoon begin to vibrate faster as they absorb heat energy from the water. As one molecule gets energy, it bumps into the next molecule, and it also starts to vibrate. This happens down the length of the spoon, and eventually, the heat is conducted to your skin.

How fast heat conduction happens depends upon the size, mass, and density of the material in the object conducting the heat. Gases have poor conductivity because their molecules are far apart. A winter coat has lots of spaces between the fabric molecules filled with air. Fur has air spaces between the hairs and inside the hair strands themselves. Those low-density spaces insulate against heat transfer. You have heard the old story about never putting your tongue on a very cold metal object. The reason is that the water in your tongue conducts heat away to the metal surface which is very dense. The heat transfer process happens so fast that the water in your tongue freezes.

A third method of moving heat energy is by convection. Heating air or water is difficult by radiation alone or by conduction alone. The materials are transparent, so they absorb radiation poorly. Conductivity is slow and limited as to how far the heat can travel. What happens is that molecules change their density as they are heated or cooled. When heated, the gas or liquid becomes less dense it rises taking heat energy with it. As it cools, it sinks because it becomes denser. The motion mixes the hot and cold in the process we call convection.

The amazing ability of water to change its density as it is heated and cooled allows lakes to form ice on the surface rather than on the bottom. Water was designed to have its lowest density at 32 degrees Fahrenheit. It has a higher density both above and below that temperature. A very complex chemical property of water is designed to handle the heat energy by becoming more dense down to 32 degrees and then less dense as it freezes into ice. You can read more about this essential characteristic of water in THIS PREVIOUS POST and in our book Dandy Designs Volume 3, available HERE.

We take for granted the various methods of moving heat energy in and around us, but the complexities of this design are amazing. My physics students love to see how this allows us to exist on this planet.
–John N. Clayton © 2019

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Heat Transfer Design

Heat Transfer Design
During this time when record cold temperatures have covered much of the United States, we should consider the design of heat transfer. One of the evidences for the existence of God is the wisdom built into the physical creation that makes it possible to move energy. God created a system of heat transfer design that is far more complex than most of us realize or can imagine.

The primary source of heat for the surface of our planet is the Sun. The question is how heat from the Sun can travel 93 million miles to Earth through what is essentially a vacuum. Realize that there is no substance between the Sun and us, so the heat can’t travel by contact. Atoms are constructed in such a way that they release excess energy by generating small energy packets called photons. Photons from the Sun carry the energy to Earth.

Photon particles are very strange. They have an electric property and a magnetic property, so they are called electromagnetic radiation. Photons have no thickness. They are two dimensional, vibrate with a frequency, and can exist only if they are moving. If you stop a photon, it disappears, and its energy is absorbed by whatever it struck.

Because photons are particles, they can travel across the vacuum of space from the Sun to the Earth. Their vibration frequency determines how we perceive them. We have different names for the frequencies. Xrays, gamma rays, ultraviolet, infrared, radio waves, and visible light are different only in their frequencies. The higher the frequency, the more energy is involved. Gamma rays have a much higher frequency than visible light, so they pack more energy.

Everything radiates some energy, even our bodies, but this is just one way heat is transferred. Besides radiation, heat transfer design also involves conduction and convection. We take for granted the various ways in which heat is transmitted in and around us, but the complexity of heat transfer design is amazing. It is that design which allows us to exist on this planet. We will look at the other two heat transfer methods tomorrow.
–John N. Clayton © 2019