Pertaining to the President

An interesting read from the American Thinker- can thermodynamics really govern political campaigns? Paul Shlichta attempts to answer this question in his writing. It is important to note that this article was published prior to the American presidential election.

Read the article here

An Experiment

Set up 3 glasses, each containing water at a different temperature. One should be hot (not unbearably hot though), the other should be cold, and one should be in the middle at a lukewarm temperature. Stick one hand in the hot glass and the other in the cold glass. Wait for approximately 30 seconds until your hands experience the complete sensations of hot and cold. Then take each hand out of their respective glasses and put them in the lukewarm glass. What do you feel?

The hand that was in the hot glass should experience the lukewarm water as cold while the opposite will occur with the hand that was in the cold water initially. This shows how temperature is actually a figment of our imagination- our perception of hot and cold, high and low temperatures, are relative to what we have previously experienced. The an increase/decrease in temperature is what causes us to experience hot/cold. How would Goldilocks have fared with the three bears' porridge had she known about the outcome of this experiment?

Contemplating Cold

In light of comment recently made on a post, I thought it would be worthwhile to clarify the colloquialism "cold". Cold, as Alexia correctly stated, is the absence of heat. Therefore cold is merely an indication of a lack of flow of energy, occurring due to an absence of a difference in temperature. As you walk outside on a cold day, the atoms in your body give up energy to your surroundings. Your body temperatures tries to reach thermal equilibrium with your surroundings, that thankfully your heart and blood flow counteracts this. It prevents all of your internal energy from being released, but a significant fraction is still expelled, resulting in a sensation that is commonly identified as "cold".

Teaching Thermodynamics

The following video is an interview with Dr. Ian Beatty concerning methods of education in thermodynamics. Dr. Beatty is a professor of physics at the University of North Carolina at Greensboro who specializes in physics education. In the interview he provides insight as to the relevance of the internet in learning about and teaching thermal physics.

Checkout his website and his blog.

Melting Ice

As explained in the video, the filming and measuring equipment malfunctioned before all of the ice melted into water. I was able to take some photographs to document the rest of the process:

It can finally be seen that the temperature of the water (melted ice) returns to room temperature while the mass of the ice/water remains unchanged.

Talking Thermodynamics

The following audio clip is an excerpt from a discussion I had with Dr. William Gerace, a professor of physics at the University of North Carolina at Greensboro. He describes the oversights made by the general public in their concepts of heat and temperature.

Heat and Hands

Rub your hands together- palm-to-palm, back and forth. What do you notice? You should feel your palms becoming warmer- if you don't you may need to seek medical assistance. This feeling can be ascribed to phenomena discussed in previous posts. Do you think this sensation of warmth (notice how I avoid the word "heat") is due to work or heat? You should be able to recognize that the internal energy of the atoms in your hands is increasing, but how is this increase happening?

temperature pre-rubbing

initiating rubbing

rubbing hands together

finishing rubbing

temperature post-rubbing

Friction is the mechanism that caused this increase in internal energy. It can be seen that the temperature of my palms increased from 23.0 to 23.4 °C, a 0.4 °C difference. To calculate the energy involved in this process, one must first know the specific heat capacity of skin. Specific heat capacity is the energy required per unit mass to raise the temperature of a substance by 1 K or 1 °C. The specific heat of skin is  3.47 kJ/(kg*°C) (source).

Now we need to approximate the mass of the skin involved in the friction force. Knowing that the mass of human skin is 4.1 kg (source: yes, Wolfram Alpha is capable of computing the mass of human skin, don't ask me how) we can reason that skin on our hands is a small fraction of this total mass. Lets say that it is 1/1000, meaning that that the mass of the skin on our hands involved in the process is 4.1g.

We now know all the relevant values required to calculate the energy involved in the interaction:
change in temperature: 0.4 °C
mass: .0041 kg
specific heat capacity: 3.47 kJ/(kg*°C)

The energy transferred is:
mass x change in temperature x  specific heat capacity = (0.0041 kg)*(0.4 °C)*(3.47 kJ/(kg*°C)) = 0.0057 kJ

Our units of mass and temperature cancel appropriately, leaving units of energy kJ (kilojoules). 5.7 joules of energy are therefore transferred when rubbing your hands together.

To try to make sense of this quantity, let's convert it to energy in the form of dietary calories. 5.7 J = 0.00136 Cal (source). Given that your average apple contains 91 dietary calories (source), you could rub your hands together another 67,000 times (91/0.00136). This is assuming your body and digestive system are 100% efficient, which they aren't, but lets let the biophysicists deal with that.

Fun with Microwaves!

So microwaves rely on work, not heat to warm our meals. Heat was previously defined to be the flow of energy due to a difference in temperature, and I should add that this flow occurs spontaneously. This already seems to indicate that microwaving food does not involve heat- microwave pizza does not instantaneously become ready to eat. Additionally, heat relies on the notion of thermal equilibrium (two systems reaching the same temperature) to determine when energy is exchanged. Does your microwave reach the same temperature as the food you are heating? I hope not.

Microwave (ovens) use radiation to heat food. Electromagnetic radiation, to be more precise, whose waves fall in the "microwave" category in terms of frequency and wavelength. This radiation excites the atoms in your food, essentially making them jiggle and feel warmer to our tongues. I have implicitly related to temperature to jiggling of atoms, which is somewhat of an oversimplification but valid at this stage. This process can be considered work because it involves forces and displacement of atoms, albeit on an extremely tiny scale. Therefore, in accordance with out previous definition of work, microwave ovens use work to increase the internal energy of food.

If the aforementioned statements were entirely correct, then physics wouldn't be physics. Explanations always rely on particular perspectives on situations, whether microscopic, macroscopic, or otherwise. The increase of internal energy (like that caused by a microwave) is also due to another phenomenon that is actually the subject of this song:

I in no way own the aforementioned video or its contents. It is entirely the property of the band Muse.

Work and Internal Energy

Previously, the concept of heat was introduced and the First Law of Thermodynamics was represented mathematically. A more accurate version of this law is included in this post. The first law states that the internal energy of a system is equal to the sum of the heat input and the work done on a system (for the work a system does on its surroundings, simply change the sign of the W term in the equation for internal energy).

Work is defined in physics to be a force applied over a distance- in the case of thermodynamics, work is any transfer of energy that is not heat. This reasoning seems to be circular, but bear with the logic as these definitions in terms of one another have practical applications. Everyday examples that involve heat include:

-Adding milk to coffee
-ignition in a car engine (starting the car)

Examples of work:

- Microwaving a meal (NOT heat! More on this later...)
- Inflating a balloon

The First Law of Thermodynamics

Thermodynamics is a branch of physics that, as its etymology implies, deals with changes ("dynamics") in heat ("thermo"). The word "heat" has a different meaning in the language of physicists than they it does in ordinary, everyday language. Heat is the transfer of energy due to a difference in temperature, while colloquially it generally refers to a high temperature. This distinction will be elaborated upon in future posts, but for now heat (Q) can be related to other physical quantities such as internal energy (U) and work (W) by the First Law of Thermodynamics, represented mathematically in this post. In the next post the meaning behind these mathematics will be revealed.