Demonstration Class:Science is Real,

Science is Creative

Johnny B. Holmes, Ph.D.

Professor of Physics

Questions and Answers

To understand things, good answers are, of course, important. (But nobody is going to pay you a lot just to be a Dr. Google!)

Just as important as answers is asking good questions! Not just what we know, but how do we know that, where did that answer come from, is that the best answer, what are the consequences of this answer, etc.

In this demonstration lecture, I’ll be posing a lot of questions. Feel free to answer those questions out loud or quietly to yourself.(no need to raise your hand)

Feel free to ask your own questions!

BACKGROUND:What is Science?

Not every field or subject is a science (otherwise why use the term science).

Is Biology a science?

Is English Literature a science?

Is Psychology a science

What are the essential features of science?

What is Science?

Anything that follows the scientific method can be considered a science:

1. Define what you are studying.2. Observe (take data – must be repeatable).

3. Hypothesize (make sense of the observations, that is, abstract basic principles) This should suggest new things to look for. If it doesn’t, it is not a good hypothesis.

4. Test (basically repeat step 2)

Biology and Physics: Two Cultures

“In general, physicists stress reasoning from a few fundamental principles – usually mathematically formulated – and seek to build understanding from the simplest possible models.  They view the world quantitatively and pay much attention to constraints, such as conservation laws, that hold regardless of a system’s internal details.

From article by Dawn Meredith and Edward Redish in Physics Today, July 2013 issue, page 39. 

Biology and Physics: Two Cultures

Biologists, on the other hand, focus on real examples and emphasize structure–function relationships; they rarely stress quantitative reasoning.  The systems they deal with are almost always highly complex, with many interacting parts that lead to emergent phenomena.  Biologists recognize that their discipline is subject to the historical constraint that natural selection can only act on pre-existing molecules, cells, and organisms, so their reasoning often depends more strongly on what exists than on ‘fundamental’ abstract principles or simplified pictures.”

From article by Dawn Meredith and Edward Redish in Physics Today, July 2013 issue, page 39.

Need for Physics in the Life Sciences

“… The life sciences have grown explosively as new techniques, new instruments, and a growing understanding of biological mechanisms have enabled biologists to better understand the physiochemical processes of life at all scales, from the molecular to the ecological.  Quantitative measurements and modeling are emerging as key biological tools. …”

From article by Dawn Meredith and Edward Redish in Physics Today, July 2013 issue, page 38.

EXAMPLE OF A SITUATION:Warm blooded versus Cold blooded

Biology

We are warm blooded, snakes and lizards are cold blooded.

What are the advantages and disadvantages of the two?

How do we regulate our heat (regulate our temperature)?

Warm blooded vs. Cold bloodedBiology

Warm blooded:advantage: quicker response times in cool weather;

disadvantage: requires more food to maintain the warm temperature.

What limits how hot we can operate at?Why is a fever dangerous?

Warm blooded vs. Cold bloodedChemistry

What limits how hot we can operate at?Why is a fever dangerous?

In chemistry you will learn that certain proteins will “unravel” at certain temperatures. This disrupts the biochemical processes.

So how do we regulate our temperature?

Warm blooded vs. cold bloodedPhysics - Regulate Temperature

First, what is temperature? (This is where the physics comes in.) What exactly does temperature measure?

To get some idea of what temperature is, how do we actually measure temperature?

How does the thermometer work?Are there different kinds of thermometers?Can we measure the surface temperature of the sun, or the temperature of a hot furnace, or the temperature of (cold) space?

Temperature and Energy

There have been various theories of what heat is. Some hypothesized that heat was a substance. The current theory is that heat is a form of energy. Looking down at the molecular level, we can theorize that the heat energy is actually the kinetic energy of the molecules.

[In physics, energy has a very strict definition: energy is the capacity to exert a force through a distance.

Kinetic energy is the energy of motion and depends on both the mass and speed of the object.]

Temperature and Energy

Therefore, if we measure the temperature, we have some idea of the amount of energy in the object.

To warm something up, we need to add energy. To cool, we need to take energy (heat) away.

We eat food, which has chemical energy (measured usually in calories) that we “burn” to turn into energy for our muscles but some is turned into heat energy (kinetic energy of the molecules).

Because we are always generating heat, we must always get rid of heat – but in a way that the two balance so as to maintain a constant temperature.

Energy, Power, and Cooling

Because we need to get rid of heat, we have a process that moves heat energy per time. In physics, we define POWER as the change in energy per time (usually measured in Watts, but sometimes in horsepower).

Because cooling is a flow of energy, we can use the concept of power to describe this.

Cooling power

How does our body control its temperature?How do we help our body control its

temperature?By what methods do we lose heat?What affects the amount of heat loss, i.e.,

cooling power, in each method? In other words, can we find a relation between heat loss (power) and the different parameters of the situation?

Cooling/heating power

Are these same methods that are used in cooling our bodies also used in cooling our houses, or keeping them from cooling too fast in the winter?

What is the difference between cooling and heating?

Are these same methods that are used for cooling also used for heating our houses and our food?

Methods of moving heat

• Convection (heat carried by material)

• Conduction (heat that goes through a material)

• Radiation (heat that goes through space, whether empty or not)

• Evaporation (heat necessary to pull molecules out of a liquid and free them to be a gas; melting is the heat necessary to break molecules apart so that they can move more freely as a liquid)

1. Convection

Amount of heat moved per time depends on a) how much energy the material can carry (per gram, per mole, or per molecule’ and per temperature unit) called its heat capacity

b) how much material is heated c) how fast the material is moved d) how hot the material is (its temperature)

relative to where the heat energy is goingExamples: convection ovens, gas furnaces, blood

flow

2. Conduction

Amount of heat moved depends on

a) how easily the energy moves through the material (its thermal conductivity)

b) the temperature difference between the ends

c) the area that the heat moves across

d) the distance that the heat has to move through

Example: heating a pan of water, wearing gloves in cold weather

3. Radiation

Amount of heat transmitted depends on

a) how hot (the temperature) of the emitting object

b) how big (surface area) of the emitting object

c) how cool (the temperature) of the surrounding space or objects are

Examples: microwave ovens, the sun

4. Evaporation

Amount of heat transmitted depends on amount of energy required to “unbind” the molecules from nearby molecules in the liquid state (called latent heat of vaporization), and the number of molecules (amount of material) that are so “liberated”.

Example: sweat

Question: would it have been better to use alcohol as a cooling liquid instead of water in humans?