Thermodynamics: Temperature

From Warmup Why was the test so hard?

You can do it! And you’ll learn a lot in the process!

Don’t get discouraged!

Also, we account for difficulty when we grade it.

Now you have a better idea what to expect next time.

What makes a good problem? (This is my question!)

Introductory questions: Apply a formula (simple HW problems)

You can answer simple questions without a deep understanding.

Nearly all of your sample problems on Monday were of the first type.

Don’t be satisfied by answering these questions!

Synthesis questions: How do the concepts allow me to solve new problems?

Swinging bucket problem is a synthesis problem. It is a good question because it shows me exactly what you don’t understand.

How to learn effectively?

How can you prepare to do these synthesis problems? Practice!

Working problems in class is not practice. (Well it would be for me….)

Even if you don’t work them out in detail, think deeply about the “extra problems” in the HW.

Don’t be satisified with just getting the right answer. Only you know if you really understood what you did!

From student ratings last semester:

Writing test questions was probably the best studying I had done for the class. Even if the question isn't used, writing a good question forces you to really know the concepts and how to apply them.

Challenge yourself!

From Warmup

I want to learn a little more clarification on expanding and contracting due to heat.

Several questions similar to this. We’ll discuss it today.

I was a little confused about the triple point of water. Is it one point or three? What exactly happens at the triple point of water? It talks about the equilibrium between ice, liquid water, and gaseous water, but wouldn't the gaseous water heat the ice?

It is a specific temperature and pressure at which ice, water, and water vapor exist simultaneously.

Why does America still not use the metric system?

The metric system is overrated. We should all use natural units: c = 1, G = 1, hbar = 1, kB = 1.

Did I per-chance leave my book in the classroom?

Anyone see an extra book somewhere?

Measuring Temperature

What is temperature? (Discuss with your neighbor)

How is temperature related to energy?

Do warmer objects (higher temperatures) always have more energy?

Does raising temperature always entail adding more energy?

Liquid Bulb Thermometer

Constant Volume Thermometer

From Warmup

At room temperature, the sphere can pass through the ring. After the sphere is heated, it cannot pass through the ring. Why? If the ring is warmed (instead of the sphere), can the sphere pass through? A: Yes, B: No Why?

Thermal Expansion

Two spheres are the same size and made of the same material, but one is solid and the other is hollow. Which expands more when the temperature is increased? Explain.

A) The hollow one expands more

B) The solid one expands more

C) They expand the same amount

D) It depends

From Warmup

They expand at the same rate because they have the same volume and are made of the same material. Thermal expansion is not dependant on mass.

Common Misconception:

The hollow one. Simple answer is that there is less mass to expand.

Why is this incorrect?

Thermal Expanssion

Bimetallic Strip

Why does this happen?

Shouldn’t it be like the ring – everything expands together?

Temperature

Is there a maximum temperature?

Is there a minimum temperature

How do you know

Shrinking balloon demo (air)

Ideal Gas Law

Equation of State Relates Pressure, Volume and Temperature What assumptions does this formula make?

From Warmup

To make a very sensitive glass thermometer, which liquid would be the best choice? Mercury, alcohol, gasoline, glycerin, water.

Gasoline. You want a large expansion coefficient so any small change in temperature is a large change in volume. This makes it easier to see. Gasoline has the largest of these materials as found in table 19.1 in the text.

Mercury would make the best choice because it has the widest range of temperatures while it is in its liquid state.