Heat Banner

HEAT EXPERIMENT#3

Start and end each session with a visible thinking learning task - what I used to think and what I think now - to help implement the Five Formative Assessment Strategies to improve student learning.

Why we focus on 'understanding the principles' rather than on 'learning the facts'

  • If your teaching/learning focuses on an understanding of the principles, you don't need to remember the facts - just look them up. No matter how many facts you remember, there is no guarantee that you will ever understand the principles that underly them.
  • All that you need to understand about the current scientific view about heat is….

“The beauty of a living thing is not the atoms that go into it, but the way those atoms are put together” 1)

Everything in the universe is made up of matter and energy.

  • Matter is made up of atoms and molecules (groupings of atoms).
  • Energy causes the atoms and molecules to always be in motion - either bumping into each other or vibrating back and forth.
    • The motion of atoms and molecules creates a form of energy called heat or thermal energy which is present in all matter. Even in the coldest voids of space, matter still has a very small but still measurable amount of heat energy.
    • Energy can take on many forms and can change from one form to another.

In summary, put energy into a system and it heats up, take energy away and it cools.

  • Heat can be a chemical or physical phenomena but all chemical phenomena ultimately reduce to physical phenomena (physics)
  • Thermal energy itself can cause a substance to heat up, simply by increasing the speed of its molecules. For example, when we are cold, we can jump up and down to get warmer. If we stop moving, we cool down. 2)

Video. Bill Nye - Heat (2min)


The five important concepts about heat & temperature

Heat Versus Temperature

  1. Temperature is the degree of hotness (average speed of all molecules)
  2. Heat is the quantity of hotness (total amount of heat energy for all molecules)
  3. Compare the speed (temperature) versus impact/energy (heat) of a table-tennis ball, tennis ball, basketball, cannon-ball - when each are traveling at exactly the same speed*

Video. Eureka - Heat Versus Temperature


Video - Heat transfer by conduction


More detailed information about the following videos can be found in the Teacher Workshops section of this WIKI:

AT THE END OF THIS SESSION YOU WILL BE GIVEN 10 MINUTES TO WRITE DOWN IN YOUR JOURNAL ABOUT ANYTHING THAT YOU HAVE CHANGED YOUR MIND ABOUT DURING THIS SESSION. WRITE DOWN WHAT YOU USED TO THINK AND WHAT YOU THINK NOW.

Conduction experiment


Video - Conduction experiment (conductivity of materials) (3min)

ENTER YOUR DATA HERE


Video: Bill Nye -Heat video for a rainy afternoon (22min)


Video - Eureka - Conduction (2min)


Radiation experiment:

When any type of light is absorbed by an object, that object will be heated. The infrared light from an electric heater feels hot for two reasons: 3)

A thermographic camera (also called an infrared camera or thermal imaging camera) is a device that forms an image using infrared radiation compared with a standard webcam/camera, which forms an image using visible light.

Ball Thermal Bounce Image

Figure 1. Thermographic Images - Show how a ball heats up after being bounced - Source: Caltech

You may think these infrared images of a boy holding a ball look unusual, but this is the way snakes normally see things!

Video 2. Eureka - Radiation & waves (4min)


Convection Experiment

Video 3. Eureka - Convection (5min)


Video: GCE Physics - Heat Transfer by Conduction (4min)


Video: Convection - Science Demonstration (3min)


Video - Fire, Heat, Light & Hot Air Rising (1.5min)

A QUESTION - Does 'heat rise' and/or 'does hot air rise'?

  1. 'Does hot air rise (due to heat)' or does 'cold air fall (due to gravity)'?
    • When you have two theories to explain the same thing, what can you do
    • To test a theory, design an experiment where each theory predicts a different outcome.
    • In the space station, there is plenty of air but almost no gravity.
    • If hot air rises, then it should also 'rise' in zero gravity. Does it?
    • Does hot air really rise?
    • High above our planet in the realm of satellites and space stations, the familiar rules of Earth do not apply. The midday sky is as black as night. There is no up and no down. Dropped objects do not fall, and hot air does not rise.4). In the absence of gravity, there is no buoyant force so no movement is possible physically but however hot air will start exchanging heat with the cooler air by means of conduction and radiation if they are in contact with each other and only by pure radiation if they are not in contact. ( no convection can takes place because of the absence of gravity) 5)


Video: Richard Feynman - What is fire? (4min)

Heat & Light In everyday conversation, when we say something is 'giving off heat' we are describing the emission of a specific part of the electromagnetic spectrum (namely the infrared spectrum). As you pour more and more energy into an object, the electrons get more and more excited (which is the process of absorbing photons), until they emit a photon of light when returning to a lower energy state. As an object gets hotter, the electrons can jump up further and further until when it eventually cools and returns to the ground state it emits visible (or UV/x-ray) light (photons). 6)

In thermodynamics, heat is a type of energy transfer in which energy flows from a warmer substance or object to a colder one. It can be defined as the total amount of transferred energy excluding any macroscopic work that was done and any transfer of part of the object itself. Transfer of energy as heat can occur through direct contact, through a barrier that is impermeable to matter (as in conduction), by radiation between separated bodies, by way of an intermediate fluid (as in convective circulation), or by a combination of these.[7][8][9] By contrast to work, heat involves the stochastic (random) motion of particles (such as atoms or molecules) that is equally distributed among all degrees of freedom, while work is confined to one or more specific degrees of freedom such as those of the center of mass.

Since heat (like work) is a quantity of energy being transferred between two bodies by certain processes, neither body “has” a definite amount of heat (much like a body in itself doesn't “have” work). In contrast, a body indeed has properties (state functions) such as temperature and internal energy. Energy exchanged as heat during a given process changes the (internal) energy of each body by equal and opposite amounts. The sign of the quantity of heat indicates the direction of the transfer, for example from system A to system B; negation indicates energy flowing in the opposite direction.

Although heat flows spontaneously from a hotter body to a cooler one, it is possible to construct a heat pump or refrigeration system that does work to increase the difference in temperature between two systems. In contrast, a heat engine reduces an existing temperature difference to do work on another system.

Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics.

Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called “natural convection”. All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means.

Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid). It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws.

Helio-centric versus Helical Motion Of Our Solar System (4min)

BEFORE END OF SESSION (allow 10 minutes)

Learning Tasks That Elicit Evidence of Learning 7)

At the end of this session, write down new answers to the same three questions you answered earlier:

  1. Are 'heat' and 'temperature' just different ways of saying the same thing?
  2. How does heat move from one object to another?
  3. How does heat move from the sun to the earth?

Have you changed your mind about any of the answers you gave at the beginning of the session?

References

1)
Carl Sagan - https://www.youtube.com/watch?v=XGK84Poeynk
2)
Jiggling molecules - http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/heat.html
3)
Amasci: http://amasci.com/miscon/miscon4.html#heat
4)
http://earthsky.org/science-wire/video-zero-gravity-coffee-cup
5)
https://physics.stackexchange.com/questions/262645/how-does-hot-air-act-in-zero-gravity
6)
Heat & Light - https://physics.stackexchange.com/questions/129363/how-can-heat-turn-into-light
7)
Dylan William - Formative assessment https://www.nwea.org/blog/2012/dylan-wiliam-the-5-formative-assessment-strategies-to-improve-student-learning/