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HEAT

Heat - An introduction:

The Universe is made up of matter and energy. Matter is made up of atoms and molecules (groupings of atoms) and 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. Many different types of energy can be converted into heat energy. Light, electrical, mechanical, chemical, nuclear, sound and thermal energy itself can each cause a substance to heat up by increasing the speed of its molecules. So, put energy into a system and it heats up, take energy away and it cools. For example, when we are cold, we can jump up and down to get warmer.

Heat can be a chemical or physical phenomena. All chemical phenomena ultimately reduce to physical phenomena (physics).


Video 1. How we sense hot and cold

Sensing Temperature

When something feels hot to you, the molecules in that something are moving very fast. When something feels cool to you, the molecules in that object aren’t moving quite so fast. Believe it or not, your body perceives how fast molecules are moving by how hot or cold something feels.

Your body has a variety of ways (senses) to detect energy.

  • Your eyes perceive certain frequencies of electromagnetic waves as light.
  • Your ears perceive certain frequencies of longitudinal waves as sound.
  • Your skin, mouth and tongue can perceive thermal energy as hot or cold.

What a magnificent energy sensing instrument you are!


Video 2. Changing states: matter!


Richard Feynman talks about fire


Appendix A

Changing State - Steve Spangler:

Student and Teacher worksheets

The following documents were created as part of the States of Matter Stage 3 project, incorporating heat:

  1. States of Matter Interview questions It has a simplified version of the interview questions used by Derek Muller in his youtube video States of Matter: https://youtu.be/KCL8zqjXbME
  2. Who's Hotter? Survey Who's hotter, boys or girls? Make your predictions then compare the temperatures of girls and boys. Were you right? Take the temperature of your metal handrail outside in the morning and afternoon. What do you think are the differences between metal handrails and boys' and girls' temperatures? Check your predictions against the results. Can you explain the findings?

Leslie's cube

Leslie's cube is a simple metal container (e.g. empty Milo tin) that with four differently painted sides/sections. If it is filled with hot water (at a safe temperature to avoid burns), you can use either your hands or a thermopile connected to a meter to try and decide which surfaces give out the most heat radiation.

Remember that as the water temperature the same throughout the container, all the sides of Leslie's cube are at the SAME TEMPERATURE but touch/measurement reveals that some surfaces give out more heat radiation than others.

These experiments should have proved that:

  1. Heat radiation travels through air
  2. It travels at the same speed as light
  3. Black surfaces are the best emitters of heat radiation
  4. Black surfaces are the best absorbers of heat radiation
  5. Shiny surfaces are the best reflectors of heat radiation
  6. Heat radiation can travel through a vacuum – that’s why we can feel heat from the Sun

Heat radiation is rays or waves of heat energy. In spite of what some people think, wearing clothes of different colours does not make a lot of difference to how well we can loose heat.

It is the layers of air between our bodies and the clothes that really matter.

For interior heating and cooling, the colour of a car is a lot less important than whether it is shiny or not.

Heat Problem:

The little light in the fridge was designed to shut off long before conservation of electricity was an accepted concern. Why?

All of the energy output from the light were it on would be generated within the refrigerator and the corresponding entropy would require extraction. A powerful bulb of say 20 Watts could substantially affect the cooling efficiency of the refrigerator.

Problem: How long will it take if we open the door to the refrigerator as a method to cool the house/room (provide adta such as relative temperature and volume.

This is a good one to know to save on your energy bills. Essentially, we are connecting the inside and outside of the device. We are extracting heat from the “inside” and dumping it into the “outside”. We can take a step back, though, and realize that every bit of power that runs the refrigerator must be dissipated somewhere. Therefore the net result is that the power running the device goes to warm the house, not cool it, though it certainly warms the house efficiently. Source: http://www.sparknotes.com/physics/thermodynamics/heat/problems.html


Heat - Misconceptions

Common Misconceptions about Heat and Insulation

The concepts of energy and heat are challenging for elementary students. Because young students are not ready to delve into kinetic theory and molecular motion, much of the explanation of heat and energy transfer is inaccessible to them. In addition, the use of the word “energy” in popular culture may interfere with the development of scientific understanding. Nevertheless, elementary students are capable of exploring heat through observations and qualitative, developmentally appropriate explanations. In fact, the idea that heat is transferred from one object to another via conduction is a grade-level expectation according to the National Science Education Standards (NRC 1996). During these initial explorations, teachers will encounter a variety of student misconceptions. Formative assessment and purposeful teaching will help prepare students to tackle more advanced concepts in the middle grades and beyond.

In this article, we’ve highlighted some common misconceptions about heat and insulation. Rather than provide an exhaustive list of all possible student ideas, we hope to give insight into ones that might be held by your elementary students. We’ve also provided tools for formative assessment and resources for teaching correct scientific concepts.

Heat Misconceptions Table

Students may think… Instead of thinking…
Heat is a substance. Heat is not energy. Heat is energy.
Temperature is a property of a particular material or object. (For example, students may believe that metal is naturally cooler than plastic.) Temperature is not a property of materials or objects. Objects exposed to the same ambient conditions will have the same temperature.
The temperature of an object depends on its size. Temperature does not depend on size.
Heat and cold are different. Cold is the absence of heat. Heat and cold can be thought of as opposite ends of a continuum.
Cold is transferred from one object to another. Heat is transferred from one object to another. Heat moves from the warmer object to the cooler object.
Objects that keep things warm (sweaters, mittens, blankets) are sources of heat. Objects keep things warm by trapping heat.
Some substances (flour, sugar, air) cannot heat up. All substances heat up, although some gain heat more easily than others.
Objects that readily become warm (conductors of heat) do not readily become cold. Conductors gain (and lose) heat easily.
Students may think… Instead of thinking…
Boiling is the maximum temperature a substance can reach. It is the maximum temperature of the liquid phase of the substance but not the gaseous one!
Boiling point of water is always 100oC They do not realise that the boiling point depends on air pressure and purity of the substance.
Steam can be 'seen' Steam is colourless - We see the condensing steam above a kettle spout - but below that it is colourless (Care steam burns are dangerous!
Heat always rises Warm particles tend to rise within a fluid because of density difference within the fluid…. but in conduction direction does not matter… and heat radiation is given out equally in all directions

Source: http://www.cyberphysics.co.uk/PGCE/Misconceptions/heat&temperature.htm

Seven Sins of Heat Transfer

True or false:

  1. Heat rises
  2. Particles of heat
  3. Expanding particles
  4. Shiny materials are good conductors
  5. Cold gets in
  6. Condensing and contracting are the same
  7. Trapped particles can’t move through a vacuum flask

Source: https://teachingofscience.wordpress.com/2014/05/13/heat-misconceptions/

Write a “True” or “False” by each statement about heat. - When I touch a cold rock with my warm hand, my hand will get warmer because heat travels from hot to cold.

  1. When I touch a cold ice cube with my warm hand, my hand will get colder because

heat travels from hot to cold.

  1. My gloves keep my hands warm because they produce heat.
  2. A cold snowball will give off cold air.
  3. A warm cup of hot chocolate will take heat from my cold hands.
  4. My hat keeps my head warm because it traps the heat from my head.

Other misconceptions/resources: 1. Infrared heater give off heat

No - InfraRed is NOT a kind of heat. In his book “ Clouds in a Glass of Beer,” Physicist C. Bohren points out that this “heat” misconception may have been started long ago, when early physicists believed in the existence of three separate types of radiation: heat radiation, light, and actinic radiation. Eventually they discovered that all three were actually the same stuff: light. “Heat radiation” and “actinic radiation” are simply invisible light of various frequencies. Today we say “UV light” rather than “actinic radiation.” Yet the obsolete term “heat radiation” still lingers.

Since human beings can only see certain frequencies of light, it's easy to see how this sort of confusion got started. Invisible light seems bizarre and mysterious when compared to visible light. But “invisibility” is caused by the human eye, and is not a property carried by the light.

If humans could see all the light in the infrared spectrum, we would say things like this: “of course the electric heater makes things hot at a distance, it is intensely bright, and bright light can heat up any surface which absorbs it.”

Question: A student takes a metal ruler and a wooden ruler from his pencil case. He notices that the metal one feels colder than the wooden one. Explain why.“

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teaching/stem/heat/home.txt · Last modified: 30/09/2018/ 11:47 (external edit)