This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!

You’ll discover how to boil water at room temperature, heat up ice to freeze it, make a fire water balloon, and build a real working steam boat as you learn about heat energy. You’ll also learn about thermal energy, heat capacity, and the laws of thermodynamics.

Materials:

• cup of ice water
• cup of room temperature water
• cup of hot water (not scalding or boiling!)
• tea light candle and lighter (with adult help)
• balloon (not inflated)
• syringe (without the needle)
• block of foam
• copper tubing (¼” diameter and 12” long)
• bathtub or sink
• scissors or razor
• fat marker (to be used to wrap things around, not for writing)

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Key Concepts

The terms hot, cold, warm etc. describe what physicists call thermal energy. Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy that object has.

There are three different scales for measuring temperature. Fahrenheit, Celsius and Kelvin. (There’s also a fourth temperature scale for absolute Fahrenheit called Rankine.) Temperature is basically a speedometer for molecules. The faster they are wiggling and jiggling, the higher the temperature and the higher the thermal energy that object has. Your skin, mouth and tongue are antennas which can sense thermal energy.

There are four states of matter: Solid, liquid, gas and plasma. Solids have strong, stiff bonds between molecules that hold the molecules in place. Liquids have loose, stringy bonds between molecules that hold molecules together but allow them some flexibility. Gasses have no bonds between the molecules. Plasma is similar to gas but the molecules are very highly energized. Materials can change from one state to another depending on the temperature and the bonds. Changing from a solid to a liquid is called melting. Changing from a liquid to a gas is called boiling, evaporating, or vaporizing. Changing from a gas to a liquid is called condensation. Changing from a liquid to a solid is called freezing. All materials have given points at which they change from state to state. Melting point is the temperature at which a material changes from solid to liquid.  Boiling point is the temperature at which a material changes from liquid to gas. Condensation point is the temperature at which a material changes from gas to liquid. Freezing point is the temperature at which a material changes from liquid to gas.

What’s Going On?

Heat is the movement of thermal energy from one object to another. Heat can only flow from an object of a higher temperature to an object of a lower temperature (this is the First Law of Thermodynamics). Heat is movement of thermal energy from one object to another. When an object absorbs heat it does not necessarily change temperature.  Objects release heat as they freeze and condense. Objects absorb heat as they evaporate and melt. Freezing points, melting points, boiling points and condensation points are the “speed limits” of the phases. Once the molecules reach that speed they must change state.

Heat capacity is how much heat an object can absorb before its temperature increases. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C. Heat capacity is influenced by the specific heat of the material and/or the amount of the material. Each material has its own specific heat. The higher a material’s specific heat is, the more heat it must absorb before its temperature increases. A larger amount of something will have a higher heat capacity then a smaller amount of something. Water has a very high heat capacity.

Questions:

1. True or False: Water is poor at absorbing heat energy.
2. True or False: A molecule that heats up will move faster.
3. True or False: A material will be less dense at lower temperatures.
4. For gases, if we increase the temperature, what happens to the pressure and the volume?
5. What is specific heat?
6. What is heat?
7. Does heat flow from cold to hot? Give an example.
8. What do the our body sense, heat flow or temperature? Are they the same thing?
9. How can we boil room temperature water without heating up the water?

Answers:

1. False.
2. True.
3. False. (Usually.)
4. If we increase the temperature, the pressure increases and the volume decreases. This is called the Ideal Gas Law (remember the ping pong balls from the teleclass?)
5. Specific heat is how much heat energy a mass of a material must absorb before it increases 1°C.
6. Heat is the movement of thermal energy from one object to another.
7. No. Heat flows from hot to cold. (This is the First Law of Thermodynamics.) A hot cup of coffee left out on a cold morning will eventually cool to the surrounding air temperature.
8. Heat flow. No they are not the same thing. Temperature is a measure of how much energy the molecules have.
9. By increasing the pressure by decreasing the volume, we can force the bubbles out of the water and it will boil. Boiling is when the liquid water turns into a gas, NOT when the liquid water heats up. Boiling can happen at many different temperatures when you change the pressure.

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