Lesson 4: Energy

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What is energy? Why is it included in a chapter about matter? How are the two related?

Textbook Reading:  Chapter 3, part 2, pp. 66- 83



I. Energy

We use the word energy every day. We hear phrases like “energy crisis,” “running out of energy,” or “high energy bills.” Unfortunately, what we commonly mean by “energy” in these cases is some kind of fuel or other consumable resource.

In science, energy does not mean fuel. Instead, it is a more abstract concept:  “the capacity to do work.” It is not really anything concrete. It is not an object, but instead is a property that objects have.

Here’s what the famous physicist, Richard Feynman, had to say about energy:

There is a fact, or if you wish a law, governing all natural phenomena that are known to date. There is no exception to this law – it is exact so far as is known. The law is called the conservation of energy It says that there is a certain quantity, which we call energy, that does not change in the manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.

(Feynman, R. (1963).The Feynman Lectures on Physics. Book 1. New York: Addison-Wesley.)

What he is saying is that energy is a mathematical principle and no more. Isn’t that something to get your mind around?

A useful way to think about it is to think of various situations as “energy stores” rather than energy itself. These are situations with potential capacity to do work.

Some examples of energy stores:
1. Chemical (for example, alcohol + oxygen)

fireChemical energy stores can be used to move automobiles (internal combustion) and hot air balloons.

2. Kinetic (found in a moving object)


3. Gravitational (due to the position of an object in a gravitational field)

If you are sitting in a tree and drop a large rock, the gravitational energy will be transformed to kinetic energy. If your aim is good, you could drive in a stake with the dropped rock.

4. Elastic (for example, in a stretched rubber band or compressed spring)


5. Thermal (in a warm object)

coffee-heat-smallerThermal energy is important in determining the states of matter, as shown in this video (direct link).  Be sure to watch this one because the animations will help you visual the changes that occur between different states.


6. Magnetic (in magnets that are attracting or repelling )

johnny_automatic_magnet(Clipart from OpenClipArt)

Think of all the work a magnet can do.

7. Electrostatic (in two separated electric charges that are attracting, or repelling)


8.  Nuclear (released through radioactive decay, fission or fusion)

II. Introduction to Endothermic and Exothermic Reactions

As we study chemical reactions later in the course, we will find out that sometimes they release energy and sometimes they absorb energy. Our textbook is giving only a brief introduction in this chapter.

This video also gives an overview of endothermic and exothermic reactions (direct link).

III. Temperature versus Heat

Heat and temperature are further examples of vocabulary words with precise meanings in science that aren’t used as precisely in other contexts.

Temperature: A measure of a substance’s thermal energy (using a thermometer).

Heat: Thermal energy transfer or exchange between substances or objects.


Make sure you understand how to convert temperature units back and forth from Kelvin, Celsius and Fahrenheit, pp 71-73.

IV. Heat Capacity

We will be investigating heat capacity in lab this week, so pay particular attention to the terms heat capacity, specific heat capacity and the formula on page 75.

Maybe we’ll learn something that will help keep us cool.

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