4 Heat Energy Measurements
Click play on the following audio player to listen along as you read this section.
https://video.bccampus.ca/id/0_982zm8ys?width=608&height=50&playerId=23448552
Take a look at the picture of the fire to the left. If you were to describe that fire and you had the three words heat, temperature and energy to choose from, which would you say best describes the fire?
You might say that all three words could describe the fire and you would be right. As all three words can be used to describe a similar situation this could be confusing. As this chapter deals with heat energy you might have guessed that we are going look at this from the heat energy point of view. We’ll get to temperature in the next section but for now know that temperature is a measure of the intensity of the heat. We could describe the fire as very hot which would indicate a high intensity of heat.
At this point we should get a definition of energy. I’m going to refer to WIKIPEDIA here for the definition:
Energy: In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.
Thanks Wikipedia!
There are many forms of energy. We are just going to focus on heat energy in this section.
If you would like to know more about the different forms of energy check out the following link: Types of Energy (Solar Schools)
Measuring Heat Energy
In the last two sections we started off by going through the metric units and then the imperial units. Well there are only two units for each that we are going to deal with so we’ll introduce them all at once and then work through examples within metric and within imperial and then work between them. The four units we are going to deal with are as follows:
| Metric | Imperial |
|---|---|
| kilowatts (kW) | British thermal unit (btu) |
| calories (cal) | joules (J) |
Let’s take a look at the relationship between each of the units.
| Unit | Equivalent |
|---|---|
| kilowatt | 3412 btu’s 860,421 cal |
| British thermal unit | 0.293 kW 1055 J |
| calorie | 4.186 J |
| joules | 0.239 cal |
Note that there are a couple of equivalent numbers missing such as the number of kilowatts in a joule. These are not included as they are either too small or way large to bother with. The numbers above are generally the ones we need to know.
Something else to note is that often instead of using calories and joules we use kilocalories and kilojoules. A kilocalorie (kcal) is 1000 calories and it takes 1 kilocalorie to raise the temperature of 1 kilogram of water 1°C. As we learned before there are 1000 grams in one kilogram. Following the logic it would then take 1 calorie to raise 1 gram of water 1°C.
[latex]\begin{array}{rcl} \text{1 kilocalorie (1000 calories)} & \longrightarrow & \text{raises 1 kilogram (1000 grams) of water 1°C} \\ \text{1 calorie}& \longrightarrow & \text{raises 1 gram of water 1°C} \end{array}[/latex]
This same logic follows for the joule. One kilojoule eq