We hear calorie; we think food. But is that justified? Are calories only used to indicate how much energy can be accredited to a certain food product or are calories also useful in other ways? And maybe a question that is even more important, what exactly is a calorie?
Definition: A calorie is the amount of energy that we need to raise the temperature of one gram of water by one degree Celsius, at a pressure of one atmosphere.Ebbing, D. and Gammon, S. (2011). General chemistry. Australia: Brooks/Cole Cengage Learning.
All these units we use to measure a calorie can seem pretty dry. So imagine boiling water to make some tea. You are standing in your kitchen so we can assume that the pressure you are working with is one atmosphere. Underneath your kettle, you have a heat source that will slowly raise the temperature of the water you are trying to heat up.
The heat is a type of energy (thermal energy) that can be transferred to the kettle. The fire is much warmer than the kettle is but the part of the kettle closest to the heat source, will warm up by absorbing energy from the fire. As you know from putting a kettle of water on the stove and turning it on, after a while both your kettle and the water in it will get warm. The energy that is being transferred from the heat source to the kettle is changing the temperature of the water.Schobert, H. (2013). Energy. Routledge.
Using a calorie to express a measure of energy can be useful at times. Many chemists, nutritionist, food scientists and now and then physicists will have to use a calorie to take a closer look at what is going on on an energy level while getting to the bottom of a problem. Before it is useful, however, knowing you can express a calorie in joule is important. One calorie is equal to about 1.184 joules, and 1 joule can be expressed as N·m or m2·kg·s-2 . Most often the calorie will not be used for calculations unrelated to food, and instead, the joule is used.Thompson, A. and Taylor, B. (2008). Guide for the use of the International System of Units (SI). Gaithersburg, M.D.: National Institute of Standards and Technology.
Using calories to express the amount of energy you are talking about does not change what you are talking about. You can tell someone how much you weight in for instance kilograms but also in pounds, and it will not change your weight. You can also tell them how tall you are in centimetres instead of in inches, and you will not suddenly be taller by doing so. You just change the way of expressing how much you weigh or how tall you are.
When eating food, we supply our bodies with energy. The amount of energy we get from food is expressed in calories. If we eat a lot and take in more energy than we use, our bodies will store that energy in the shape of fat. And when we need to stay warm, move or do other things, we use the directly available energy from food or the energy we have stored.McCall, Richard Powell. Physics Of The Human Body. Baltimore, Md.: Johns Hopkins University Press, 2010. Print.Haugen, David M, and Susan Musser. Nutrition. Detroit: Greenhaven Press/Gale Cengage Learning, 2012. Print.
Calorie (cal) or KiloCalorie (kcal)?
A calorie is often used interchangeably with a kilocalorie. There is a difference between a calorie (cal) and a kilocalorie (kcal) however. A kilocalorie (like the name suggests) is the amount of energy that is needed to raise the temperature of one KILOgram of water by one degree at a pressure of one atmosphere. This means that in one kcal, you can find 1000 regular calories.
When we talk about food and calories, you often read amounts like; 230 calories per serving. And this is where it gets confusing. When we talk about food, we say 230 calories, when we are talking about kilocalories. We need more than 230 single calories per serving! So when defining the calories on food labels or in your food, realise that you are dealing with a unit that describes the amount of energy that is needed to raise the temperature of one KILOgram of water by one degree under standard circumstances.Haugen, David M, and Susan Musser. Nutrition. Detroit: Greenhaven Press/Gale Cengage Learning, 2012. Print.
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|1.||↑||Ebbing, D. and Gammon, S. (2011). General chemistry. Australia: Brooks/Cole Cengage Learning.|
|2.||↑||This work is copyrighted by the mentioned creator. The license under which this work may be used can be found at http://creativecommons.org/licenses/by/4.0/. For more information on the creator and media, please visit: https://www.flickr.com/photos/felipevalduga/|
|3.||↑||Schobert, H. (2013). Energy. Routledge.|
|4.||↑||Thompson, A. and Taylor, B. (2008). Guide for the use of the International System of Units (SI). Gaithersburg, M.D.: National Institute of Standards and Technology.|
|5.||↑||McCall, Richard Powell. Physics Of The Human Body. Baltimore, Md.: Johns Hopkins University Press, 2010. Print.|
|6, 7.||↑||Haugen, David M, and Susan Musser. Nutrition. Detroit: Greenhaven Press/Gale Cengage Learning, 2012. Print.|