# Energy in Food

In this worksheet, students will learn about energy in food and the difference between scientific measurement of energy and the relevant terminology in everyday life.

Key stage:  KS 3

Curriculum topic:   Physics: Energy

Curriculum subtopic:   Calculation of Fuel Uses and Costs

Difficulty level:

### QUESTION 1 of 10

Energy is all around us: we use it, we make it and it is never created or destroyed, but changes forms.

We take in chemical energy from the food we eat; or actually, we use the food we eat to gain energy for us to use in a process called respiration. Energy in food is often measured in calories (cal), and you may know people that count how many calories they eat each day. In reality, the calories that people count are actually kilocalories (kcal). One kcal contains one thousand cal.  However, it is more correct to measure energy of any kind in standard units called Joules (J) and to convert calories into joules the number is multiplied by 4.2 (see below).  The amount of energy people need from food each day varies a lot according to age, lifestyle, pregnancy, general health, gender and other possible factors. For an adult, aproximately 8000-10 000KJ (or 2000-2200 calories) are the required daily energy intake.

This is a typical content label on a food package; it breaks down the product into its components, for example protein, carbohydrate and fat.  The energy ratings are also included, both in J/kJ and cal/kcal.

It is possible to determine the amount of energy in different types of food in a simple experiment. You need different types of food, e.g. crisps and bread, cut up in small pieces. You literally have to burn them under a boiling tube with a certain amount of water and measure how much the temperature rises. The more the temperature of the water increases, the more energy has been released from that type of food.

Be aware that this is an experiment that you may do at school, but you should not try it at home by yourself. The energy released by each food type is calculated using the following formula:

energy released from food per gram in Joules

 mass of water (g)  ×  temperature rise (ºC)  ×  4.2 = mass of food sample (g)

4.2 is a constant number (this means it never changes) and is related to the capacity of water to have its temperature raised.

You may have noticed that, although it was mentioned earlier that calories are used as a unit for energy in foods, in Physics energy is measured in joules (J).  Protein energy ranges from 2.44 kcal/g to 4.36 kcal/g. Fat has 8.37 kcal/g to 9.02 kcal/g and carbohydrates have 2.70 kcal/g to 4.16 kcal/g.

Now try this activity to see how you manage these energy calculations concerning food.

What type of energy is stored in food?

kinetic

heat

chemical

What process does our body use to make energy from food?

photosynthesis

respiration

What is the everyday term used to quantify energy in food?

calories

joules

In reality, is 'calories' the correct scientific term to measure energy in food?

yes

no

When people count the calories they eat every day, what are they actually measuring, if the term 'calories' is not scientifically correct?

What is the general daily intake of calories for a healthy adult?

500-1000

2000-2200

3000-3200

You are doing an experiment to measure energy in different types of food. What is it that you actually measure in order to determine the amount of energy?

mass of water

temperature rise

amount of fire

What is the typical unit for energy in physics? Type the whole word in the box below.

What is the energy content of protein in kcal per gram?

2.44 kcal/g to 4.36 kcal/g

8.37 kcal/g to 9.02 kcal/g

2.70 kcal/g to 4.16 kcal/g

What is the energy content of fat in kcal per gram?

2.44 kcal/g to 4.36 kcal/g

8.37 kcal/g to 9.02 kcal/g

2.70 kcal/g to 4.16 kcal/g

• Question 1

What type of energy is stored in food?

chemical
EDDIE SAYS
Energy stored in food is chemical.
• Question 2

What process does our body use to make energy from food?

respiration
EDDIE SAYS
Our body makes its own energy from food in a process called respiration.
• Question 3

What is the everyday term used to quantify energy in food?

calories
EDDIE SAYS
Energy in food is measured in calories in everyday life.
• Question 4

In reality, is 'calories' the correct scientific term to measure energy in food?

no
EDDIE SAYS
No, 'calories' is used to make things easier.
• Question 5

When people count the calories they eat every day, what are they actually measuring, if the term 'calories' is not scientifically correct?

kilocalories
kcal
EDDIE SAYS
Calories measured in food are actually kilocalories, to be scientifically correct. The abbreviation for kilocalories is kcal.
• Question 6

What is the general daily intake of calories for a healthy adult?

2000-2200
EDDIE SAYS
A healthy adult should generally consume 2000-2200 calories a day. However, this amount may vary according to age, gender, lifestyle and other factors.
• Question 7

You are doing an experiment to measure energy in different types of food. What is it that you actually measure in order to determine the amount of energy?

temperature rise
EDDIE SAYS
The temperature rise is measured every time you burn a different food sample.
• Question 8

What is the typical unit for energy in physics? Type the whole word in the box below.

joule
joules
EDDIE SAYS
In physics, energy is measured in joules (J).
• Question 9

What is the energy content of protein in kcal per gram?

2.44 kcal/g to 4.36 kcal/g
EDDIE SAYS
Protein energy content ranges from 2.44 kcal/g to 4.36 kcal/g.
• Question 10

What is the energy content of fat in kcal per gram?

8.37 kcal/g to 9.02 kcal/g
EDDIE SAYS
Fat energy content ranges from 8.37 kcal/g to 9.02 kcal/g.
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