Investigation 8 — Calories and Watts: Understanding
Units of Energy and Power
Objectives:
In this investigation, students will increase their energy literacy by learning
about specific units of energy, such as
calories, and units of power, such as
watts and kilowatt hours. The handson tasks and physical activities that
make up these lessons are intended to
make learning about these important
scientific concepts fun and engaging.
Key questions:
•What is a calorie and how is it used
to measure the amount of energy in
food?
•What is a watt and how is it used to
measure the rate of energy transfer?
•What is a kilowatt hour and how are
these units related to electricity bills?
Time required:
This moderate investigation will
require several hour-long lessons,
including time for students to conduct
an energy audit.
Introduction:
This investigation will begin with a focus on the energy in food. Begin
a conversation about why humans need to eat. Ask students whether all
food contains the same amount of energy. Ask students if they know how
much energy is in a specific food item, like an apple. Lead the discussion to
explain that a unit, called a calorie, is used to measure the amount of energy
in food. Go even deeper by explaining how a calorie is based on the amount
of energy required to raise the temperature of one kilogram of water by one
degree Celsius and that other units such as joules and kilojoules are also
used as units of energy.
At this point, divide the class in groups and ask each to list their favourite
foods. Hand out chart paper and demonstrate how to create a T-chart using
food and calories in the two columns. Give students time to research the
number of calories in each of the food items. As a final task, use Health
Canada’s website for students to discover how many calories they require
each day based on three different activity levels (hc-sc.gc.ca/fn-an/foodguide-aliment/basics-base/1_1_1-eng.php).
Development:
Recommended grades:
3-6
Canadian National Standards for
Geography:
Geographic Skill 3: Organizing geographic information
•Prepare maps to display geographic
information.
•Construct graphs, tables and
diagrams to display geographic
information.
Geographic Skill 4: Analyzing geographic information
•Use simple mathematics to analyze
geographic data.
Next, remind students that all living things need energy to survive. Ask
them to draw comparisons to electronic devices. Begin a discussion about
how the energy in food differs from the electricity required to power
electronics. Discuss the concept of a watt and compare that to a calorie.
Similar to the T-chart from the previous step, brainstorm a list of devices
that use electricity and ask students to find out how many watts they
require. Next, introduce the concept of a classroom energy audit and
explain how a spreadsheet or a table is a great way to create and organize
a list of all the electrical devices and lighting in the classroom. Include the
wattage of each device in the table, and assign groups of students to track
specific devices. Brainstorm and discuss effective strategies for measuring
the number of minutes/hours their device is used each day. Make sure
to track electricity use over at least three school days in order to generate
averages and to increase accuracy.
.../continued
Energy Resources
Investigation 8 — Calories and Watts: Understanding
Units of Energy and Power
Geographic Skill 5: Answering geographic questions
•Use methods of geographic inquiry
to acquire geographic information,
draw conclusions and make generalizations.
Background:
These activities are more suitable for
younger students who are developing a
basic understanding of units of energy.
However, portions of this investigation
would be useful for older students to
review. The concluding activity can be
incorporated into physical education
or any time throughout the day when
you want students to be active. Older
students can explore more complex
concepts such as the volume of coal
or natural gas required to produce a
kilowatt or a megawatt of power.
After completing the audit, explain to students that utility companies
charge for electricity with a unit of energy called a kilowatt hour (kWh).
Each kWh is equivalent to 1,000 watts being used for one hour. Depending
on the age of your students, have them calculate the total number of
kilowatts used during the classroom audit and divide by the number of days
in your audit to get daily averages. Calculate how much this would have cost
based on electricity rates in your location.
Conclusion:
Conclude this activity by calculating the distance you would need to walk
or run to use the equivalent number of calories for some of the students’
favourite foods. Assuming a 40-kilogram child uses about 150 calories to
walk for an hour at four kilometres per hour, a 600-calorie cheeseburger
would take four hours or 16 kilometres to burn. Using a tool like Google
Earth, students can measure and create a short circuit around your school.
Challenge your class to run or walk this distance.
Extensions:
Extend these concepts further by having students perform home energy
audits, and keep track of the time they spend on electronic devices. Have
students develop a plan for reducing the amount of electricity wasted at
school and at home by stressing the importance of conservation. You can
also sign up your class for the 2015 Classroom Energy Diet Challenge
(energydiet.canadiangeographic.ca).
Additional resources:
What is a calorie?
hc-sc.gc.ca/fn-an/food-guide-aliment/basics-base/1_1_1-eng.php
kids.saveonenergy.ca/en/what-is-electricity/index.html
hydroone.com/Pages/Default.aspx
Energy Resources