Energy in Food
9SCIE - Energy for Life
Finn Le Sueur
2024
Energy
- Energy is measured in the scientific unit,
Joules
- As a shorthand we write Joules as
J
- It is named after James Joule, an English physicist
(1818-1889)
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Energy in Food
- Food contains chemical potential
energy, which is stored in the bonds between atoms and
molecules.
- When we eat the food, we break the bonds and get
energy!
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How much is a Joule?
- To lift this \(25g\) whiteboard marker 1m off the ground
takes \(0.245J\)
- For me (\(71kg\))
to jump \(0.3m\) into the air takes
\(208.8J\)!
- To warm \(1ml\) of
water by 1 degree C takes \(4.2J\)
Joules vs Calories
You may hear energy referred to by calories.
1 calorie (C) is equal to \(4.2J\),
or the amount of energy required to warm up \(1ml\) of water by degree C!
Ngohe: Your Lunch
Look in your bag for some food in a wrapper with a nutritional label.
How many Joules of energy does your snack contain? Make
a note of it in your book.
Hint: kJ means kilojoules or 1,000J. So 120kJ means
120,000J.
It takes you approximately \(147J\)
to do a starjump \(0.3m\) off the
ground. How many jumps do you have to do to burn off the energy from
your snack?
e.g. \(120,000/147=816\) jumps!
In fact, we can find the amount of energy in a food in the lab! We
will do this whakamātau later in this unit.
Before we start, recall that it takes \(1J\) to warm \(1ml\) of water by 1 degree C.
- Measure 10ml of water in a boiling tube
- Place that boiling tube in a clamp above a tripod
with gauze mat
- Light your food (peanut) on fire using the bunsen
burner
- Place the peanut on the gauze mat
- Record how much warmed the water gets!
