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)

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!

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!

Kahoot Time!

https://create.kahoot.it/details/fast-food-guess-calories-1/3effdea3-1a35-4f0e-aa2d-ef18e3837d98

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.

1. Measure 10ml of water in a boiling tube
2. Place that boiling tube in a clamp above a tripod with gauze mat
3. Light your food (peanut) on fire using the bunsen burner
4. Place the peanut on the gauze mat
5. Record how much warmed the water gets!