How Full is Choc-full? A delicious activity from Puzzles and Projects
Hungering for a maths activity you can really sink your teeth into? We’ve got a treat for you in this edited extract from Puzzles and Projects.
You’ll need an adult to help with this activity, but the delicious result is worth it!
Is a dish full of marshmallows really full? This yummy rocky road recipe shows that there’s still heaps of space in a ‘full’ dish.
Maths can always help you find a little extra room for dessert!
Safety: Ask an adult to supervise this activity. Use clean hands and equipment. Take care using the microwave and when cutting with the sharp knife.
You will need:
- Butter or spray oil
- 2 cups marshmallows
- 1 cup rice puffs
- 400 g dark chocolate buttons
- A small dish, about 2 cups in size
- Baking paper
- Metal spoon
- Large clean towel
- Metal spoon
- Microwave-safe glass or ceramic bowl
- Sharp knife
- Chopping board
What to do:
Step 1. Grease the small dish with butter or spray oil.
Step 2. Line the dish with baking paper.
Step 3. Put the marshmallows into the dish, so they reach the top. Is the dish really full?
Step 4. Pour the rice puffs into the dish. Shake the dish so they get into all the cracks. Is the dish really full?
Step 5. Place the dark chocolate buttons into a clean, dry microwave-safe glass or ceramic bowl.
Step 6. Use the microwave to heat the chocolate on medium for one minute.
Step 7. Carefully stir the chocolate with a clean, dry metal spoon.
Step 8. Repeat steps 6 and 7 until the chocolate is just melted and smooth. The bowl can get quite warm, so be careful when removing it from the microwave. Leave it to cool slightly if needed.
Step 9. Pour the chocolate into the dish. Gently stir the contents to let the chocolate fill all the gaps. Is the dish full now?
Step 10. Put the dish into the fridge and let it set for an hour.
Step 11. Turn the rocky road out onto the chopping board. Ask an adult to help you cut it into pieces using the knife. Enjoy!
In this activity, you’ve packed quite a lot into a small dish. Sometimes mathematicians and scientists need to know how tightly packed things are. The number they use to measure this is known as the packing density.
Packing density measures the proportion of the container that’s actually filled with stuff, rather than gaps. Solid rock has a packing density of 1, because it has no gaps. Lightly packed rice puffs might have a packing density of ½, meaning 1 cup would contain ½ cup of rice puffs, and ½ cup of air.
One way to increase packing density is to use a mixture of different-sized objects. The smaller rice puffs help fill the gaps between the bigger marshmallows. Of course, in this recipe, there’s still plenty of space for the chocolate!
Written by the team behind CSIRO’s Double Helix magazine, Puzzles and Projects is packed full of fun (and sometimes delicious) hands-on experiments, brainteasers, quizzes and comics. It offers hours of entertainment, sparked by the wonders of science, technology, engineering and maths (STEM).
The Double Helix team has a long-standing reputation for delivering expertly written, fascinating and fun science material for young people, with an aim to foster an interest in STEM.
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