1.2 Burning Candle as a System

This activity uses the burning of a candle to model a system. I've found it useful for a reminder to students to think about variable identification.

 Burning Candles as a System 

Student Task

A candle can be used as a simple model of a system. Each group have the same equipment and attempt to use the key vocabulary:

"Stores" "Equilibrium" "Energy" "Matter" "Flows" "Feedback" "Transfer" "Transformation" "Open System" "Closed System"

Apparatus

• Enamel dishes
• White tiles
• Jars that have straight edge.
• Paper
• Candles
• Matches
• Wooden Splints
• A systems approach!


Method / Procedure

  1. Carefully light the piece of paper whilst holding it over the enamel dish. Drop the paper into the dish before you burn your fingers.
  2. Observe the way in which the fire develops and then dies away.
  3. Light the candle observing how the flame develops. Drop some molten wax into the bottom of the dish so that you can stand the candle up on its own.
  4. Light a splint and then blow out the candle. Relight the candle bringing the splint towards the wick, watch carefully to see if it is necessary to touch the wick with the flame to relight it.
  5. Extinguish the candle and allow the wax to cool down completely. Relight the candle (is it necessary to touch the wick with the flame?) and observe very carefully the candle flame. Does it stay the same size, or does it get bigger or smaller or both? Does it reach an equilibrium?
  6. Discuss your observations with a systems approach

(i) Identify the stores
(ii) Identify the transfers and transformations involved
(iii) Inputs, outputs, flows
(iv) Equilibrium
(v) Feedbacks

  1. Use your observation and discussions to construct a graphical model (flow diagram) to describe the burning candle as a system. (Label the diagram fully with stores, transfer, transformation, processes and feedback).
  2. Use the model to make some predictions.

Approaches to Teaching

A candle can be used as a simple introductory lab to have students think about variable identification and how they might use a candle as a system. 

We approached this as a class activity with each group having the same equipment and the teacher guiding the groups through the steps, asking questions about their observations, eliciting the use of vocabulary appropriate to systems thinking.

"Stores" "Equilibrium" "Energy" "Matter" "Flows" "Feedback" "Transfer" "Transformation" "Open System" "Closed System"

The diagram at the end of the process was useful to point out that we don't use drawings just boxes and arrows and the differences between a system diagram with only inputs and outputs and a system diagram incorporating stores and flows. The role of the teacher in this activity is crucial, giving quick formative feedback.

To follow up, start the next lesson by asking students to discuss then feedback to you on the key terms that they remember or repeat the exercise of drawing a diagram if you have time.

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