Missing arrow in concept map for balls pushing out water?

[maneesha]

In the final concept map for balls pushing out water, is there supposed to be an arrow from weight to water? This would indicate that both size (volume) and weight impact displacement of water. For example, a beach ball may displace less water than a bowling ball or even a baseball.

See https://carpentries.github.io/instructor-training/02-practice-learning.html#misconceptions

[brownsarahm]

This is tricky, any time the ball is more dense than water, then only the volume impacts the displacement(and the diagram is correct). The weight does not always impact the displacement. That said, the beachball is a good example of the fact that even the second model is not complete. We could fix by:

1. stating the different balls the child is experimenting with to start (to make it clear that it is only balls with density > water)
2. add text at the end noting this point, bringing the beachball into the discussion

Finding an example for this section was really hard but we do not need to be tied to this forever if others have a better example (that does not require significant prior domain knowledge of the trainees), or we can rework it a bit further.

[maneesha]

If we assume that the balls are denser than water, then yes, this works. So we could state that assumption as part of this model.

However, we do bring up density in the text in this section, when we refer to a "new understanding that incorporates the difference between properties of mass and volume." This implies that we are considering density.

[maneesha]

If we want to consider other examples that do not require significant prior domain knowledge of the trainees, I find it's generally useful to use examples that come from primary school education. Here are a couple of examples I have used of other broken mental models from a child's POV:

• I put a thermometer in a cup of hot coffee, and temperature goes up. I put a thermometer in a glass of ice water, and temperature goes down. Blankets are warm, so if I put a thermometer under a blanket it must go up! Then you learn that the blanket traps your body heat so if you put the thermometer under a blanket by itself, temperature will not go up.

• I see lightning and a few seconds later I hear thunder. I see and hear them at different times so they must be different events. Then you learn about the speed of light and speed of sound and that they are actually the same event.

[brownsarahm]

Thanks SO much!!

We also wanted this to use concept maps, so I have made a first draft at new ones for this

a child experiments with a thermometer ....

flowchart TD
    hc[fresh coffee] --> |put my hand in| flh[feel hot ] 
    hc --> | thermometer touches | thup[number goes <br> up a lot]
    ic[ice water] --> |put my hand in| flc[feel cold]
    ic --> |thermometer touches| thdn[number goes <br> down a lot]

this creates their initial mental model:

flowchart TD
    flhmm[feel hot ] --> |thermometer touches| thupmm[number goes <br> up a lot]
    flwmm[feel warm ] --> |thermometer touches| thupmml[number goes <br> up a little]
    flclmm[feel cool]--> |thermometer touches| thdnmml[number goes <br> down a little]
    flcmm[feel cold]--> |thermometer touches| thdnmm[number goes <br> down a lot]

and they extend it to

flowchart TD
     ble[blanket] --> |put over me| flwe[feel warm] 
    ble --> |thermometer touches| thupe[up a little]
  

but in reality

flowchart TD
    blc[blanket] --> |put over me| tr[traps warmth <br> from my body]
    tr -->  |feel air| flwc[feel warm] 
    blc --> |thermometer under with me| thupc[up a little]

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[ndporter]

Put out call for feedback on this issue in trainers Slack channel 2025-10-14.