An interactive model is not an experiment
Use a question about real water to help pupils explore what a model can explain and where they need more evidence.
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Imagine you’ve found a model for a lesson on changes of state. The particles move and the graph responds. You can picture the question you’ll ask the class. But what do you hope to hear back: a description of the screen, or an explanation of the science?
An animation can give you a way into that conversation. Running it produces observations of a programmed representation; it doesn’t measure what happens in real water. Helping pupils recognise that difference gives the discussion a purpose: deciding what the model helps them explain, and what they would still need to investigate.
Give the model a question worth exploring
Before opening the model, choose the relationship you want pupils to think about. In a lesson on changes of state, that might be the connection between energy transfer and temperature.
The moving particles and the curve then have a job. Pupils can use them to make a prediction, describe what they notice and explain how the two fit together.
This is part of scientific enquiry. The NGSS science and engineering practices guidance, a US framework, describes using models, recognising their assumptions and comparing predictions with the physical world.
You can make room for curiosity while keeping that comparison open. A model’s limitations give you something else to ask about.
Pause at 100°C
TopSchool’s own States of Matter Library activity offers a useful moment to explore. It represents water at normal atmospheric pressure. At 100°C, the number on the screen can stay the same while the model represents different processes.
Use Reset to leave the opening demonstration, then select 100°C and let the current temperature display settle. Changing the setting and watching the current display are two different things.
Try it yourself
At 100°C, compare Heat and Cool. What changes besides the temperature?
Start interactive model
Scroll across the model to reach every control, or expand it.
Open in Library for more space or if the model does not load here.
Pause there. Look at the transfer state alongside the temperature:
| What you notice | What it means here | What it cannot tell you |
|---|---|---|
| Liquid and gas at 100°C, with no net energy transfer | The model represents coexistence without net heating or cooling. | The setting alone does not establish active boiling. |
| Heat active, 100°C and a boiling label | Energy is being transferred during the modelled phase change. | The curve does not measure heat supplied to real water. |
| Cool active, 100°C and a condensation label | Energy is being removed during the modelled phase change. | Temperature alone does not identify the transfer direction. |
The temperature stays at 100°C in these situations, yet the transfer state differs. Invite pupils to explain which other clue on the screen matters. Give them a moment to put the difference into their own words. You can bring in the scientific vocabulary as you work through the explanation together.
OpenStax’s explanation of phase transitions connects a phase-change plateau with changes in intermolecular interactions while temperature remains constant. It also explains why boiling temperature depends on pressure. Keep that pressure condition with the 100°C example.
Keep the assumptions close to the explanation
A small phrase can make an explanation more careful. Saying “at normal atmospheric pressure” keeps the model’s 100°C boundary attached to its condition. The activity does not let you change pressure, so it cannot answer what would happen at another pressure.
The energy curve needs the same care. Its scale is relative: a segment does not give you heat in joules, and the animation’s duration cannot tell you the power of a real heater. The activity has no inputs for sample mass, measured heat supplied or apparatus calibration.
Read the particles as a representation too. Their on-screen size, spacing and speed are not measurements of real molecules. When water changes state, the explanation concerns interactions between molecules, rather than water molecules splitting apart.
These details help you keep the explanation connected to what the model can support. You can still explore the phase change while leaving questions about a particular sample open.
Take the question back to real water
Suppose you want to investigate whether a water sample’s temperature stays constant during boiling as energy is supplied. The model has given you a prediction. Now you need observations of the sample to compare with it.
That changes what you look for. Pressure, the measurement method and the recorded temperatures matter. A claim about energy transferred would need evidence for that quantity too; the relative scale on screen cannot supply it.
Ask whether the measurements are precise enough for the question and how uncertainty affects the conclusion. The connection between investigating and evaluating evidence also appears in England’s Key Stage 3 science programme. Choose an appropriate practical and explanation for your pupils’ knowledge of particles, temperature and graphs.
Keep this question alongside your review of the wider teaching material. The model’s role in the lesson matters as much as the way it looks.
Help pupils explain one boundary
Give pupils a little space to work out where their explanation stops. “The model is simplified” is a starting point. Ask them to name the simplification that affects the conclusion they want to make.
A short model-boundary card can hold that thinking. Here is one illustrative completion based on the 100°C heating state. It records screen behaviour, not an experiment with water.
- Prediction: With Heat active, the model will show boiling while its temperature display stays at 100°C during the phase-change plateau.
- Screen observation: Heat is active, the phase label says boiling and the current temperature display reads 100°C.
- Interpretation: In this representation, energy transfer during a phase change can occur without a temperature rise.
- Assumption or omission: The model assumes normal atmospheric pressure and uses a relative energy scale.
- Additional physical evidence needed: Temperature observations from a water sample during boiling, with pressure and the measurement method recorded, to assess that prediction for the sample.
Leave room for pupils to explain the last field in their own words. What would they need to observe, and how would it help them judge their prediction?
