Phases of Matter — Investigation · Physical Science: Matter, Forces & Energy, Grade 8
Explain solids, liquids, gases, and changes of state using particle motion and energy transfer.
Where does energy go while ice melts?
Investigate
How can energy enter a substance without a large temperature rise during melting?
Use three sessions: plan the question, boundary and predicted mechanism; collect safe records or analyze the supplied data; then graph, explain, compare with the initial model and propose a revision. The data option needs no special equipment. Time is a suggested allocation, not a measured completion claim.
Materials
- Ice, water, clear plastic cup, tray
- Thermometer designed for classroom use; timer
- Notebook; example data may be used without equipment
Before you begin
Use room-temperature surroundings only; no stove, hot plate, or boiling water is needed. Handle ice briefly and clean spills. Do not use a glass mercury thermometer.
Plan a controlled comparison
Observe change over time. Keep the cup, surroundings, thermometer position, and reading method consistent.
Method
- Make a notice-and-wonder record. State one observation, one possible explanation and a question the investigation can address. Agree on the measuring rule before seeing the results.
- Predict the temperature pattern while both ice and liquid water are present.
- Place ice and a little cold water in a cup on a tray. Measure the mixture every two minutes, stirring gently before reading. Keep the thermometer off the cup’s bottom.
- Record temperature and whether ice remains. Continue after the ice has melted if practical.
- Plot temperature against time. Mark the interval when solid and liquid coexist.
- Draw particle models before, during, and after melting. Explain what the model represents and what it leaves out.
- Revise the initial model, label the specific evidence that changed it and state a remaining question. Propose a changed condition, a predicted result and evidence that would challenge your mechanism.
Example data — for analysis when materials are unavailable
Illustrative example data for analysis, not measurements collected by the learner.
| Time (min) | Temperature (°C) | Ice present? |
|---|---|---|
| 0 | 0 | Yes |
| 2 | 0.5 | Yes |
| 4 | 0.5 | Yes |
| 6 | 1 | A little |
| 8 | 4 | No |
| 10 | 7 | No |
Analyze and explain
- Which interval has the smallest temperature change?
- Why does a near-flat interval not mean that no energy is entering?
- Why might classroom measurements differ from an ideal flat line at 0°C?
- Use a particle drawing to explain continued energy input during the near-steady temperature interval. Label solid and liquid fractions and the energy-transfer direction.
What a strong explanation includes
- Label graph axes and units.
- Use an interval and temperatures as evidence.
- Distinguish changes of state from increases in temperature.
- Identify the system, relevant variables and measurement method.
- Explain a model revision and a specific uncertainty.
Parent / teacher guide: discuss after the investigation
From 0–6 minutes the illustrative mixture stayed near 0°C while ice remained. Energy entering the mixture mainly changed the arrangement/interactions of particles during melting instead of increasing average kinetic energy greatly. After melting, temperature rose more. Sensor limits, impurities, and uneven mixing can affect readings. Use a particle drawing to explain continued energy input during the near-steady temperature interval. Label solid and liquid fractions and the energy-transfer direction. A complete report separates observation from inference. Preserve all planned trials, including a result that does not fit the prediction, and distinguish missing readings from zeros. The supplied numbers are illustrative, not records the learner collected. If observations differ, check the method, units and conditions before deciding which claim is supported. A schematic model should connect parts through a mechanism and explicitly name its limits. Describe a follow-up that changes one intended condition, keeps influential others comparable, and states the possible result that would challenge the explanation. A proposed improvement is not confirmed until it is retested. Different defensible conclusions can receive credit when they use the actual evidence and meet the stated criteria.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.