The free PhET Energy Forms and Changes simulation from the University of Colorado Boulder lets students watch energy move: from a burner into a block of iron, from falling water into a generator, from sunlight into a light bulb. This PhET Energy Forms and Changes lab turns that playground into a structured 50-minute lesson on heat transfer, energy systems and conservation of energy.
It fits physical science, physics and integrated science courses in grades 6–10 and needs nothing but a browser. If you are planning a simulation-heavy unit, the classroom simulations hub lists every PhET lab guide on this site, including the Energy Skate Park worksheet, which pairs well with this one.
In this guide10 sections
Learning goals
- Describe how thermal energy moves from warmer objects to cooler objects until they reach the same temperature.
- Compare how quickly different materials (iron, brick, water, olive oil) change temperature.
- Build an energy system with a source, a converter and a user, and trace each energy transformation.
- Explain why the total amount of energy stays the same even when some of it ends up as “wasted” thermal energy.
Before class
Open the simulation on the PhET website (search “PhET Energy Forms and Changes”) and test it on student devices. The HTML5 version has two screens: Intro, with blocks, beakers, burners and thermometers, and Systems, where students connect an energy source to a converter and a user. Turn on the Energy Symbols option once yourself so you can show students what the small energy “chunks” represent. Screen layouts can change between versions, so do a quick preview the day before.
Students work best in pairs: one person controls the simulation, the other records data, and they swap roles halfway. A quick reminder of group work roles keeps the recorder from becoming a spectator.
Part 1: Heating and cooling (Intro screen, about 20 minutes)
Step 1 – Make a prediction
Ask: “If we put an iron block and a brick on two identical burners for the same time, which one gets hotter faster?” Students write a prediction and one reason before touching the simulation.
Step 2 – Test it
- Place the iron block on one burner and the brick on the other.
- Attach a thermometer to each object.
- Push both heaters to full heat at the same moment and watch for about 15 seconds.
- Record which object’s thermometer rises faster, then turn the heaters off and observe what happens.
Step 3 – Liquids
Repeat with the beaker of water and the beaker of olive oil. Students should notice that the water warms more slowly. Introduce the idea that some materials need more energy to change temperature (specific heat capacity) without requiring the formula yet.
Step 4 – Contact between objects
Heat the iron block, then place it in the beaker of water. Turn on Energy Symbols and ask students to describe which direction the energy chunks move and when they stop moving. This is the moment to name thermal equilibrium.
Data table
Have students copy this table into their notebooks or a shared document.
| Trial | Objects compared | Prediction | Which warmed faster? | What happened when heat was turned off? |
|---|---|---|---|---|
| 1 | Iron vs. brick | |||
| 2 | Water vs. olive oil | |||
| 3 | Hot iron placed in water | Direction of energy flow: | Final temperatures: | |
| 4 | System you built (Part 2) | Energy chain: | Where was energy “lost”? |
Part 2: Energy systems (Systems screen, about 20 minutes)
On the Systems screen, students choose one item from each column: a source (such as the faucet, the sun, the tea kettle or the cyclist), a converter (a generator or a solar panel) and a user (such as a light bulb or a beaker of water).
- Build three systems. For each, write the energy chain in words, for example: mechanical → electrical → light + thermal.
- Compare light bulbs. Run the same system with the incandescent and the fluorescent bulb. With Energy Symbols on, students count roughly how many chunks leave each bulb as light versus heat.
- Change the input. Reduce the sunlight with clouds or slow the water flow and record what changes at the user end.
- Stop feeding the cyclist. Students observe what happens to the system when the cyclist runs out of energy, which leads naturally to a conversation about food as chemical energy.
Discussion questions
- Why did the iron block heat up faster than the brick on the same burner?
- When the hot iron block went into the water, why did the energy stop flowing after a while?
- Which bulb was more efficient, and what evidence from the simulation supports your answer?
- In your favorite system, where did energy end up that was not useful? Did that energy disappear?
- Name a real device at home that follows the same energy chain as one of your systems.
Answer guide for teachers
Iron warms faster than brick and olive oil warms faster than water because those materials need less energy per degree of temperature change. Energy flows from the hot block into the cooler water until both reach the same temperature, so the flow stops at equilibrium. The fluorescent bulb converts a larger share of its incoming energy into light, while the incandescent bulb releases more thermal energy, so the fluorescent bulb is more efficient. In every system the total energy is conserved; the “lost” energy is still present as thermal energy spread into the surroundings.
Differentiation and extensions
- Support: give a word bank (thermal, mechanical, electrical, light, chemical, radiant) and a partially completed energy chain.
- Challenge: ask students to design the most efficient system possible and justify their choice using energy-chunk counts.
- Connect to math: older students can calculate efficiency as useful output ÷ total input × 100 using their estimated chunk counts.
- Close the lesson: use one of these exit ticket ideas, such as “Draw one energy chain you built and circle the wasted energy.”
Frequently asked questions
Is the PhET Energy Forms and Changes simulation free?
Yes. PhET simulations are free to use in the browser, and teachers can create a free PhET account to access additional teacher-submitted activities.
What grade level is this lab best for?
The Intro screen works well from about grade 6, while the Systems screen and efficiency extension suit grades 8–10 physical science and introductory physics.
How long does the lab take?
Plan for one 45–55 minute period: 5 minutes for predictions, 20 minutes per screen and a short discussion. You can split it over two days if you add the efficiency calculations.
Does it work on Chromebooks and tablets?
The HTML5 version runs in modern browsers, including on Chromebooks and tablets. Test it on your school’s devices before class, since network filters sometimes block new sites.
Wrapping up
Energy is abstract until students can watch it move, and this simulation makes the invisible visible. Run the heating trials first, let students build their own systems second and finish with the conservation question: if energy is never destroyed, where did it go? For a related follow-up, try the States of Matter simulation lab, which connects thermal energy to particle motion.
