Energy Skate Park is a free PhET simulation in which a skater rolls up and down a track while live bar graphs and pie charts show their energy. It is the clearest way to make conservation of energy visible: students watch potential energy turn into kinetic energy and back, then add friction and see thermal energy appear.
This guide gives you a complete lab of about 50 minutes for middle and high school physics, a worked example with real numbers, and a free printable worksheet with a teacher answer key.
Free worksheet: 15 questions in five parts, data tables and an answer key with worked values. US Letter.
In this guide7 sections
Lab at a glance
| Grade level | 7–12 (physical science, physics) |
| Time | 45–60 minutes |
| Simulation | Energy Skate Park: Intro, Measure and Graphs screens |
| Key equations | PE = m × g × h and KE = ½ × m × v² |
| Students will | Describe energy changes on a track, explain the role of friction, measure and calculate energy, and show why mass does not change speed |
| Where to open it | Our science simulations page or the PhET website |
Know the simulation in 3 minutes
The simulation has four screens. This lab uses three of them:
- Intro: four tracks (Parabola, Ramp, Double Well, Loop), an energy bar graph, a pie chart, a speedometer and sliders for friction, gravity and mass. The default skater has a mass of 60 kg and gravity is 9.8 m/s².
- Measure: adds an energy sensor that shows the skater’s height, speed and each type of energy at any point on the track, plus a gravity setting for the Moon, Earth or Jupiter.
- Graphs: plots energy against position or time.
- Playground: lets students build their own tracks. It is great for an extension, but not needed here.
The colors stay the same everywhere: kinetic is green, potential is blue, thermal is red and total is purple. Tell students this at the start so they can read the graphs immediately.
Step-by-step lesson plan
Part A: Watch energy change (10 minutes)
On the Intro screen, students choose the Parabola track, turn on the bar graph and pie chart, and release the skater. They identify where potential energy and kinetic energy are greatest and sketch the bar graph at three points.
The key observation: the total energy bar never changes. Energy moves between potential and kinetic, but the total stays the same. That is conservation of energy, discovered rather than told.
Part B: Add friction (10 minutes)
Students slowly raise the friction slider. The skater no longer returns to the same height, and the red thermal energy bar grows with every pass. Ask: “Is energy being lost?” Students should see that the total stays the same; kinetic energy is being converted into thermal energy.
This is the most important conceptual moment in the lab, because “energy is lost to friction” is a common misconception. Energy is not lost; it changes into a form that is hard to use.
Part C: Measure and calculate (15 minutes)
On the Measure screen, students release the skater from rest, use the energy sensor at three points and record height, speed and energy. Then they check the sensor with the equations. Here is a worked example for a 60 kg skater released from rest 5 m above the bottom:
| Point | Height | Speed | Potential energy | Kinetic energy | Total |
|---|---|---|---|---|---|
| Start | 5.0 m | 0 m/s | 2,940 J | 0 J | 2,940 J |
| Middle | 2.5 m | 7.0 m/s | 1,470 J | 1,470 J | 2,940 J |
| Bottom | 0 m | 9.9 m/s | 0 J | 2,940 J | 2,940 J |
The prediction step is where the physics clicks. If all the potential energy becomes kinetic energy, then ½mv² = mgh, so v = √(2gh). For 5 m, that is √(98), or about 9.9 m/s, and the speedometer agrees.
Part D: Mass and gravity (10 minutes)
Students change the skater’s mass and release it from the same height. The energy values change, but the speed at the bottom does not. The equation from Part C explains why: mass appears on both sides and cancels.
Then they switch gravity from Earth to the Moon. The skater moves much more slowly, but without friction it still reaches the same height on the other side. It is a neat way to show that conservation of energy holds anywhere.
Part E: Graphs and loops (10 minutes, or homework)
On the Graphs screen, the energy-versus-position graph shows kinetic and potential energy as mirror images that always add up to a flat total line. Finally, on the Loop track, students search for the lowest start height that gets the skater all the way around. It must be higher than the top of the loop, because the skater still needs speed at the top to stay on the track.
Common misconceptions to watch for
- “Heavier skaters go faster.” The data says no: a heavier skater has more energy, but the same speed at the same height. This is the same idea as Galileo’s falling objects.
- “Energy is used up by friction.” The total energy bar stays the same; friction turns kinetic energy into thermal energy.
- “Potential energy is a fixed amount.” Potential energy depends on where you set the reference height. Move the reference line in the simulation and watch the values change while the motion stays the same.
- “Speed doubles if height doubles.” Speed depends on the square root of the height. To double the speed at the bottom, the skater needs four times the height.
Extension ideas
- Design challenge: in the Playground screen, students build a track with a jump and predict where the skater will land before testing.
- Roller coaster connection: students explain why the first hill of a real roller coaster is always the tallest, using conservation of energy and friction.
- Graph matching: show a graph of kinetic energy over time and ask students to sketch the track that produced it.
Review the lab later
A day after the lab, give students three questions from memory: where kinetic energy is greatest, what friction does to total energy, and why mass does not change speed. Recalling it later makes the lesson stick far better than rereading the worksheet. Our guide to active recall explains why. If your class also studied electricity this term, pair this lab with our Circuit Construction Kit lab guide, which uses the same worksheet format.
Frequently asked questions
What does Energy Skate Park teach?
It teaches kinetic energy, gravitational potential energy, thermal energy and conservation of energy. The Measure and Graphs screens add quantitative skills such as calculating energy and reading energy graphs.
Why does the skater not come back to the same height?
If friction is on, some kinetic energy is converted to thermal energy on each pass, so less energy is available to lift the skater back up. With friction set to zero, the skater returns to the same height every time.
What grade level is Energy Skate Park for?
The Intro screen works from about grade 6. The Measure and Graphs screens, with calculations, suit grades 8–12 and introductory physics.
