Physics · 12th Grade

Active learning ideas

Conservation of Energy: Non-Conservative Forces

Students often struggle to accept that energy isn't always conserved within a system when non-conservative forces are present, so active learning is essential. Hands-on experiments and collaborative analysis help them see that energy transforms rather than vanishes, building conceptual permanence beyond abstract equations.

• Common Core State Standards
• HS-PS3-3

• 25–55 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Inquiry Circle
• 55 min · Small Groups

Inquiry Circle: The Friction Energy Budget

Groups release a block from a measured height down an inclined ramp and measure its speed at the bottom using a photogate. Students calculate expected speed from energy conservation, identify the discrepancy, and use temperature probes on the surface to estimate thermal energy generated. Groups reconcile their energy budgets.

Explain how non-conservative forces alter the total mechanical energy of a system.

Facilitation Tip

During Collaborative Investigation: The Friction Energy Budget, ensure each group records temperature changes and displacement measurements simultaneously to connect friction’s work with thermal energy output.

What to look for

Present students with a scenario: a block slides down a ramp with friction. Ask them to write the energy conservation equation that includes the work done by friction. Then, have them identify which terms represent initial mechanical energy, final mechanical energy, and the work done by friction.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Think-Pair-Share
• 25 min · Pairs

Think-Pair-Share: The Ski Jump Problem

Present a skier going down a slope with a given friction coefficient and ask students to predict landing distance on a flat run-out. Pairs first estimate using perfect conservation, then revise with friction, comparing results. Whole-class discussion highlights how friction coefficient changes outcome non-linearly.

Analyze the role of friction in converting mechanical energy into thermal energy.

Facilitation Tip

When running Think-Pair-Share: The Ski Jump Problem, ask students to sketch energy bar charts before and after the jump to make the energy loss tangible.

What to look for

Pose the question: 'If a ball is dropped and bounces, but each bounce is lower than the last, where is the mechanical energy going?' Facilitate a small-group discussion where students explain the role of air resistance and the transformation into thermal energy.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 03

• Jigsaw
• 50 min · Small Groups

Jigsaw: Real-World Friction Scenarios

Expert groups each research one application (car braking systems, conveyor belts, bicycle gears, turbine bearings) using a structured worksheet. Groups reassemble and teach each other how friction affects energy efficiency in their assigned system, then collaboratively rank systems by energy waste.

Predict the final velocity of an object sliding down a ramp with friction, using energy principles.

Facilitation Tip

In Jigsaw: Real-World Friction Scenarios, assign each expert group a different friction context so they can compare how direction and magnitude affect mechanical energy.

What to look for

Provide students with a diagram of a car braking. Ask them to list at least two non-conservative forces acting on the car and explain how these forces affect the car's mechanical energy, specifically mentioning the conversion to thermal energy.

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

A few notes on teaching this unit

Teach this topic by starting with physical experiences, not equations, so students feel energy conversion before they formalize it. Avoid overemphasizing friction as always opposing motion; instead, use examples where friction drives motion, like conveyor belts, to build nuance. Research shows that when students manipulate variables in real time, their misconceptions about energy ‘loss’ diminish faster than with passive demonstrations.

Students will trace energy flow through real-world systems, correctly accounting for mechanical energy loss due to non-conservative forces. They will justify their reasoning using the modified energy equation and explain energy transformations verbally and in writing.

---

Watch Out for These Misconceptions

• During Collaborative Investigation: The Friction Energy Budget, watch for students who assume friction always slows objects down.

  Use the conveyor belt model in the lab: students place a book on a moving belt and measure its acceleration. Ask them to draw the friction force vector to show how friction can increase kinetic energy when aligned with motion.

• During Jigsaw: Real-World Friction Scenarios, watch for students who say energy ‘disappears’ when friction acts.

  Have students use temperature probes during their scenario tests. They must record a rise in surface temperature and explicitly link it to the mechanical energy lost, reinforcing that total energy is conserved in the universe.

---

Methods used in this brief

• Inquiry Circle
• Think-Pair-Share
• Jigsaw