Physics · Grade 11

Active learning ideas

Non-Conservative Forces and Energy Loss

This topic often feels abstract to students because energy ‘loss’ implies disappearance rather than transformation. Active, hands-on stations and simulations let students directly observe friction’s effects, making the invisible work of non-conservative forces visible and measurable. The physical sensations of rubbing hands or watching a pendulum slow down anchor the concept in lived experience, reducing reliance on abstract equations alone.

• Ontario Curriculum Expectations
• HS-PS3-3

• 20–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Stations Rotation
• 45 min · Small Groups

Stations Rotation: Friction Surfaces

Prepare stations with ramps covered in sandpaper, cloth, ice, and smooth wood. Students release identical balls from the same height, measure distances traveled, and calculate speeds using timers. Groups record data in tables and graph friction force versus surface type.

Differentiate between conservative and non-conservative forces, providing examples of each.

Facilitation Tip

During Station Rotation: Friction Surfaces, place identical blocks on different surfaces and ask students to predict which will stop first based on texture; this primes discussion about energy conversion before data collection.

What to look for

Present students with scenarios: a ball dropped from a height, a block sliding down a rough incline, a pendulum swinging. Ask them to identify the forces acting in each scenario and classify them as conservative or non-conservative. Then, have them predict whether mechanical energy is conserved.

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Activity 02

• Case Study Analysis
• 35 min · Pairs

Pendulum Comparison Lab

Set up two pendulums: one in air, one submerged in viscous fluid. Students measure swing amplitudes over 20 cycles, plot decay curves, and compute fractional energy loss per swing. Discuss system boundaries and energy transfers in pairs.

Analyze how friction affects the total mechanical energy of a system.

Facilitation Tip

In the Pendulum Comparison Lab, use two pendulums with different string materials to isolate the role of air resistance versus friction at the pivot; this helps students disentangle overlapping non-conservative effects.

What to look for

Provide students with a diagram of a block sliding down a ramp with friction. Ask them to write two equations: one representing the change in mechanical energy and one representing the total energy conservation, clearly identifying the work done by friction.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

Activity 03

• Case Study Analysis
• 30 min · Pairs

Energy Skate Park Simulation

Use PhET simulation for virtual skate park. Students design tracks with/without friction, adjust mass and height, and track kinetic, potential, and thermal energy bars. Export graphs to analyze total energy conservation.

Explain how energy is conserved even when mechanical energy is 'lost' due to friction.

Facilitation Tip

In the Energy Skate Park Simulation, set the friction slider to zero first so students observe energy conservation before adding friction, making the loss more meaningful when it appears.

What to look for

Facilitate a class discussion using the prompt: 'Imagine a skateboarder rolling to a stop on a flat surface. Where does the skateboarder's initial kinetic energy go? Explain the role of friction and other non-conservative forces in this energy transformation.'

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

Activity 04

• Case Study Analysis
• 20 min · Whole Class

Whole Class Demo: Rubbing Hands

Lead a demo where students rub hands vigorously, then measure temperature rise with infrared thermometer. Extend to inclined plane with brake pad; calculate work done by friction from height loss. Class discusses conversions.

Differentiate between conservative and non-conservative forces, providing examples of each.

Facilitation Tip

During the Whole Class Demo: Rubbing Hands, have students press their palms together with increasing pressure and time the duration until they feel warmth; this turns qualitative sensation into a quantitative starting point for energy calculations.

What to look for

Present students with scenarios: a ball dropped from a height, a block sliding down a rough incline, a pendulum swinging. Ask them to identify the forces acting in each scenario and classify them as conservative or non-conservative. Then, have them predict whether mechanical energy is conserved.

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

A few notes on teaching this unit

Start with a concrete, relatable example like a skateboard slowing down to introduce non-conservative forces, then contrast it with a falling ball to highlight when mechanical energy is conserved. Avoid overwhelming students with too many force types at once; focus first on friction and air resistance as the primary non-conservative forces they will analyze. Research shows that students grasp energy transformations better when they connect equations to physical sensations, so pair calculations with tactile experiences like rubbing surfaces together.

Students will confidently classify forces as conservative or non-conservative, explain how energy transforms from mechanical to thermal, and calculate the energy lost due to friction in real-world scenarios. They will also articulate why mechanical energy is not always conserved and support their reasoning with data from their own experiments.

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Watch Out for These Misconceptions

• During Station Rotation: Friction Surfaces, watch for students stating that friction destroys energy. Redirect them by asking them to touch the block and surface after sliding, then connect the heat they feel to the mechanical energy converted into thermal energy.

  Have students measure the block’s temperature change before and after sliding to calculate the energy lost as heat, explicitly linking the thermal energy gained by the block to the mechanical energy lost by the system.

• During Pendulum Comparison Lab, listen for students claiming mechanical energy is always conserved. Redirect them by asking them to compare the starting and ending amplitudes of their pendulums over multiple swings.

  Ask students to graph the pendulum’s maximum height over time and use the graph to calculate the energy lost per swing, then connect this loss to the work done by air resistance and pivot friction.

• During Station Rotation: Friction Surfaces, note if students assume all forces are non-conservative. Redirect them by asking them to identify which forces depend on the path taken and which do not.

  Provide a scenario where students must calculate the work done by gravity versus friction on different paths between the same two points, emphasizing that gravity’s work is path-independent while friction’s is not.

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Methods used in this brief

• Stations Rotation
• Case Study Analysis