Science · Grade 8

Active learning ideas

Efficiency and Friction

Active learning builds deep understanding of efficiency and friction by letting students feel the difference between idealized calculations and real-world results. When students measure forces in simple machines, they see firsthand why no system reaches perfect efficiency and how friction shapes their designs.

• Ontario Curriculum Expectations
• NGSS.MS-PS3-3

• 30–50 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Stations Rotation
• 45 min · Small Groups

Stations Rotation: Friction Surfaces

Prepare three stations with ramps covered in smooth tape, sandpaper, and wax. Students release identical toy cars from the top, measure travel distances and times with rulers and stopwatches, then graph results to compare friction effects. Conclude with class discussion on patterns.

Explain why no machine can be 100% efficient.

Facilitation Tip

During Station Rotation: Friction Surfaces, assign each group a specific surface type and provide identical weights so students focus only on friction’s role.

What to look for

Provide students with data from a simple machine experiment (e.g., a pulley system). Ask them to calculate the efficiency using the formula: (Output Work / Input Work) x 100%. Review calculations to identify common errors.

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

Activity 02

• Case Study Analysis
• 35 min · Pairs

Pairs Lab: Pulley Efficiency

Pairs construct a single and double pulley system using string, weights, and a meter stick. They lift a load while measuring input force and distance, calculate output work and efficiency, then modify with lubricants and retest. Record data in tables for analysis.

Analyze the impact of friction on the efficiency of mechanical systems.

Facilitation Tip

For Pairs Lab: Pulley Efficiency, pre-load the pulley system with known masses to ensure consistent starting conditions for all pairs.

What to look for

Pose the question: 'Imagine a perfectly frictionless world. What would be the benefits and drawbacks for everyday machines like cars or bicycles?' Facilitate a class discussion on the necessity and impact of friction.

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

Activity 03

• Case Study Analysis
• 50 min · Small Groups

Design Challenge: Low-Friction Vehicle

Teams build balloon-powered cars from recyclables, testing on various tracks. Measure push distance versus travel distance, compute efficiency, and redesign with smoother wheels or lubricants. Present best designs to class with efficiency data.

Design strategies to minimize energy loss due to friction.

Facilitation Tip

In Design Challenge: Low-Friction Vehicle, require students to document at least three design changes and explain how each reduces friction.

What to look for

Ask students to write down two ways friction affects mechanical systems and one strategy they could use to reduce friction in a specific device, such as a skateboard.

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

Activity 04

• Case Study Analysis
• 30 min · Whole Class

Whole Class Demo: Ramp Work

Demonstrate pushing a block up ramps of varying angles, using spring scales for force and measuring heights. Class calculates input/output work together on shared whiteboard, then predicts efficiency trends for steeper ramps.

Explain why no machine can be 100% efficient.

Facilitation Tip

During Whole Class Demo: Ramp Work, use a spring scale with clear markings so students can read input force accurately without confusion.

What to look for

Provide students with data from a simple machine experiment (e.g., a pulley system). Ask them to calculate the efficiency using the formula: (Output Work / Input Work) x 100%. Review calculations to identify common errors.

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

A few notes on teaching this unit

Teach this topic by starting with hands-on measurements before introducing formulas, as students need concrete evidence before believing efficiency is always less than 100 percent. Avoid rushing to the efficiency formula—let students grapple with the concept through repeated trials and data collection. Research shows that students retain concepts better when they discover the relationship between work input and output through their own experiments rather than a lecture.

Successful learning looks like students accurately calculating efficiency using real data, identifying friction as a major energy converter, and redesigning systems to minimize losses. They should connect their findings to broader contexts, such as why bike chains need oil or why car engines overheat without coolant.

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Watch Out for These Misconceptions

• During Station Rotation: Friction Surfaces, watch for...

  Students may assume that smoother surfaces always produce higher efficiency. Redirect them by having groups compare their surface data with their calculated efficiency to show that surface roughness isn’t the only factor—load weight and contact area also matter.

• During Design Challenge: Low-Friction Vehicle, watch for...

  Students might believe any reduction in friction improves efficiency. Use the challenge’s requirement to document design changes to guide them toward testing one variable at a time, such as axle materials or wheel size.

• During Pairs Lab: Pulley Efficiency, watch for...

  Students may focus only on speed when comparing trials. Have them complete the lab’s data table side by side with input work and output work columns, then ask them to explain why efficiency doesn’t depend on how fast the load is lifted.

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Methods used in this brief

• Stations Rotation
• Case Study Analysis