Physics · 9th Grade

Active learning ideas

Friction and Air Resistance

Active learning lets students directly measure friction forces and observe air resistance effects, turning abstract concepts into tangible experiences. These hands-on activities expose the invisible forces that shape motion, helping students connect theory with real-world behavior.

• Common Core State Standards
• HS-PS2-1
• HS-ETS1-3

• 15–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Inquiry Circle
• 45 min · Small Groups

Inquiry Circle: Coefficient of Friction Lab

Groups use spring scales to measure the force needed to start a block sliding (static friction) and the force needed to keep it moving (kinetic friction) on wood, sandpaper, and a rubber mat. They calculate both coefficients for each surface and compare results across groups to discuss variability.

What is the molecular cause of friction between two seemingly smooth surfaces?

Facilitation Tip

In the Aerodynamic Drag simulation, have students run trials with the same object at 5 m/s, 10 m/s, and 15 m/s to connect speed directly to drag force.

What to look for

Provide students with a scenario: 'A 10 kg box rests on a horizontal surface. The coefficient of static friction is 0.5 and kinetic friction is 0.3.' Ask them to calculate the maximum static friction force and the kinetic friction force. Then, ask them to explain which force is larger and why.

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

Activity 02

• Gallery Walk
• 30 min · Small Groups

Gallery Walk: Friction in Engineering

Stations feature images of tire tread patterns, brake pad materials, ski wax selection, and engine lubricants. Groups identify whether each design aims to increase or decrease friction, explain the physics behind the design choice, and connect the goal to the coefficient of friction concept.

Why is static friction generally greater than kinetic friction?

What to look for

Display images of different objects falling (e.g., a feather, a bowling ball, a skydiver). Ask students to write down for each object whether air resistance plays a significant role in its fall and why. Discuss their answers as a class.

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Activity 03

• Think-Pair-Share
• 15 min · Pairs

Think-Pair-Share: Static vs. Kinetic Transition

Pairs discuss a scenario: you push a heavy couch that will not budge, then it suddenly starts sliding and feels easier to push. They must explain the transition from maximum static friction to kinetic friction and why the required force decreases the instant motion begins.

How do automotive engineers minimize drag to improve fuel efficiency?

What to look for

Pose the question: 'Imagine you are designing a new type of shoe sole. What factors related to friction would you consider to ensure good grip on wet pavement?' Facilitate a discussion where students identify the need for a high coefficient of kinetic friction and potentially different surface textures.

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

Activity 04

• Simulation Game
• 35 min · Pairs

Simulation Game: Aerodynamic Drag and Terminal Velocity

Using a digital simulation, students drop objects of different shapes and densities, observing when each reaches terminal velocity. They compare time-to-terminal across objects and connect the drag force to cross-sectional area, speed, and fluid density.

What is the molecular cause of friction between two seemingly smooth surfaces?

What to look for

Provide students with a scenario: 'A 10 kg box rests on a horizontal surface. The coefficient of static friction is 0.5 and kinetic friction is 0.3.' Ask them to calculate the maximum static friction force and the kinetic friction force. Then, ask them to explain which force is larger and why.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

A few notes on teaching this unit

Teach friction by starting with simple blocks on flat surfaces, then move to variable inclines to visualize normal force changes. For air resistance, use simulations to isolate variables like cross-sectional area and speed before discussing real engineering contexts. Avoid overemphasizing surface area for friction; instead, focus on the normal force and material pairs.

Students will accurately calculate friction forces, explain how surface properties affect grip, and predict how shape influences air resistance. They will also justify design choices using evidence from investigations and simulations.

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Watch Out for These Misconceptions

• During Collaborative Investigation: Coefficient of Friction Lab, watch for students who assume a larger block face will produce more friction because it has more surface area in contact.

  Have students measure friction using the spring scale for both the large and small faces of the same block, then compare readings. Ask them to explain why the forces are nearly identical, referencing the equation F = μN and how pressure changes with area.

• During Think-Pair-Share: Static vs. Kinetic Transition, watch for students who think static friction always equals its maximum value μN whenever an object is at rest.

  Ask pairs to slowly increase the force applied via the spring scale until the block just begins to move. Have them record the force at the moment before motion and the force at the moment motion starts, then compare the two values to see that static friction adjusts to match the applied force up to the maximum.

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Methods used in this brief

• Inquiry Circle
• Gallery Walk
• Think-Pair-Share
• Simulation Game