Science · Year 7 · Forces in Motion · Term 2

Friction and Air Resistance

Students will explore friction and air resistance as forces that oppose motion, and investigate factors that affect their magnitude.

• ACARA Content Descriptions
• AC9S7U04

About This Topic

Friction and air resistance act as forces that oppose the motion of objects. Friction occurs between surfaces in contact, such as a shoe on a footpath, and depends on surface roughness, weight, and speed. Air resistance pushes against objects moving through air, increasing with speed, surface area, and shape. Year 7 students test these factors through experiments, like sliding blocks on sandpaper versus glass, or dropping parachutes of different sizes. These investigations directly address AC9S7U04 by developing skills in fair testing and data analysis.

In the forces and motion unit, this topic connects friction to everyday actions like braking bicycles or gripping cricket bats, while air resistance explains streamlining in cars or cycling helmets. Students learn to identify variables, control conditions, and draw conclusions from patterns in results. This builds a foundation for understanding balanced and unbalanced forces.

Active learning suits this topic perfectly. Students gain clear insights by measuring distances on ramps or timing falls from heights. Group experiments encourage prediction, observation, and discussion, turning abstract forces into measurable realities that stick with students.

Key Questions

1. Analyze how different surfaces affect the amount of friction generated.
2. Explain the importance of friction in everyday activities.
3. Design an experiment to investigate the effect of surface area on air resistance.

Learning Objectives

• Compare the frictional force generated between different pairs of surfaces.
• Analyze how surface area and shape influence air resistance.
• Explain the role of friction in everyday activities, such as walking or braking.
• Design an experiment to test the effect of one variable (e.g., speed, surface) on air resistance.

Before You Start

Introduction to Forces

Why: Students need a basic understanding of what a force is and that forces can cause motion or changes in motion.

Measurement and Units

Why: Students will need to measure distances, times, and potentially masses to compare the effects of friction and air resistance.

Key Vocabulary

Friction	A force that opposes motion when two surfaces rub against each other. It can make it harder for objects to move or stop them from moving.
Air Resistance	A type of friction that opposes the motion of an object moving through the air. It is also known as drag.
Surface Area	The total area of the outside surfaces of an object. A larger surface area can increase air resistance.
Roughness	The degree to which a surface is uneven or not smooth. Rougher surfaces generally create more friction.
Force	A push or pull that can cause an object to change its motion, speed, or direction.

Watch Out for These Misconceptions

Common Misconception

Air resistance only affects fast-moving objects like planes.

What to Teach Instead

All moving objects face air resistance, even slow ones like falling leaves. Drop tests with feathers and coins reveal this clearly. Peer observation and timing activities correct the idea, showing proportional effects.

Common Misconception

Larger surface area always increases friction the same way.

What to Teach Instead

Surface area affects air resistance more than contact friction. Parachute experiments demonstrate this distinction. Students refine ideas through redesign trials and data sharing.

Active Learning Ideas

Ramp Testing: Surface Friction

Provide ramps and toy cars or blocks. Students test smooth wood, carpet, and sandpaper surfaces, measuring distance traveled after release from a fixed height. They record times and distances in tables, then graph results to compare friction effects.

45 min·Small Groups

Parachute Drop: Air Resistance

Cut plastic bags into squares of varying sizes, attach strings and weights. Students drop parachutes from a balcony or stairs, timing descent with stopwatches. They discuss how surface area changes fall speed and redesign for slowest drop.

35 min·Pairs

Streamlining Challenge: Shape Effects

Students shape paper into balls, cones, and flat sheets, dropping them together from height. Use phones to video slow-motion falls, measure times, and note drag differences. Groups present findings on best shapes for minimal resistance.

40 min·Small Groups

Whole Class Demo: Friction Factors

Demonstrate a weighted block sliding on a tilted board, adding weights or changing tilt. Class predicts and times slides, votes on key factors, then breaks into pairs to replicate with own materials.

30 min·Whole Class

Real-World Connections

• Automotive engineers design car bodies with smooth, aerodynamic shapes to reduce air resistance, improving fuel efficiency and allowing for higher speeds on highways.
• Professional cyclists wear tight-fitting suits and helmets to minimize air resistance, helping them achieve faster race times in events like the Tour de France.
• Ski resorts use grooming machines to create smooth ski runs, reducing friction between skis and snow to allow for faster downhill skiing.

Assessment Ideas

Exit Ticket

Provide students with a scenario: 'A car is driving down a road.' Ask them to write down two forces acting on the car that oppose its motion and explain how changing the car's shape might affect one of these forces.

Quick Check

Show students images of different objects (e.g., a flat sheet of paper, a crumpled ball of paper, a feather, a brick). Ask them to predict which object will fall fastest through the air and explain their reasoning based on air resistance.

Discussion Prompt

Pose the question: 'Imagine you are designing a new type of shoe sole. What features would you include to increase friction for walking on wet surfaces, and why?' Facilitate a class discussion where students share their ideas and justify their design choices.

Frequently Asked Questions

How do you design experiments to test friction factors?

Start with a clear question, like how surface type affects sliding distance. Use identical ramps, release heights, and objects as controls. Students measure and repeat trials three times for reliability, then average data. This structure teaches fair testing while linking to real scenarios like playground slides.

What everyday examples illustrate air resistance?

Parachutes slow skydivers, helmets reduce drag for cyclists, and dimples on golf balls minimize resistance. Students connect these by testing paper shapes. Discussing applications reinforces why streamlining matters in design, from Formula 1 cars to running shoes.

How can active learning help students grasp friction and air resistance?

Active approaches make forces tangible: students push carts on varied surfaces or drop objects to see opposition firsthand. Collaborative timing and graphing reveal patterns lectures miss. Prediction sheets before tests build engagement, while redesigns teach iteration, boosting retention and inquiry confidence.

How does this topic align with Australian Curriculum standards?

AC9S7U04 requires investigating forces like friction and air resistance through experiments. Activities develop skills in planning, variables, and evidence analysis. Connect to unit questions on surfaces, everyday importance, and surface area effects, preparing students for motion assessments.