Science · Grade 5 · Forces and Simple Machines · Term 1

Measuring Force and Motion

Students will use tools to measure force and observe how forces cause changes in motion.

• Ontario Curriculum Expectations
• 3-PS2-1

About This Topic

Friction is the invisible force that opposes motion, and in this topic, Grade 5 students investigate how it affects everything from walking to the efficiency of machines. They learn that friction occurs whenever two surfaces rub together, converting kinetic energy into heat. The Ontario curriculum encourages students to explore how different materials and surface textures change the amount of friction produced. They also examine how we can increase friction for safety (like winter tires) or decrease it for efficiency (like using lubricants or ball bearings).

This topic is deeply connected to daily life in Canada, particularly in understanding how we adapt to icy winters. Students analyze the design of footwear, transportation systems, and sports equipment. By understanding friction, they gain insight into why machines wear out and how energy is 'lost' in mechanical systems. This knowledge is crucial for the subsequent study of energy conservation and sustainable design.

Students grasp this concept faster through structured investigation where they test various surfaces and measure the force needed to overcome friction.

Key Questions

1. Analyze how the magnitude of a force affects the acceleration of an object.
2. Differentiate between speed and velocity in describing an object's motion.
3. Construct a graph to represent the motion of an object over time.

Learning Objectives

• Calculate the net force acting on an object using Newton's second law of motion.
• Compare the velocity of an object under different applied forces.
• Construct a distance-time graph to represent an object's motion and interpret its slope.
• Explain how friction affects the motion of an object on different surfaces.
• Design an experiment to measure the force of friction between two surfaces.

Before You Start

Introduction to Forces

Why: Students need a basic understanding of what a force is before they can measure and analyze different types of forces like friction.

Describing Motion

Why: Prior knowledge of describing motion using terms like speed and direction is necessary to differentiate speed from velocity.

Key Vocabulary

Force	A push or a pull that can cause an object to change its motion, speed, or direction.
Friction	A force that opposes motion when two surfaces rub against each other, converting kinetic energy into heat.
Acceleration	The rate at which an object's velocity changes over time; it can be an increase, decrease, or change in direction.
Velocity	The speed of an object in a particular direction.
Net Force	The overall force acting on an object when all individual forces are combined. It determines the object's acceleration.

Watch Out for These Misconceptions

Common Misconception

Friction only happens between two solid objects.

What to Teach Instead

Students often forget about air resistance (drag) and water resistance. Teachers can use a simple experiment dropping a flat sheet of paper versus a crumpled ball to show that air also creates friction. Peer discussion about why swimmers wear caps can also surface this understanding.

Common Misconception

Friction is always a 'bad' force that we want to get rid of.

What to Teach Instead

Many students focus on friction slowing things down. Teachers should highlight that without friction, we couldn't walk, hold a pencil, or stop a bike. A 'friction hunt' around the school to find where friction is intentionally increased (like stair treads) helps correct this bias.

Active Learning Ideas

Inquiry Circle: The Friction Ramp

Groups test how far a toy car travels after rolling down a ramp onto different surfaces (carpet, sandpaper, wax paper, tile). They measure the distances, graph the results, and rank the surfaces from highest to lowest friction. They must explain their findings using the concept of surface texture.

50 min·Small Groups

Think-Pair-Share: The No-Friction World

Ask students to imagine a world where friction suddenly disappeared. In pairs, they list three things that would become impossible (like stopping a car) and three things that would become easier (like moving a heavy box). They share their 'chaos scenarios' with the class to highlight friction's dual nature.

20 min·Pairs

Station Rotations: Friction Fighters

Set up stations where students try to move a heavy block using different 'friction reducers': soap, oil, round pencils (rollers), and marbles (ball bearings). They use spring scales to quantify the reduction in force and discuss which method is most effective for different tasks.

45 min·Small Groups

Real-World Connections

• Engineers designing car brakes must understand friction to ensure vehicles can stop safely. They test brake pad materials and rotor designs to optimize the frictional force needed for deceleration.
• Athletes in sports like curling use knowledge of friction to control the motion of stones on ice. They adjust the surface of the ice and the technique used to apply spin, influencing how far the stone travels.
• Manufacturers of skis and snowboards adjust the base materials and wax to control friction. This allows for faster gliding on snow while maintaining control during turns and jumps.

Assessment Ideas

Quick Check

Present students with a scenario: 'A box is pushed across a floor with a force of 10 N, and friction opposes the motion with a force of 3 N.' Ask students to calculate the net force and state the direction of motion. Review answers as a class.

Exit Ticket

Provide students with a simple distance-time graph showing an object moving at a constant speed, then stopping. Ask them to write two sentences describing the object's motion during the first part of the graph and two sentences describing its motion when it stopped.

Discussion Prompt

Pose the question: 'How could you design an experiment to compare the friction between a wooden block and a carpet versus the same block on a tile floor?' Guide students to identify variables to control (e.g., mass of the block) and how to measure the force of friction (e.g., using a spring scale).

Frequently Asked Questions

What factors affect the amount of friction between two surfaces?

The two main factors are the types of surfaces in contact (rough vs. smooth) and how hard the surfaces are pressed together (weight). Rougher surfaces have more 'peaks and valleys' that catch on each other, creating more resistance, while heavier objects press those surfaces together more firmly.

How does friction relate to heat energy?

When two surfaces rub together, the energy of motion is converted into thermal energy. This is why rubbing your hands together makes them warm. In machines, this heat is often considered 'wasted' energy because it doesn't help the machine do its job and can cause parts to wear out.

How can active learning help students understand friction?

Active learning allows students to feel the force of friction. Using spring scales to pull objects across different textures provides immediate, quantifiable data. When students physically struggle to pull a block over sandpaper compared to ice, the concept of 'opposing force' moves from a textbook definition to a lived experience.

How do we use friction to stay safe during Canadian winters?

We use friction in many ways, such as putting winter tires with deep treads on cars, spreading sand or salt on icy sidewalks to increase grip, and wearing boots with rubber soles. Understanding friction helps students make safe choices and understand the technology behind winter safety.