Science · Grade 2 · Movement and Simple Machines · Term 4

Friction: The Stopping Force

Students will investigate friction as a force that slows down or stops moving objects.

• Ontario Curriculum Expectations
• 2-PS1-1

About This Topic

The Design Challenge is the culminating topic where students apply their knowledge of forces and simple machines to solve a real-world problem. In the Ontario Grade 2 curriculum, this aligns with the STEM Skills and Connections expectations, encouraging students to use a design process: planning, building, testing, and improving. Students are challenged to create a device that can move an object a certain distance or perform a specific task using the principles they have learned.

This topic fosters creativity, resilience, and collaborative problem-solving. It is the ultimate active learning experience, as students move from theory to practice. By working in teams to build and refine their designs, they learn that 'failure' is just a step in the engineering process. This hands-on challenge reinforces their understanding of physical science while building the 'soft skills' of teamwork and critical thinking that are essential for future success.

Key Questions

1. Explain how friction helps a car stop.
2. Compare the amount of friction on smooth and rough surfaces.
3. Predict how friction will affect a toy car rolling down a ramp.

Learning Objectives

• Compare the effect of different surfaces on the distance a toy car travels.
• Explain how friction acts as a force to slow down or stop moving objects.
• Predict how changing the surface of a ramp will affect the speed of a rolling object.
• Demonstrate how friction is used to stop a bicycle.

Before You Start

Push and Pull Forces

Why: Students need to understand that forces are pushes or pulls before they can investigate how friction opposes motion.

Objects in Motion

Why: Understanding that objects move is fundamental to exploring forces that can start, stop, or change their motion.

Key Vocabulary

friction	A force that opposes motion when two surfaces rub against each other. It slows things down.
surface	The outside part or layer of an object. Different surfaces can feel smooth or rough.
force	A push or a pull that can make an object move, stop moving, or change direction.
motion	The act or process of moving or being moved. When something is moving, it is in motion.

Watch Out for These Misconceptions

Common Misconception

The first design should work perfectly.

What to Teach Instead

Students can get frustrated when their machine fails. Use the 'Redesign Phase' to teach that engineers expect things to break or not work at first, and that 'testing and improving' is the most important part of science.

Common Misconception

More materials make a better machine.

What to Teach Instead

Children often try to use every craft supply available. Encourage 'minimalist engineering' by challenging them to solve the problem with the fewest pieces possible, focusing on the function of the simple machines rather than decoration.

Active Learning Ideas

Inquiry Circle: The Great Cargo Move

Groups must design a way to move a 'heavy load' (a bag of marbles) across a 2-meter gap without touching the load directly. they must use at least two different simple machines in their design.

60 min·Small Groups

Think-Pair-Share: The Redesign Phase

After a first round of testing their machines, students think about one thing that didn't work. They pair up with a member of another group to get a 'fresh pair of eyes' on their problem before going back to improve their design.

20 min·Pairs

Gallery Walk: Engineering Expo

Once designs are complete, the class holds an 'expo.' Half the groups stay to demonstrate their machines while the other half rotates to ask questions and provide positive feedback on the designs.

40 min·Whole Class

Real-World Connections

• Bicycle brakes use friction to stop the wheels. When you squeeze the brake levers, pads press against the wheel rim, creating friction that slows the bike down. This is essential for safe riding in busy streets or on downhill paths.
• Tire manufacturers design treads to create friction between the tires and the road. This grip is crucial for accelerating, steering, and stopping safely in various weather conditions, from dry highways to wet or icy roads.

Assessment Ideas

Exit Ticket

Give students a toy car and two different surfaces (e.g., a smooth tile and a carpet square). Ask them to roll the car down a small ramp onto each surface and record how far it travels. On the ticket, they should write: 'Which surface made the car stop faster? Why?'

Quick Check

Ask students to stand up and pretend to ride a bicycle. Prompt them: 'Show me how you would use friction to stop your bike.' Observe if they demonstrate a pulling or squeezing motion, mimicking brake use.

Discussion Prompt

Pose the question: 'Imagine you are designing a slide at a playground. Would you want a high friction surface or a low friction surface for the slide? Explain your choice using the word 'friction'.'

Frequently Asked Questions

What is the 'Design Process' for Grade 2?

At this level, it's a simple four-step loop: 1. Think (What is the problem?), 2. Plan (Draw a picture), 3. Do (Build and test it), and 4. Fix (How can we make it better?).

How do I assess a design challenge fairly?

Focus on the process rather than just the final product. Look for how well students collaborated, how they handled setbacks, and whether they can explain which scientific principles (like a ramp or a push) they used in their design.

How can active learning help students with the design challenge?

The design challenge *is* active learning in its purest form. It requires students to take ownership of their learning, apply abstract concepts to physical materials, and engage in constant peer-to-peer feedback. This active engagement ensures the science 'sticks' because they've used it to achieve a goal.

What materials are best for a Grade 2 design challenge?

Recycled materials are perfect: cardboard tubes, plastic bottles, string, rubber bands, masking tape, and wooden skewers. These are safe, easy to manipulate, and encourage students to see the potential in everyday objects.