Grade 8 Science Lesson: Friction
Objective:
By the end of this lesson, students will be able to:
1. Define friction and explain how it works.
2. Identify the types of friction.
3. Understand the factors that affect the amount of friction between two surfaces.
4. Explain real-life examples where friction is both useful and problematic.
Materials Needed:
● Whiteboard and markers
● Various materials to demonstrate friction (e.g., different types of surfaces such as
rubber, cloth, wood, metal)
● Objects to slide on those surfaces (e.g., books, blocks, toy cars)
● Friction worksheet (optional)
● Access to video or animation about friction (optional)
Introduction (10 minutes):
1. Hook: Ask students:
○ "Have you ever tried to slide a heavy book across a table? What happens? Why
do you think the book doesn’t just keep sliding forever?"
○ Let the students share their experiences. They will likely talk about how the book
slows down and stops due to the force acting against it.
2. Key Concept: Introduce friction as a force that resists the motion of two objects sliding
past each other. Explain that friction is why things don’t keep moving forever and why we
need force to overcome it.
Main Lesson (25 minutes):
1. What is Friction? (10 minutes):
● Definition: Friction is a force that opposes the relative motion or tendency of such
motion of two surfaces in contact. It acts in the opposite direction to the movement of an
object.
● Key Fact: Friction is caused by the microscopic roughness of surfaces. Even smooth
surfaces have tiny bumps that create resistance when they slide against each other.
2. Types of Friction (10 minutes):
There are several types of friction that act in different situations:
1. Static Friction:
○ What it is: This is the friction that keeps an object at rest and prevents it from
starting to move. It must be overcome to get an object moving.
○ Example: A book on a table does not move until you push it with enough force to
overcome the static friction.
2. Kinetic Friction:
○ What it is: This is the friction that acts when an object is already in motion.
○ Example: Once the book starts sliding, the friction between the book and the
table is kinetic friction.
3. Rolling Friction:
○ What it is: This friction occurs when an object rolls over a surface. It is generally
much smaller than static or kinetic friction.
○ Example: A ball rolling across the floor experiences rolling friction, which is why
it eventually slows down and stops.
4. Fluid Friction:
○ What it is: This friction occurs when an object moves through a fluid, such as air
or water.
○ Example: The friction between a moving car and the air (air resistance) or the
friction between a fish and water.
3. Factors Affecting Friction (5 minutes):
Several factors affect the amount of friction between two surfaces:
1. Roughness of the surfaces:
○ The rougher the surfaces in contact, the greater the friction.
○ Example: Sandpaper on wood produces more friction than a smooth piece of
paper.
2. Normal force (the force pressing the surfaces together):
○ The greater the force pressing the surfaces together, the greater the friction.
○ Example: If you push harder on an object, it will create more friction.
3. Type of materials:
○ Different materials produce different amounts of friction. Rubber on concrete
creates more friction than steel on ice.
○ Example: Tires on a road create more friction than metal skates on ice.
Demonstration (Optional – 5 minutes):
To visually demonstrate friction, conduct a simple experiment using a block and different
surfaces:
1. Place a block of wood (or any object) on different surfaces (smooth, rough, carpeted,
etc.).
2. Gently push the block and observe how much force it takes to get it moving and keep it
moving.
3. Discuss how the rougher surfaces create more friction, and smoother surfaces create
less.
Closing (5 minutes):
● Review: Ask students to define friction and explain the types of friction they learned
about.
● Quick Question: "Can you think of a situation where friction is helpful and one where it’s
not so helpful?"
○ Helpful: Friction between shoes and the ground helps us walk without slipping.
○ Not Helpful: Friction between the brakes and the wheels of a car can slow it
down too much if not managed properly.
Homework Assignment:
● Reflection: Write a short paragraph explaining how friction affects daily life. How does
friction help or hinder certain tasks (e.g., walking, driving, or playing sports)?
● Extra Challenge: Research how engineers reduce friction in certain machines (like car
engines) and explain how they do it.
Assessment:
● Informal assessment through participation in class discussions and the hands-on
experiment.
● Review homework for understanding of friction and its types.
