Friction on different surfaces
Pull a wooden block across glass, wood, sandpaper and oiled wood with a spring balance, and find the force that just starts it moving.
Core concept
Rougher surfaces and heavier objects give more friction
Topic: Force and motion
friction: A force that slows things down when two surfaces rub together. All key words is a force: A push or a pull. Forces can start, stop or turn things. All key words that acts between two surfaces and opposes motion. When you pull gently on a block, friction pulls back just as hard, so the block stays still. As you pull harder, friction grows too, but only up to a limit. When your pull beats that limit, the block starts to slide. Rough surfaces have more friction than smooth ones, and pressing the surfaces together harder (a heavier block) increases friction. Oil or grease reduces friction.
What you will learn
- Measure the force needed to start a block moving on different surfaces.
- Explain how the roughness of a surface and the weight of an object affect friction.
- Give examples of useful friction and ways to reduce friction.
Before you start
- Know that a force is a push or a pull measured in newtons (N).
Materials
- Wooden blocks of 0.5 kg, 1 kg and 2 kg
- Sandpaper and a few drops of oil
Equipment
- Spring balance (0 to 20 N)
- Glass sheet and wooden board
Procedure
- Choose a surface. Increase the pull on the spring balance step by step until the block just starts to slide.
- Record the smallest pull that starts the block moving.
- Repeat on the other surfaces.
- Use the heavier block on wood and find the pull that starts it moving.
How this simulation is simplified
- g is taken as 10 N/kg.
- Each surface has fixed coefficients of friction for wood sliding on it.