Discovering Friction
Graphite crystals consist of hexagonal arrays of carbon molecules that form two-dimensional, crystalline plates. This structure allows the plates to slide freely over one another, making graphite a very useful lubricating material.
With a simple demonstration activity, students are introduced to the concept of friction as a force that impedes motion when two surfaces are in contact. Then, in the associated activity, Sliding and Stuttering, they work in teams to use a spring scale to drag an object such as a ceramic coffee cup along a table top or the floor. They use the spring scale to measure the frictional force that exists between the moving cup and the surface on which it slides. By modifying the bottom surface of the cup, students experiment to find out what kinds of surfaces generate more or less friction. They also discover that both static and kinetic friction are involved when an object initially at rest is caused to slide across a surface.
Whether engineers are trying to design a better set of automobile brakes or a more efficient wind turbine, a thorough understanding of friction is a vital prerequisite. Engineers must understand how friction affects all sorts of everyday situations, from the bottom of skis in which friction is a disadvantage to hiking boots where friction provides important traction.
After this lesson, students should be able to:
- Describe friction as a force that impedes motion and generates heat.
- Distinguish between static friction and kinetic friction.
- Explain why friction occurs.
- Describe common occurrences of friction, including those in which friction can be used to advantage in everyday life.
- Describe ways in which friction can be reduced.