Sliding and Stuttering
Students use a spring scale to drag an object such as a ceramic coffee cup along a table top or the floor. The spring scale allows them to measure the frictional force that exists between the moving cup and the surface it slides on. By modifying the bottom surface of the cup, students find out what kinds of surfaces generate more or less friction.
Most coffee mugs (like the ones used in this activity) are made of glazed stoneware, which may look and feel smooth. This scanning electron micrograph of a piece of glazed stoneware, however, shows that at a magnification of ~7000X this material is not as smooth as we think.
Engineers must understand how friction affects all sorts of situations, from the bottom of skis in which friction is a disadvantage to hiking boots where friction provides helpful traction.
After this activity, students should be able to:
- Describe friction as a force that impedes motion.
- Distinguish between static friction and kinetic friction.
- Explain why friction occurs.