Friction – Slip Sliding Away, or Not?
Today our students were materials scientists! They explored the forces of friction using a spring scale, a coffee mug (empty!), and several different surfaces that they stuck to the bottom of the mugs. They needed a steady hand, good teamwork, and keen observational skills. Students measured two types of friction: static friction, which is the force that opposes setting an object in motion, and kinetic friction, which is the force that opposes keeping an object in motion. They found that although the size of the frictional force could be quite different, depending on the surfaces that were sliding, the static friction for any surface was always greater than the kinetic friction for that surface.
Frictional forces are important in engineering too! In our discussion, we also considered when friction was helpful (braking a car or bicycle, walking along without slipping, grabbing hold of an object), and when it was unhelpful (making machinery overheat!) and needed to be minimized. You can challenge your student to spend an hour paying attention to where she/he experiences friction, either as a “good” thing or a “bad” thing.