Today we learned about the force that works against motion: friction. Our students explored the force of friction by experimenting with a coffee mug sliding down an inclined plane. First, students tested the mug sliding by itself. They then tested the effect of adding different surfaces to the bottom of the mug. Some surfaces decreased the friction (made the mug more slippery!) and some increased the friction. Some students may also have discovered that adding mass to the mug and making it heavier increased the friction between the mug and the inclined plane. They 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. Challenge your student to spend an hour paying attention to where they experience friction, either as a “good” thing or a “bad” thing.