A set-up comprising a magnetic disc, a solenoid and a mechanical balance was used to teach first-year physics students Newton's third law with the help of a free body diagram. The image of a floating magnet immobilized by the solenoid's repulsive force should help dispel a common misconception of students as regards the first law: that stationary objects are not being acted on by any force at all. Dropping the magnet onto the electrified solenoid, which can change polarity, can lead to more sophisticated elaboration of the second law. (Contains 5 figures.)