← Unit 2: Dynamics
Newton's Laws & Free-Body Diagrams
Newton's second law, ΣF = ma, is applied by drawing a free-body diagram showing every force acting on an object, then summing forces along each axis.
Overview
Newton's First Law: an object at rest/constant velocity stays that way unless a net force acts. Second Law: ΣF = ma. Third Law: forces come in equal-and-opposite action-reaction pairs acting on DIFFERENT objects. A free-body diagram isolates one object and draws only the forces acting ON it.
Practice Quiz
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A book rests on a table. By Newton's Third Law, the reaction force to 'the table pushes up on the book' is: