2.2 Forces and Free-Body Diagrams

Describe a force as an interaction between two objects or systems.

• Forces are vector quantities that describe the interactions between objects or systems.
  • i. A force exerted on an object or system is always due to the interaction of that object with another object or system.
  • ii. An object or system cannot exert a net force on itself.
• Contact forces describe the interaction of an object or system touching another object or system and are macroscopic effects of interatomic electric forces. TOPIC 2.2 Forces and Free-Body Diagrams

Describe the forces exerted on an object or system using a free-body diagram.

• Free-body diagrams are useful tools for visualizing forces being exerted on a single object or system and for determining the equations that represent a physical situation.
• The free-body diagram of an object or system shows each of the forces exerted on the object by the environment.
• Forces exerted on an object or system are represented as vectors originating from the representation of the center of mass, such as a dot. A system is treated as though all of its mass is located at the center of mass. AP Physics 1: Algebra-Based Course and Exam Description Force and Translational Dynamics UNIT 2
• A coordinate system with one axis parallel to the direction of acceleration of the object or system simplifies the translation from freebody diagram to algebraic representation. For example, in a free-body diagram of an object on an inclined plane, it is useful to set one axis parallel to the surface of the incline. BOUNDARY STATEMENT AP Physics 1 only expects students to depict the forces exerted on objects, not the force components on free-body diagrams. On the AP Physics exams, individual forces represented on a free-body diagram must be drawn as individual straight arrows, originating on the dot and pointing in the direction of the force. Individual forces that are in the same direction must be drawn side by side, not overlapping. AP Physics 1: Algebra-Based Course and Exam Description Force and Translational Dynamics UNIT 2 TOPIC 2.3 Newton’s Third Law