Free Body Diagrams
Free body diagrams help you visualize all forces acting on an object. Each scenario shows different force combinations that determine an object's motion.
For a brick resting on a table, you'd draw two forces: the weight pointing downward and the normal force pointing upward. These forces balance each other perfectly.
When a brick slides at constant speed, the diagram includes four forces: weight downward, normal force upward, applied force in the direction of motion, and friction opposing motion. Since speed is constant, these forces must balance completely.
Think about it: A skydiver reaching terminal velocity experiences balanced forces - gravity pulling down equals air resistance pushing up. That's why they stop accelerating!
For a brick slowing down, the frictional force exceeds the applied force, creating net force opposite to motion. This causes negative acceleration (deceleration).
