Or FORCE-BODY-DIAGRAMS FREE-BODY-DIAGRAMS Or FORCE-BODY-DIAGRAMS & NEWTON’S LAWS

The analysis of dynamics problems involves the selection and analysis of the relevant forces acting on the object under consideration. The object of interest is referred to as the system. The world around the object that exerts forces on it is called the environment. system

Each force has a specific identifiable, immediate cause called agent. The agent can be animate such as a person, or inanimate such as a desk, floor or a magnet. The agent for the force of gravity is Earth's mass. The ‘agent’ initiates or causes the force to happen. agent

For the purpose of developing force diagrams for problem analysis, all forces will be categorized as either contact or field forces. Contact forces are all forces that result from the contact between the system and its surroundings at the systems boundaries. Examples of contact forces are static and kinetic friction, tension forces and normal force.

Contact and Field Forces

Field forces or long-range forces result from the systems interaction with force fields such as magnetic, electric, or gravitational fields. A force has both magnitude and direction. Force is a vector quantity and therefore it can be represented with a free-body-diagram.

Circle the system and identify every place where the system touches the environment. It is at these places that contact forces are exerted. Identify the contact forces: FN f Fpush Identify any field forces: FG or W

Next replace the object by a dot. Each force is represented as an arrow that points in the correct direction. The tail of the force vector is always on the particle.

FN FG

FN FG

FN FF FG

FT FG

FT1 FT2 FG

FN FF FG

FN FT FG

FN1 FN2 FG

FN FA θ FF FG

FT FG

FG

FD FG FG

System of Interest f - All forces opposing the motion System 1: Acceleration of the professor and the cart System 2: Force the professor exerts on the cart