Free body diagrams

Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

There are two types of forces field forces can exist between objects, even in the absence of physical contact between two objects. For example, gravity or the electromagnetic force. contact forces arise when one object touches another.

Special Forces

Weight – Fg Field force Magnitude of the force of gravity on an object. Acts towards the center of the Earth (usually that’s down in the case of something near the surface of the Earth) Fg

Normal Force - FN Contact force Exerted by a surface on an object Acts in a direction perpendicular to the surface of contact FN

Friction – Ffr, fk, fs Contact force Also exerted by a surface on an object Acts in a direction parallel to the surface of contact opposite the relative direction of motion Ffr

Tension – FT Contact force Generated when a string is attached to a body and pulled taut Acts away from the body along the string at the point of attachment FT

Force Applied - Fa Usually contact force Generic force when you’re pushing or pulling an object. Make sure that the arrow originates at the point of application of the force and goes away from the object. Ffr

Steps to drawing a free body diagram: Identify the object of interest. Draw the object by itself as a simple box or simplified outline its shape. Consider field forces and contact forces. For each force acting on the object, draw an arrow. The arrow should: be proportional in length to the magnitude of the force. begin at the point of application of the force. be pointed away from the object in the direction the force is acting. be labeled with appropriate variable