Forces and free-body diagrams

Non-contact forces

Forces acting between two objects that are not in physical contact with each other

Weight Fg

The gravitational force the Earth exerts on any object on or near its surface

Normal force Fn

The perpendicular force exerted by a surface on an object in contact with it

Frictional force Ff

The force that opposes the motion of an object

Frictional force due to a surface

Frictional force that act parallel to the surface with which the object is in contact

Static frictional force Ffs

The frictional force of an object at rest on a surface which must be overcome in order to make that object move

Maximum static friction Ffsmax

Frictional force which is equal to the maximum force that can be applied to an object without the object moving

Kinetic frictional force Ffk

The frictional force that an object experiences while sliding on a surface

Free-body diagram

A diagram where the object of interest is drawn as a dot and all forces acting on it drawn as arrows pointing away from the dot. Must be labelled

Contact forces

Forces acting between two objects that are physically touching each other