Net force is the product of mass and acceleration. The unit of force is newtons (N).

f = m × a.

The mass of an object is absolute – it is constant for a specific object or particle. However, the magnitude of weight is variable; it depends on gravitational field strength (location). Weight is the force acting upon an object due to gravity. 

W = m × g

The weight component of an object parallel to the slope is given by sinθ; the component perpendicular to the slope is given by mgCosθ.

Free body diagrams can be used to isolate all the forces acting on a particular object.

Weight The gravitational force acting on an object through its centre of mass 
Friction The force that arises when two surfaces rub against each other
Drag The resistive force on an object travelling through a fluid (the same as friction)
Tension The force within a stretched cable or rope
Upthrust An upward buoyancy force acting on an object when it is in a fluid
Normal contact force A force arising when one object rests against another,

equal to the component of the object’s weight parallel to the slope.

Each force vector is represented by an arrow labelled with the force it represents; each arrow is drawn to the same scale.