__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.