3.2.1 Dynamics

The mass of an object depends on the amount of matter it contains. The net/resultant force acting on an object will make it accelerate in that particular direction. The net force (F):

F = m a

Force is measured in newtons (N). A force of 1 newton will give a 1kg mass an acceleration of 1m s^-1 in the direction of the force.

The weight of an object on the surface of the Earth is the gravitational force acting on the object:

W = m g

The weight of an object can be calculated using a newtonmeter. These are calibrated to show the gravitational force acting on an object in newtons (e.g an object of mass 1kg will show a weight of 9.8N).


The easiest way to analyse the forces acting on an object is to draw free-body diagrams (these isolate all the forces acting on a particular object. Each force vector is represented by an arrow labelled with the force it represents, each arrow is drawn to the same scale (ie the longer the arrow the greater the force).

Tension, normal contact force, upthrust, and friction are all examples of forces that can be added to a free-body diagram.