Net external forces

The vector sum of all external forces acting on an object or system is called the net external force Fnet and is also represented as ΣF summation of forces . By Newton’s Second law of motion, the net force produces an acceleration on the body it acts on as long as its value is not zero.

As an example, consider the case in which a body is being pulled up by a lifting force and pulled down by its weight. The net force acting on that object is the vector sum of the lifting force and the weight.

Since the net force is a sum of vectors, calculating the net force often involves vector addition. Frequently (in the case where we have forces in more than one direction) the most convenient method of doing this is decomposing vectors along two different axes of a coordinate system and then adding the components along each axis separately. A useful tool that can be of assistance in this case is a free-body diagram.

Figure 1: Two forces applied to a body in the first image. Net force pointing downwards on the y-axis in the second image (ΣF=F_G-F_Lifting=10N).