nature and types of forces

addition of vectors

 space and free body diagrams

 resultants and equilibrants

If a system of forces is acting then they will have some net effect that is determined by their magnitudes and directions. If you add vectors together as outlined above you will discover that comprises the resultant, this is an imaginary vector that could replace all the individual vectors acting yet has the same effect. For example if a girl walks 1 km north then 1 km east, her position will be 1.4 km north east. She will end up in the same position if she walks 1 km north then 1 km east or if she simply walks 1.4 km north east. This last vector would represent the resultant of the last two.

An equilibrant may be defined as the force that will balance all other forces and place the system in equilibrium. Equilibrium is a condition where all the forces are balanced; thus there will be no resultant. The equilibrant has the same magnitude and direction as the resultant but it has the opposite sense.

principle of transmissibility of forces

three force rule for equilibrium

moments of a force

force/couple systems

equilibrium of concurrent coplanar forces