Centre of Mass
Commonly know as Centre of Gravity
Often the "centre of mass", the point at which the mass of an object is effective, is referred to as an objects centre of gravity. This works in some fields however fields such as avaiation and astronomy use the term "centre of gravity" correctly to define the effective point source of gravitational force caused by a body. In these calculations you need to be able to differentiate between the centres of mass and gravity.
The centre of mass of an object is the point at which the mass of that object is effective. For a regular shaped piece of solid uniform material, that point is in the geometric centre, for example:
Determining the Centre of Mass
Most objects are not regular shaped or uniform material. This leave us with two options: calculation or practical determination.
A very simple method is to hang the object in question from a single point. Attach a plumb line to the hanging point and draw a line on the object along the plumb line. Hang the item from a different point, attach the plumb line to that point and draw another line. The centre of mass is at the point that the two lines intersect. If you need the centre of mass in three dimensions, turn the object 90° and repeat the steps above.
Calculation the Centre of Mass
The easiest way to calculate the centre of mass of a complex object is to split it into component parts of regular shapes. The properties of each shape are then combined summing the products of mass and centre of mass co-ordinates of each section and dividing the total by the total
Diagram of 'L' shape 10m tall 8m wide and 3m thick split into 10 x 3 and 5 x 3 and 1m deep.
The shaped above is made of a uniform material with a mass of 1kgm-3
Adujst the values below to recalculate the Centre of Mass