The Science:

Gravity can be defined as the force of attraction by which bodies tend to fall towards the centre of the earth (Adams & Breslin, 2012, p. 1).  

In general, gravitational hazards arise when a potentially unstable or unsecured object is involved in a damaging impact due to the manner in which gravity causes the object to fall to a lower level if the instability is realised or the object is dropped (e.g. when a tool is dropped from a height, or a person trips and falls).

The damaging forces that might ensue when a fall is interrupted arise when the energy associated with the momentum of the falling mass is transformed into another form of energy, primarily through processes such as:  

• Absorption (e.g. the body is punctured, crushed, lacerated, shaken or knocked off balance); and 

• Deformation of the body posture against either natural stiffness or muscle effort (e.g. when a person attempts to arrest a falling object using muscle power)(Viner, 1991).

The magnitude of the forces associated with gravitational hazards is one of the key determinants of the risk of injury – the higher the forces the greater the risk.

The consideration of forces associated with (i.e. causing or resulting from) moving objects is referred to as kinetics.

Stationary objects that can fall have potential energy (PE). The magnitude of that energy (in joules) may be calculated as follows:

PE=mgh

where: m=object mass (kg), g=acceleration due to gravity (e.g. 9.8 m/s2 ) and h=starting height (metres) (Adams &Breslin, 2012, pp. 6-7.).