Where does fall collide?

Galileo Galilei set out the law of falling bodies in Discorsi e dimostrazioni matematiche intorno a due nuove scienze (1638), showing that a body falling freely, acted on by gravity alone, gains speed uniformly with time and covers distances in proportion to the square of the elapsed time, whatever its weight. Free fall is that idealised motion in which gravity is the only force acting, with air resistance and other influences set aside. Here the referent is a physical trajectory measured in metres and seconds, not a moral descent into sin or an older adult's unintended coming to rest on the ground.[1]

Unit

One body's motion under gravity alone, in metres and seconds

Recovery means

Not applicable

Measured by

Position and speed over time, by timing, tracking, or accelerometry; gravity near Earth is about 9.8 m/s^2

Sheldon's 1960 On the Natural History of Falls in Old Age documented how and why older people fall, and Tinetti, Speechley, and Ginter's 1988 Risk Factors for Falls among Elderly Persons Living in the Community established the epidemiological study of falls and their risk factors in later life. In geriatric medicine a fall is an unintentional coming to rest on the ground or a lower level, and it is a leading cause of injury, disability, and loss of independence in older adults. Here the referent is a discrete adverse health event counted per person over time, not the theological Fall of humanity or the physicist's idealised motion under gravity.[2][3]

Unit

One person's unintended coming to rest on the ground, counted per person-year

Recovery means

Managed by treating injuries and lowering future risk through balance, strength, and changes to the environment

Measured by

Counted as fall incidence and rate, with risk assessed by gait and balance tests and by history