Horsepower

It’s only been a few weeks since my partner’s beloved grandmother passed away.

She’d been known to all as “Granny” for 50 years and had reached the ripe old age of 108 with her faculties still totally intact.

Born in 1902 her life had spanned the terms of every Australian Prime Minister though she never involved herself with politics.

Having already received her telegram from the Queen and taken a ride on a Harley trike at 103 years of age, it did prove difficult to think of what sort of birthday present to buy someone who was turning 108.

Scratching for options, my partner came up with the idea of a ride on a miniature horse and sulky.  After all Granny had used this mode of transport for most of her childhood to get to school.

As well as the horse and cart, steam power was also certainly still in use during most of her early life.

As machines began to replace animals for labour it became necessary to calculate their power output to convince potential purchasers that the expense of mechanization was justified.

In 1782 James Watt devised a measurement which equated the power output of a draft horse to the power output of a machine.

Watt calculated that a draft horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute).

If the wheel was 12 feet in radius the horse travelled 2.4 × 2? × 12 feet in one minute. Watt estimated that the horse could pull with a force of 180 pounds.

So:

This was rounded to an even 33,000 ft·lbf/min and was equal to one horsepower.

Watt also showed that a pony could lift an average 220 lbf (0.98 kN) 100 ft (30 m) per minute over a four-hour working shift. Watt then judged a horse was 50% more powerful than a pony and thus still arrived at the 33,000 ft·lbf/min figure.

Whilst humans may be briefly capable of exertion of 1.2 horsepower, most of us are flat out producing 0.1 horsepower persistently and only one in a million of us will do that for as long as Granny did.

Horsepower

Power: The rate at which energy is generated and consumed.

Centenarians: According to a 2005 study, “They are people who don’t dwell on the past. They just get on with it, basically.  Traits common to the centenarians in the study were a sense of humor, a strong work ethic and an engaging personality.  They were doers. They were not people who spent a lot of time sitting around.”   From “100 years old: 24 Australian centenarians tell their stories”, by Tina Koch, Charmaine Power & Debbie Kralik (2005).

Safe motoring,

Doctor Clive Fraser

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    Medical Motoring is an online record of the articles written by Dr Clive Fraser and published in the Australian Medicine magazine by the Australian Medical Association.