Physics Photo of the Week
September
18, 2009
Horsepower
Student
Kate Zeigler is driving Warren Wilson's team of Belgian draft horses -
Curly Kate and Jenny. They are discing the Warren Wilson
vegatable garden in April, 2009 during the planting season.
During the developments of the industrial revolution 200 years ago,
James Watt performed experiments with horses pulling to lift loads with
hoists in order to measure the amount of work that a typical horse
could perform in a standard unit of time. He performed these
measurements in order to compare the work capability of his steam
engines with that of
horses. He found that a typical horse could produce 33,000 ft-lbs
of work per minute. In a quarry, for example, one horse attached
to a rope and pulley could lift a 100 pound load of ore a distance of
330 feet in one minute. This is also equivalent to lifting a 200
pound load a distance of 165 feet in the same minute. The steam
engines developed could lift 10-20 times the weights listed above in a
minute, hence the steam engines would be rated 10-20 horsepower.
In physics textbooks, the horsepower has been assigned the metric or SI
unit of 746 Watts or 746 Joules/sec. Thus a horse on a treadmill
geared to a generator should be able to power about seven 100 Watt
lamps,
assuming negligible friction.
Of course engine horsepower is very important in promoting high
performance cars. Engine power is usually measured with a device
called a "dynamometer". The dynamometer measures the torque by
means of a mechanical brake. The torque (foot-pounds) multiplied
by the shaft angular velocity (revolutions/min) yields the power in
foot-pounds/minute.
Even though engines can produce far more power than a horse, horses can
go many places that motor vehicles cannot. They don't get stuck
in snow or mud; they can pull loads up much steeper hills. Horses
also offer companionship to the farmers as the students on the horse
crew at Warren Wilson can readily attest.
"Plow Day" featuring farm draft horses had been scheduled at the Warren
Wilson College Farm this Saturday. However the event has been
canceled due to excessive rain. Watch for rescheduled times.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
