Cumberland Times-News

Bob Doyle - Astronomy

November 16, 2013

Walking is natural, but not most efficient

What makes walking so natural and without much effort for most of us? Human walking can be related to the swing of a pendulum.

When at the end of its swing, a pendulum will stop, reverse direction, and reach its top speed in the lowest position. The pendulum “bob” will continue to the other side of the swing, stop and then reverse its motion. This back and forth motion is how our legs move.

The efficiency of walking depends on speed and gait (stride frequency and stride length). Human walking is more efficient than the walking of most mammals. For an average human, the walking speed for maximum efficiency is 4.26 feet per second.

The maximum speed for an average adult walking is 9.8 feet per second with a normal gait, more than twice as fast. Walking and running have the same efficiency at 7.5 feet per second.

The average speed of people in small villages of Greece and Crete is 2.6 feet per second. Contrast that with the average speed of walking in Brooklyn, Europe’s Prague and Athens from 4.9 to 5.9 feet per second.

At a typical walking speed, the force that your foot exerts on the ground is about three times your weight. If you take 1,000 steps per day, the total force on your feet will amount to several hundred tons!

All the numbers in this column are from the book, “All the Right Angles,” a book by Joel Levy and published in 2013 by Firefly. A column I wrote about baseball a few weeks ago included some insights from the above book.

Even more efficient than walking is riding a bicycle. Why are bicycles better?

First, bicycles have wheels, which roll smoothly over the ground in contrast to the choppy motion of our legs.

Second, bicycles rely on chain gears, which transmit force with high efficiency (over 98 per cent).

Third, most bicycles have different gears, allowing progress regardless of the gradient (slope). Bicycles take only 20 per cent as much energy as walking for the same distance.

A car can travel 279 feet on 100 calories of energy while a cyclist can travel three miles on the same 100 Calories. One pound is the amount of CO2 emissions saved each mile if traveled by bicycle instead of car.

Another popular pastime across most age groups is golfing. (Both of my parents were avid golfers but all I could hit were “air balls” (means I couldn’t hit the ball at all, probably feeling sorry for it).) The golf ball has a weight of only 1.6 ounce or 0.1 pound.

The impact of the golf club on the ball lasts 0.0005 seconds (one two thousandths of a second). The force acting on the ball during this brief time of contact is about 1,500 pounds.

During this time, the acceleration of the golf ball is over 14,000 G's (1 G is what we feel). The golf ball flies away at a speed of over 150 miles an hour.

A decent golf drive is 240 yards or 720 feet, farther than the longest ball hit in baseball (565 feet by Mickey Mantle in Washington’s Griffith Stadium in April 1953).

SKY SIGHTS AHEAD: This evening, the moon is full, rising about 15 minutes after sunset and setting as the sun rises tomorrow morning. The moon tonight appears near the Pleiades or Seven Sisters star cluster.

On Nov. 21, the moon will appear in the late evening eastern sky near the very bright planet Jupiter.

When the moon has shrunk to a narrow sliver in the last weekend of November, conditions will be best for spotting the tail of comet ISON in the 6 a.m. eastern dawn.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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