The answer is (f): my heartbeat causes the scale to read slightly less than my weight W for a small interval of time each heartbeat, as seen in an mpeg video by clicking your mouse on the graph below. This video has been converted from standard NTSC into mpeg format while slowing down the motion by a factor of three so that the motion of the scale may be more easily observed.
This area of the physics of the human body is known as "ballistocardiography." Dr. John Cameron, Professor Emeritus at the University of Wisconsin Medical School, has provided a concise explanation of this phenomenon, which is well-known to physicians:
Additional information regarding this and other phenomena involving the physics of the human body can be obtained from the following references (obtained from John Cameron before his death):
(from John Cameron) A year before he died John Lenihan agreed to publish an updated version of his 1974 book "Human Engineering," which had been long out of print. He had agreed to the new title as being more descriptive. Unfortunately John died before he got a chance to update it. His widow gave me permission to publish a new revised edition under the new title. The only major revision was to the chapter on organ transplants. In 1973 organ transplants had a very poor success rate. Now thousands are done every year and a large fraction (over 90%) are alive a year later. The book is very readable but Medical Physics Publishing was not able to market it appropriately. I am not sure it was reviewed in TPT or other appropriate journals.
A more recent description of ballistocardiography is found in rhe web site The Ballistocardiogram, written by David M. Harrison, Dept. of Physics, Univ. of Toronto, in July 2003.
