Kinematic models are often very useful. The back and forth throw of a ball between two ice skaters may help us appreciate the meson exchange theory of Yukawa. If the skaters throw the balls at each other, they move backward, which is equivalent to a repulsive force between them. On the other hand, if they snatch the ball from each other, the result will be akin to an equivalent attractive force between them. Such illustrative models may help us understand advanced concepts.

1.
A.
Beiser
,
Concepts of Modern Physics
, 5th ed. (
Tata McGraw-Hill Publishing Company Ltd.
,
New Delhi
,
1995
), p.
410
.
2.
D.
Halliday
,
R.
Resnick
, and
J.
Walker
,
Fundamentals of Physics
, 8th ed. (
Wiley India (P) Ltd.
,
New Delhi
,
2008
), p.
461
.
3.
F. W.
Sears
,
M. W.
Zemansky
, and
H. D.
Young
,
College Physics
, 7th ed. (
Addison-Wesley Publishing Co.
,
New York
,
1990
), p.
523
.
4.
G. B.
Arfken
,
D. F.
Griffing
,
D. C.
Kelly
, and
J.
Priest
,
University Physics
, 2nd ed. (
Harcourt Brace Jovanovich Publishers
,
San Diego
,
1989
), p.
335
.
5.
Bernhard
Rothenstein
, “
Teaching the Doppler shift from a machine gun analogy
,”
Phys. Teach.
39
,
468
469
(
Nov.
2001
).
6.
R.
Serway
and
J. W.
Jewett
,
Physics for Scientists and Engineers
, 9th ed. (
Cengage Learning
), Example 17.4.
7.
S. M.
Torres
and
W. J.
Gonzalez-Espada
, “
Calculating g from acoustic Doppler data
,”
Phys. Teach.
44
,
536
539
(
Nov.
2006
).
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