Although the principle of momentum conservation is a consequence of Newton's second and third laws of motion, as recognized by Newton himself,1 this principle is typically applied in analyzing collisions as if it is a separate concept of its own. This year I sought to integrate my treatment of collisions with my coverage of Newton's laws by asking students to calculate the effect on the motion of two particles due to the forces they exerted for a specified time interval on each other. For example, “A 50-kg crate slides across the ice at 3 m/s and collides with a 25-kg crate at rest. During the collision process the 50-kg crate exerts a 500 N time-averaged force on the 25 kg for 0.1 s. What are the accelerations of the crates during the collision, and what are their velocities after the collision? What are the momenta of the crates before and after collision?”

Topics
Newtonian mechanics, Education
1.
I. Newton, Principia Mathematica, 3rd ed., translated by I. Bernard Cohen and Anne Whitman, with assistance of Julia Budenz (University of California Press, Berkeley, 1999).
2.
Edward D. Lambe and John M. Fowler, The Particle Universe (Washington University, St. Louis, 1960), pp. 105–107.
3.
T. A.
Walkiewicz
and
N. E.
Newby
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Linear Collisions
,”
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4.
Gordon P.
Ramsey
, “
A simplified approach to collision processes
,”
Am. J. Phys.
65
,
384
–
389
(May
1997
).
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Crossref
Search ADS
 
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© 2003 American Association of Physics Teachers.
2003
American Association of Physics Teachers
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