Students will sometimes ask why momentum and kinetic energy concepts are both necessary. When physics teachers demonstrate situations that require both an understanding of kinetic energy and momentum, a favorite is Newton’s cradle, or a comparable demonstration of two balls of equal mass hitting each other. However, in addition to the case of two balls of equal mass, if a ball hits another ball of three times the mass with equal speed, the results are also interesting, and, like the equal-mass demonstration, both kinetic energy and momentum are critical for understanding the motion.
References
1.
Harvey B.
Lemon
, “An almost forgotten case of elastic impact
,” Am. J. Phys.
3
, 36
(Jan.
1935
)2.
For example, they are sold at McMaster Carr, http://www.mcmaster.com/#standard-steel-balls/=u6kebk.
3.
View the videos at
TPT Online
, https://doi.org/10.1119/1.5028235 under the Supplemental tab.© 2018 American Association of Physics Teachers.
2018
American Association of Physics Teachers
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