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Air Track - Newton's Second Law


To demonstrate F = ma.


Air track, photocell gate timer system, gliders of mass M and 2M, small masses with audiotape frictionless cord, as photographed.


distance between them. You must therefore hold the glider so that the tab interrupts the photocell light beam immediately when

Setup Time

5 min.




A small mass hanging over a frictionless pulley provides the constant force which accelerates the glider between gates A and B. Using the photogate timing system, the time for the glider to travel from A to B can be measured, or the velocities of the glider at positions A and B can be measured using the 5 cm tab mounted on the glider. The accelerating force can be varied by adding additional masses, or gliders of mass M, 2M, and 3M (2M + M) can be used. A careful measurement yields a result good to a few percent.


Information Sheet. B. Saelman, Some Notes on Newton's Second Law of Motion, AJP 25, 584-585 (1957). ◙James L. Anderson, Newton's first two laws of motion are not definitions, AJP 58, 1192-1195 (1990).