**PURPOSE: **To illustrate the experimental basis for Newton's second law of motion.

**DESCRIPTION: **This experiment uses the two gates to determine the time interval for the glider to be accelerated over the distance between them. You must therefore hold the glider so that the tab interrupts the photocell light beam immediately when the glider is released. The constant accelerating force is provided by a small mass hanging over a pulley on a low-friction tape connected to the glider.

**Acceleration is proportional to force.** Measure t for accelerationg mass m1 = 10 g and m2 = 20 g. Then a2 / a1 = (t1 / t2)**2 = m2 / m1.

**Acceleration is inversely proportional to mass.** Measure t for glider masses of M1 and M2 with the same accelerating mass. Then a2 / a1 = (t1 / t2)**2 = M1 / M2.

**SUGGESTIONS: **

**REFERENCES: ** (PIRA 1G10.11)

**EQUIPMENT: **Air track with photocell gate setup, gliders of mass 225 grams and 450 grams, and accelerating masses of 10 grams and 20 grams with frictionless tape, as photographed.

**SETUP TIME: **5 min.