Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography

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Measurement
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video - The Atwood Machine

Purpose:

To illustrate Newton's Second Law.

Procedure:

DEMO VIDEO DOWNLOAD w/ sound / 854x480 / 5.69Mb/s / 114MB size

For m1 = m2 = 550g, the masses do not accelerate (ie. stay motionless or move at constant speed)
For m1 = 550g and m2 = 600g, the measured time it takes m2 to accelerate from rest and fall 1.5m is 2.79s.
For m1 = 550g and m2 = 650g, the measured time it takes m2 to accelerate from rest and fall 1.5m is 1.97s.

You must take into account the mass of the pulley Mp = 173g due to moment of inertia of the disk.

One can compute the acceleration from the height mass m2 falls: h = 1/2 at² and compare with g.

Hints:

If one assumes the pulley is massless, the calculated time it takes m2 to fall 1.5m is:

2.60s and 1.84s for m2 = 600g and 650g respectively

If one takes into account the pulley mass Mp = 173g, the calculated time it takes m2 to fall 1.5m is:

2.80s and 1.97s for m2 = 600g and 650g respectively

Equipment:

Timer
1 2-meter stick
Atwood machine with attached pulley
Weights