Interactive Lecture Demonstration 10 – Merry Go
Round
The Merry Go Round in this
demonstration consists of a rotating stool on which a student will sit. The
student will hold the center of a long stick and will rotate at a constant
angular speed so that the stick moves in a horizontal circle. Horizontal
accelerometers are attached to the stick with their centers at positions 45 cm
and 90 cm from the center of the stick.
Since the acceleration of
objects moving in a circle at constant speed is directed toward the center of
the circle, the accelerometers will be oriented so that the plane of the cards
is radial (i.e., pointing to the center of the Merry Go Round).
- While the Merry Go Round
is rotating, measure the rotation period accurately by timing for at least 5
or 10 periods. You will need to decide on a reference point to tell when a
revolution is complete. Record your measurements below.
- How should the speeds of
the accelerometers located 45 cm from the center compare with the speeds of
those located 90 cm from the center ?
Calculate the two speeds.
- How should the
accelerations of the accelerometers located 45 cm from the center compare with
the accelerations of those located 90 cm from the center ?
Calculate the two accelerations.
- While the Merry Go Round
was rotating, observers measured the inclination angles of the BB's in the
horizontal accelerometers. Use the formula we derived for the accelerometers
to calculate the acceleration that the BB's experienced (take the average of
the angles measured by accelerometers on opposite sides of the circle).
Compare the accelerations measured by the accelerometers with your values
calculated from the radius and period of the motion.
- Predict the position of
the BB's if an accelerometer were placed at the center of the rotating Merry
Go Round. Explain.