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Rotational Motion

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The central intent of this lab is to provide students with the opportunity to predict the behavior of rotating systems using their knowledge of rotational dynamics and then to check to see if the predictions are correct.

At each individual station, the students are provided with a gyroscope, a tippy top and a butterfly yo-yo.

  • Gyroscope: Here the students start the gyroscope spinning and orient it so that the axis of rotation is horizontal. They are then asked to apply a torque to the gyroscope and predict how the gyro will move in response.

  • Yo-yo: the students place it on a table so that the string leaves the axis of the yo-yo from a point on the axis between the table and the center of the yo-yo. Their goal is see what happens when the string is pulled at an angle and what happens to the motion when the angle changes. They will see that at certain angles the yo-yo will roll towards them, at other angles it will not roll at all and at some angles it will roll away from them. They are asked to explain why the yo-yo behaves in this manner.

  • Tippy Top: This is more of a novelty item that they can play with and try to explain its pedular motion

At the general station there are a rotating stool, some small barbell weights and a weighted bicycle wheel with handles.

  • Activity 1: A student sits on the rotating stool and holds the rotating bicycle wheel so that its axis of rotation is horizantal. The student predict what will happen when the axis of rotation is moved to the vertical plane.

  • Activity 2: A student sits on the stool with arms extended and holding small weights in each hand. He/she is then started spinning and asked to bring his hands in towards his/her body. The students are asked to predict what the think will happen when the arms are brought in and explain the behavior of the rotating system.

  • Activity 3: While the person is spinning in Activity 2, a stationary student uses a stopwatch to measure the angular velocity of the student before and after the rotating students brings the weights in toward his/her body. This data is used to estimate the percentage change in the moment of inertia of the person and the masses when he/she pulled in his/her hands.

The third major activity involves a merry-go-groud. In this part, the students area asked to:

  • Activity 1: Computes the average angular velocity, the average period of rotation and the angular translational veloity.

  • Activity 2: Devise a method to measure the instantaneous translational velocity and then explain why the merry-go-round slows down in terms of Newton's first law. They are also to estimate the magnitude of the deceleartion

  • Activity 3: Next they rotate the merry-go-round using a metal bar. They are asked to note how much effort is needed to rotate the merry-go-round when the position of the push along the metal bar is varied from in near the axis of rotation to the far end of the poll. away from the axis of rotation.

  • Activity 4: They roll a soccer ball across the rotating merry-go-round to see how it moves. They then are asked to expain this observation.

  • Activity 5: They hang a string with a wieight attached to the other end from a ring stand and note how it hangs when the merry-go-round is at rest and when it is in motion.

  • Activity 6: The students place weights at various places around the merry-go-round and investigate how the position of the weights effect the forces needed to rotate the apparatus.

Course Level

Student Handouts


Number of set-ups available:

Per lab station:

1 tippy top
1 butterfly yo-yo
1 giant gyroscope/stand
1 string (~ 1 meter in length)
1 ball of string
1 gyroscope spinner

General class supplies:

1 rotating base
1 stoop for rotating base
2 bar bells - (5 lbs each)
2 bar bells - (3 lbs each)
1 weighted bicycle in a wooden frame
1 rotating wheel in a wooden frame
1 weighted bicycle wheel with handles and a rope attached
2 1000 kg hooked masses
miscellaneous assortment of tops

Merry-go-round station:

1 merry-go-round
1 soccer ball
2 stopwatches
1 roll of duct tape
1 meter stick
1 ball of string
1 tennis ball
2 500 gm hooked masses
1 bathroom scale

individual station
Individual Stations

class equipment
Genearl Class Supplies

Merry-Go-Round Apparatus

(Number of setups: 10)


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