how is precession of a heavy top possible?
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How is Precession of a Heavy Top Possible?. Svilen Kostov and Daniel Hammer Department of Geology and Physics Georgia Southwestern State University. How is Precession of a Heavy Top Possible?. - PowerPoint PPT PresentationTRANSCRIPT
How is Precession of a Heavy Top Possible?
Svilen Kostov and Daniel HammerDepartment of Geology and Physics
Georgia Southwestern State University
How is Precession of a Heavy Top Possible?
Svilen Kostov and Daniel HammerDepartment of Geology and Physics
Georgia Southwestern State University
Introductory physics is too simple; our task is to make it more complicated (a paraphrase of Søren Kierkegaard)
1. The heavy top-yesterday and today
‘Theorie des Kreisels’
Euler anglesand Euler-Lagrangeequations
the ‘tippy top’
a future physicist
3. Precession?Q. What will the spinning gyroscope do after it is released from rest?
A. Many students predict this.
B. Most introductory texts prove this.
3. Precession?Q. What will the spinning gyroscope do after it is released from rest?
A. Many students predict this.
B. Most introductory texts prove this. (where did the vertical angular momentum come from?)
4. Precession and nutationA. Both!
“It has to go down a bit in order to go around” R. Feynman in ‘The Feynman Lectures on Physics, vol. 1’
5. A PASCO based lab
1.
2. 3.
4.
5.
1. Demonstration gyroscope (PASCO) with two digital rotational sensors
2.Mini drill (DREMEL) with rubber head to accelerate disk to target rpm values
3.Digital stroboscope (EXTEC Instruments) to measure initial spin rate by observing aliasing pattern of spot on disk
4.Supporting stands
5.Data acquisition device (‘Explorer’, PASCO)
6. The data
φ (rad)
θ (r
ad)
7. Theory/model
• Conservation of momentum
0L L 3
mgr
1 3
21
mgr
Lo
LΔL
Δθ
(“Steady precession”, from your favorite text)
(From diagram; for small angles)
(Keeping track of directions through moments of inertia)
8. Fit to the model
9. Summary• The standard derivation of precession velocity of a heavy
spinning top released from rest is incomplete (the external torque cannot start the precession)
• The above top necessarily “falls”; i.e. dips from the horizontal, since angular momentum in the y-z plane is conserved (the external torque at t= 0 is perpendicular to that plane)
• The dip angle is simply related to the precession velocity; both can be measured accurately using teaching quality equipment
• The experiment and analysis described in this work can easily be incorporated into a junior type lab for the physics and engineering major
10. References• R. A. Serway, Physics for Scientists and Engineers, 6th. ed.
(Thomson/Brooks/Cole 2009), p. 350• R. Feynman, R. Leighton and M. Sands, The Feynman Lectures in Physics
vol.1,(CIT 1963), p. 20-7• M. S. Tiersten et al. “Propagation of a Feynman error on real and inertial
forces in rotating systems”, Am. J. Phys. 66 (1998)• Tuleja et al. “Feynman’s Wobbling Plate,” Am. J. Phys. 75, 240 (2007)• Butikov E., “Forced Precession of a Gyroscope “ 2006
http://www.ifmo.ru/butikov/Applets/Gyroscope.html • S. Kostov and D. Hammer, “A Lab for Exploring the Precession and
Nutation of a Gyroscope”, AAPT Advanced Labs, www.compadre.org/advlabs