Laboratory 10
The Sweet Spot

MECH324
Dynamics of Machines


Name: __________________________Lab Sect. _______

Date: _______________


SHOW WORK WHERE SPACE IS GIVEN

EXPERIMENTAL

  1. Mass of bat, m:   ________(kg) (it should be 0.84 kg, unless a different bat is used)
     
  2. Distance from origin to center of rotation, COR:  ________(m)
     
  3. Length of bat, Lbat:  ________(m)
     
  4. Distance from origin to center of gravity, CG:  ________(m)
     
  5. Length of string 1, L1 (if applicable):  ________(m)
     
  6. Length of string 2, L2 (if applicable):  ________(m)
     
  7. Distance from pivot point to CG, LCG:  ________(m)
     
  8. Distance from pivot point to center of rotation, LCOR:  ________(m)
     
  9. Natural frequency of swinging bat in Hz, fo:  ________(Hz)
     
  10. Natural frequency of swinging bat in rad/sec, Ωo:  ________(rad/sec)
     
  11. Moment of inertia about the pendulum's pivot point, Io:


    Io=__________(kg*m2)
     
  12. Moment of inertia about the bat's center of gravity, ICG.


    ICG=__________(kg*m2)
     
  13. Moment of inertia about the bat's center of rotation, ICOR.


    ICOR=__________(kg*m2)
     
  14. Radius of gyration, k.


    k=__________(m)
     
  15. Distance from the CG to the center of percussion, lp.


    lp=_________(m)
     
  16. Distance from the handle to the sweet spot.


    sweet spot=_________(m)

 

THEORETICAL

Draw a model of the bat, TO SCALE, using AT LEAST 3 simple geometrical volumes.  Label:
- names of volumes (e.g., cylinder, conical frustum) with labels (e.g., "A", "B", etc)
- draw "negative" volumes as dotted lines
- dimensions of shapes (e.g., lengths, widths, radii)
- put a "+" at each center of gravity for individual shapes (use table to determine CGs)
- distances to each CG from origin
 







 
 












 
  1. Distance from origin to center of gravity, CG.





    CG:  ________(m)
     
  2. Label the CG (of the whole bat) on your model with a star.

     
  3. In the table below, list the moments of inertia for each volume in your model
     
    VOLUME LABELSMoment of Inertia, IGGMass, mDistance from Origin, dMoment of Inertia about Origin
    (IGG + md2)

     
        

     
        

     
        

     
        

     
        

     
        

     
        

     
        

  4. Moment of inertia about the bat's origin, IZZ.


    IZZ=__________(kg*m2)
     
  5. Moment of inertia about the bat's center of gravity, ICG.


    ICG=__________(kg*m2)
     
  6. Moment of inertia about the bat's center of rotation, ICOR.


    ICOR=__________(kg*m2)
     
  7. Radius of gyration, k.


    k=__________(m)
     
  8. Distance from the CG to the center of percussion, lp.


    lp=_________(m)
     
  9. Distance from the handle to the sweet spot.


    sweet spot=_________(m)

 

THE "REAL SWEET SPOT"

  1. Distance from the handle to the sweet spot.


    sweet spot=_________(m)
     
  2. Error of experimental sweet spot:  _________(%)
     
  3. Error of theoretical sweet spot:  _________(%)