The Second Law In Rotation

I. The second law:

1.

　

Step

Diameter (cm)

r Radius (cm)

smallest

 　 　

Middle

 　 　

largest

 　 　

2. Print out one sample dada. (see back)

And comment on the graph …..

3. Set 1 Use the medium step.

Remember that the hanger itself is 5 grams.

r : radius of step pully

　

α: angular acceleration

g = 980 cm/s2

(I+mr2 )meas = mgr/α

Imeas = (I+mr2 )meas - mr2

m

(g)

r

(cm)

α

(rad/s2)

mgr

(g-cm2/s2)

mr2

(g- cm2)

(I+mr2 )meas

(g-cm2)

Imeas

(g-cm2)

20

 　 　 　 　 　 　

40

 　 　 　 　 　 　

60

 　 　 　 　 　 　

80

 　 　 　 　 　 　

100

 　 　 　 　 　 　
　

Average

 　

Answer questions:

  1. How big is the “ mr2 ” ? Is it neglible?
  2. Which data might be most effected by friction in the system?
    How would the friction change the measuredαand I ?

Print out the graph “mgr vs.α”. and find the slope.

4. Set 2 Use 3 different steps

m

(g)

r

(cm)

α

(rad/s2)

mgr

(g-cm2/s2)

mr2

(g- cm2)

(I+mr2 )meas

(g-cm2)

Imeas

(g-cm2)

100

 　 　 　 　 　 　

100

 　 　 　 　 　 　

100

 　 　 　 　 　 　

　

　

II. Moments of Inertial :

1. Use the medium step.

Object

m

(g)

r

(cm)

α

(rad/s2)

mgr

(g-cm2/s2)

mr2

(g- cm2)

(I+mr2 )meas

(g-cm2)

Imeas

(g-cm2)

Platter

100

 　 　 　 　 　 　

Platter+Ring

100

 　 　 　 　 　 　

Platter+Bar

100

 　 　 　 　 　 　

Calculate Iring and Ibar .

2.

　

Object

Mass (grams)

Dimensions (cm)

Platter

 　 R =

Ring

 　 R1= R2=

Bar

 　 A = B =

　

　

Object

I - Theory

(gram-cm2)

I - Measured

(gram-cm2)

%error

Ring

=

 　 　

=

 　 　

Bar

　 　

　

　

Answer the questions in procedure 8.