Warm Up Ch. 9 & 101. What is the relationship between period and

frequency? (define and include formulas)2. If an object rotates at 0.5 Hz. What is the

period of spin?3. Identify the linear speed of an object that is 2

m from the center of its spin and makes 1.9 rotations per second.

4. Calculate the tension in a 3 m string that whirls a 1.5 kg object at 2.5 m/s

Warm Up Ch. 9 & 101. What is the relationship between period and

frequency? (define and include formulas) T= 1/f and f= 1/T

2. If an object rotates at 0.5 Hz. What is the period of spin? T = 1 / 0.5 s-1 = 2 sec

3. Identify the linear speed of an object that is 2 m from the center of its spin and makes 1.9 rotations per second.

V= 2r/T = 22/0.53 s = 23.7 m/s4. Calculate the tension in a 3 m string that whirls a

1.5 kg object at 2.5 m/sF= mv2/r = (1.5 kg)(2.5 m/s)2 / 3m = 3.125 N

Quiz Next Class!!!

Ch. 11 Rotational Mechanics

Torque

• Produces rotation• Force is applied with leverage

Torque = Force x lever arm distance

** Note, we will be using Newtons for Force and meters for distance!!!

Can Torques Balance???

Problem Solving

Torque = Force x lever arm

• Calculate the Torque produced by a 23 N perpendicular force at the end of a 0.15 m long wrench.

Problem Solving

Torque = Force x lever arm

• Calculate the Torque produced by a 23 N perpendicular force at the end of a 0.15 m long wrench.

Torque = Force x lever arm

Torque = (23 N) (0.15 m)Torque = 3.45 Nm

Torque = Force x lever arm

• Calculate the individual torques produced by the students on the seesaw if the force produced for each mass is 125 N and the lever arm distance (L) across is 2 m.

Torque = Force x lever arm

• Calculate the individual torques produced by the students on the seesaw if the force produced for each mass is 125 N and the lever arm distance (L) across is 2 m.

Torque Left side:(125 N + 125 N)(2m) = 500 Nm Torque right side: (125 N)(2m) = 250 Nm

Rotational Inertia

• An object rotating about an axis tends to keep rotating about that axis

Remember Inertia is just a resistance to change.

In our lab activity before the break, which object rolled down the incline with a greater acceleration? Why?

In our lab activity before the break, which object rolled down the incline with a greater acceleration? Why?

• The object with the smallest rotational inertia. • The object with greater rotational inertia

required more time to get rolling and accelerating!!

Rotational Inertia (I) of different objects

Angular Momentum

• Product of rotational inertia and rotational velocity

• Angular momentum = I x

Can you guess what the Law of Conservation of Angular Momentum

says????

Can you guess what the Law of Conservation of Angular Momentum

says????

If no unbalanced external torque acts on a rotating system, the angular momentum of that system is constant.

Real life example of conserved angular momentum:

In class activity.