ch09 - Chapter 9 Rotational Dynamics 9.1 The Action of...

Chapter 9
Rotational Dynamics

9.1 The Action of Forces and Torques on Rigid Objects
According to Newton’s second law, a net force causes an
object to have an acceleration.
What causes an object to have an angular acceleration ?

9.1 The Action of Forces and Torques on Rigid Objects

9.1 The Action of Forces and Torques on Rigid Objects
DEFINITION OF TORQUE
Magnitude of Torque = (Magnitude of the force) x (Lever arm)
 F  
Direction: The torque is positive when the force tends to produce a
counterclockwise rotation about the axis.
SI Unit of Torque: newton x meter (N·m)

9.2 Rigid Objects in Equilibrium
If a rigid body is in equilibrium, neither its linear motion nor its
rotational motion changes.
0 

x
F

 0
y
F

 0 
0  
y x
a a
0  

9.2 Rigid Objects in Equilibrium
EQUILIBRIUM OF A RIGID BODY
A rigid body is in equilibrium if it has zero translational
acceleration and zero angular acceleration. In equilibrium,
the sum of the externally applied forces is zero, and the
sum of the externally applied torques is zero.