AH 1.3 Rotational Dynamics Flashcards
What is the moment of a force?
The moment of a force is the turning effect caused by an applied force acting at right angles to the radius of a rotation about an axis and is given by T = F x r, where T = torque (or moment of the force) in Nm F = applied force perpendicular to radius of rotation r = radius of rotation
An unbalanced Torque causes what in a rotating body?
Angular acceleration.
The angular acceleration caused by an unbalanced torque, depends on which property of the rotating body?
The moment of inertia.
The moment of inertia of a rotating body, depends on which two properties of that body?
Mass and average radius of mass.
What is the moment of inertia I of a point mass m describing uniform circular motion at a radius r from its axis of rotation?
I = mr2
State what is meant by the angular momentum of a rotating body.
The Angular Momentum of a rotating body is given by the equation
L = Iω
where
L = angular momentum (kg m2 s-1)
I = the moment of inertia (kg m2)
ω = angular velocity (rad s-1)
State the Law of conservation of angular momentum in words.
In the absence of external torques, the angular momentum of a rotating body is conserved.
State the Law of conservation of angular momentum as an equation
In the absence of external torques
I1ω1 = I2ω2
Where
I1 = total moment of inertia BEFORE the interaction
ω1= angular velcoity of system BEFORE the interaction
I2 = total moment of inertia AFTER the interaction
ω2= angular velcoity of system AFTER the interaction
What does the rotational kinetic energy of a rotating body depend on?
- Its moment of inertia, and
- It’s angular veocity
What is the equation for the rotational kinetic energy of a rotating body?
Ek(rot) = 1/2 Iω2
