Rotational motion is all about spinning objects. We'll dive into the key variables that describe how things rotate, like , velocity, and acceleration. These concepts help us understand everything from spinning wheels to revolving doors.
We'll explore how rotational motion relates to linear motion and learn to calculate important values. Understanding these ideas is crucial for grasping the physics of rotating objects in our everyday world.
Rotational Motion Variables
Rotational variables in fixed-axis rotation
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(θ) measures the angle through which an object has rotated from a reference point (initial position) in radians (rad)
(ω) represents the rate of change of angular position with respect to time measured in radians per second () (speedometer reading)
(α) describes the rate of change of with respect to time measured in radians per second squared () (accelerating or decelerating a spinning wheel)
involves an object rotating about a fixed axis or pivot point (spinning top, revolving door) where all points on the object move in circular paths centered on the axis of rotation
is the change in angular position over time
Angular velocity vs tangential speed
() is the linear speed of a point on a rotating object (speed of a point on the rim of a spinning wheel)
relates tangential speed to angular velocity (ω) and the radial distance (r) from the axis of rotation to the point of interest
The direction of the tangential velocity is always perpendicular to the radius (tangent to the circular path)
is the acceleration of an object moving in a circular path directed toward the center of rotation
Angular velocity from position functions
Angular velocity is the first derivative of angular position with respect to time ω=dtdθ
If the angular position is given as a function of time, θ(t) (pendulum's angle as a function of time), the angular velocity can be found by differentiating the function
Computation of rotational kinematics
Angular velocity can be calculated using the relationship ω=dtdθ (calculating the angular velocity of a rotating fan)
is the first derivative of angular velocity with respect to time α=dtdω
If the angular velocity is given as a function of time, ω(t) (angular velocity of a spinning top over time), the angular acceleration can be found by differentiating the function
Average angular acceleration calculation
() is the change in angular velocity divided by the time interval over which the change occurs
ωf is the final angular velocity (final speed of a spinning wheel)
ωi is the initial angular velocity (initial speed of a spinning wheel)
tf is the final time
ti is the initial time
Instantaneous acceleration from velocity functions
is the first derivative of angular velocity with respect to time at a specific instant α=dtdω
If the angular velocity is given as a function of time, ω(t) (angular velocity of a rotating fan blade), the can be found by differentiating the function and evaluating it at the desired time (acceleration at a specific moment)
Rotational dynamics
is a measure of an object's resistance to rotational acceleration
is the rotational equivalent of force, causing angular acceleration
is the rotational analog of linear momentum, describing the tendency of a rotating object to maintain its rotation