Α is the angular acceleration associated with the rotational motion of the particle P. W is the angular velocity associated with the rotational motion of the particle P. The figure below shows a particle P traveling around a circle of radius R, with fixed center at O. Velocity And Acceleration Of A Particle Traveling Around A Circle The angular acceleration α (t) is given by Thus, the angular velocity w(t) is given by If the angular acceleration is known as a function of time, we can use Calculus to find the angular position, angular displacement, and angular velocity, in the same manner as before.Īlternatively, if we are given the angular position θ(t) as a function of time, we determine the angular velocity by differentiating θ(t) once, and we determine the angular acceleration by differentiating θ(t) twice.įor example, let's say the angular position θ(t) of a particle is given by This gives usĮquations (1), (2), (3), and (4) fully describe the rotational motion of rigid bodies (or particles) rotating about a fixed axis, where angular acceleration α is constant.įor the cases where angular acceleration is not constant, new expressions have to be derived for the angular position, angular displacement, and angular velocity. If we wish to find an equation that doesn’t involve time t we can combine equations (2) and (3) to eliminate time as a variable. As a resultĪngular displacement is defined as Δ θ = θ 2− θ 1. Substituting these two initial conditions into the above two equations we getįor convenience, set θ(t) = θ 2 and w(t) = w 2. The initial conditions are:Īt time t = 0 the angular position is θ 1.Īt time t = 0 the angular velocity is w 1. The constants C 1 and C 2 are determined by the initial conditions at time t = 0. Where θ(t) is the angular position and C 2 is a constant. Integrate the above equation with respect to time, to obtain angular position. Where w(t) is the angular velocity and C 1 is a constant. Integrate the above equation with respect to time, to obtain angular velocity. Where α is the angular acceleration, which we define as constant. The derivations that follow are of the exact same form as the equations derived for rectilinear motion, with constant acceleration. The easiest way to derive these equations is by using Calculus. With angular acceleration as constant we can derive equations for the angular position, angular displacement, and angular velocity of a rigid body experiencing rotation about a fixed axis. These are important quantities to consider when evaluating the rotational kinematics of a problem.Ī common assumption, which applies to numerous problems involving rotation about a fixed axis, is that angular acceleration is constant. Given the angular position of the rigid body we can calculate the angular displacement, angular velocity, and angular acceleration. This angle can be measured in any unit one desires, such as radians, or degrees.Įvery point in the rigid body rotates by the same angle θ(t). In the figure, the angle θ(t) is defined as the angular position of the body, as a function of time t. This type of motion occurs in a plane perpendicular to the axis of rotation. The figure below illustrates rotational motion of a rigid body about a fixed axis at point O. It is very common to analyze problems that involve this type of rotation – for example, a wheel. Rotation about a fixed axis is a special case of rotational motion. Rotational Motion Rotation About A Fixed Axis
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