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Discussion

Consider the animation below of the motion for particle P:

• For all time, P moves with a positive x-component and a negative y-component of both velocity and acceleration. Why? Can you see this in the animation?
• As we will see in the next class period when we talk about the "path description" of kinematics, the velocity of a point is always tangent to the path of the point, and the acceleration always points "inward" on the path of the point. Do you see this in the animation?

The components of velocity and acceleration of P are found directly from the time derivatives of the position components:

v_P = x_dot i + y_dot j
a_P = x_ddot i + y_ddot j

DISCUSSION
For the velocity analysis of this mechanism, it is recommended that you write down three vector velocity equations: 1) relating the motion of O and C; 2) the motion of B and C; and, 3) relating the motion of A and B. Solve the resulting scalar equations from these vector equations for the angular velocities of AB and of the disk.

For the acceleration analysis, repeat the above process, but now use the three acceleration equations. Solve the resulting scalar equations from these vector equations for the angular accelerations of AB and of the disk. Please note that the acceleration of the no-slip contact point is NOT zero. Please read this page from the lecture book for an explanation as to why C can have a non-zero component of acceleration in the direction normal to the surface on which it rolls..

For example, the velocity and acceleration equations for link AB are given by:
v_B = v_A + ω_AB x r_B/A
a_B = a_A + α_AB x r_B/A - ω_AB²*r_B/A