BNG 202 – Biomechanics II. Lecture 14 – Rigid Body Kinematics. Instructor: Sudhir Khetan, Ph.D. Wednesday, May 1, 2013. Particle vs. rigid body mechanics. What is the difference between particle and rigid body mechanics? Rigid body – can be of any shape Block Disc/wheel Bar/member
move along paths equidistant
from a fixed plane
any single particle (pt)
in the body
Rigid-body (continuum of particles)
about fixed axis
types of motion
Simplified case of our relative motion of particles discussion – this situation same as cars driving side-by-side at same speed example
fixed in the body
Counterclockwise is positive!
angular velocity vector always perpindicular to plane of rotation!
Magnitude of ω vector = angular speed
Direction of ω vector 1) axis of rotation
2) clockwise or counterclockwise rotation
How can we relate ω & αto motion of a point on the body?
Axis of rotation
In solving problems, once know ω & α, we can get velocity and acceleration of any point on body!!!
(Or can relate the two types of motion if ω & α unknown )
When the gear rotates 20 revolutions, it achieves an angular velocity of ω = 30 rad/s, starting from rest. Determine its constant angular acceleration and the time required.
The disk is originally rotating at ω0 = 8 rad/s. If it is subjected to a constant angular acceleration of α = 6 rad/s2, determine the magnitudes of the velocity and the n and t components of acceleration of point A at the instant t = 0.5 s.