1. Lecture 15 – Relative Motion Analysis: Velocity
BNG 202 – Biomechanics II
Lecture 15 – Relative Motion Analysis: Velocity
Overall notes:
Control with UV exposure (cell spreading)
Instructor: Sudhir Khetan, Ph.D.
May 3, 2013

2. Types of rigid body motion
Kinematically
speaking…
Translation
Orientation of AB
constant
Rotation
All particles rotate
about fixed axis
General Plane Motion
(both)
Combination of both
types of motion B A B A B A B A
focus of today!

3. Kinematics of translation
Position
Velocity
Acceleration
True for all points in R.B. (follows particle kinematics) B A y rB rA x
A simpler way of saying this  rb/a = constant (since it is a rigid body)
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

4. Relative motion analysis: velocity
Transl. & Rotation
(General Plane Motion)
Position
Velocity (time deriv)
Let’s say motion of A is known
We would like to find motion of B
and (ω is rotation of member about A) A B
drA dθ y
rB/A
rB/A (new)
drA
drB/A
drB rA rB x
translation
rotation
why is this?
where

5. Review of cross products
See Chapter 4 of your statics text for full details or

6. Example Problem
If the block at C is moving downward at 4 ft/s, determine the angular velocity of bar AB at the instant shown. (F16-58, 2 rad/s)
Strategy: In beginning of the solution (“data” section should just be the sketch of the setup), what other information do we know about the components?

7. Example Problem
If rod AB slides along the horizontal slot with a velocity of 60 ft/s, determine the angular velocity of link BC at the instant shown. (F16-11, 48 rad/s)