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

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!

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

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

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

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?

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)