Lesson 2.2: What is relative velocity?
Do Now: Find the center of mass when the objects are 20 m apart.
]-----------20 m—----------[
If two objects are in motion:
Center of mass can be used to define the origin of the moving frame of reference for the system.
The relative velocities of each object can be calculated with respect to center of mass reference frame.
Relative Velocity
How the velocity of one object appears different depending on where you are or how you're moving.
Depends of frame of reference.
Don’t forget direction!
vR = v1 - v2
Example 1:
What is the velocity of the center of mass?
What is the velocity of each object with respect to the velocity of the center of mass?
]-----------20 m—----------[
Example 1 cont.:
When will the two objects collide?
]-----------20 m—----------[
Example 2:
When the 10 km/hr bikes are 30 km apart, a bee begins flying from one wheel to the other at a steady speed of 30 km/hr. When it gets to the wheel it abruptly turns around and flies back to touch the first wheel, then turns around and keeps repeating the back-and-forth trip until the bikes meet, and squish!
How many kilometers did the bee travel in its total back-and forth trips?
30
Example 3:
Quick Check:
Jogging Jake runs along a train flatcar as shown in images A-D. From greatest to least, rank the velocity of Jake relative to a stationary observer on the ground.
Summary:
What is relative velocity?
Practice:
AP Classroom Reference Frames and Relative Motion