1. Key Points of the Lesson
Relative Motion
Key Points of the Lesson
Understand that objects move differently in different frames of reference
Using vectors and vector diagrams to represent and calculate relative motion

2. Frames of Reference All motion is relative!
All motion is measured with respect to (wrt) a particular frame of reference.
Frame of Reference: system for specifying the precise location of objects in space and time; background against which motion is measured
An object’s velocity measured in one reference frame can be completely different when it is measured from another reference frame.

3. Relative Velocities
Need to distinguish velocities as measured in different frames of reference.
Use subscripts using two letters:
Read as: velocity of (first letter) wrt (second letter)
vac = vab + vbc
Important: vab = -vba
Since velocity is a vector quantity, rules of vector addition and vector resolution apply

4. Relative Velocity – Example 1
You are walking backward in a bus at a rate of 1 m/s. Relative to the earth, the bus is moving forward at 19 m/s.
What is your velocity relative to the bus (and other passengers on the bus)?
What is your velocity relative to an observer on the side of the road?

5. Relative Velocity – Example 2
You are driving North at 55 mph. A driver in the Southbound lane approaches you at 45 mph.
What is your velocity relative to the other driver?
What is your velocity relative to an observer on the side of the road?

6. Relative Velocity – Example 3
An airplane is flying due east relative to still air at a speed of 320 km/h. There is a 65 km/h wind blowing toward the north, as measured by an observer on the ground. What is the velocity of the plane measured by the ground observer?