1. Relative Velocity

2. Relative Velocity: Equations written to relate motion to a frame of reference.
Motion that depends on velocity of an observer.
Motion relative to a frame of reference.

3. Relative Velocity: Equations written to relate motion to a frame of reference.
Motion that depends on velocity of an observer.
Motion relative to a frame of reference.
How fast are you moving as you sit in your seat????

4. What is this guy’s velocity?
He travels 4 meters in 2 seconds going east.

5. What is this guy’s velocity?
1 Compared to the ground?
2 What velocity does the earth spin at?
3 What velocity do we revolve around the sun?

6. INERTIAL!!!!!!!! What is this guy’s velocity?
So what is his frame of reference?
INERTIAL!!!!!!!!

7. Relative Velocity
What about now?
(for ground based observer) 7

8. What about now?
(for ground based observer)

9. Frame of reference A coordinate system from which all measurements are made.
Definition – a coordinate system within which objects, positions, and velocities are measured.
MUST PICK AN ORIGIN before you find speed and velocity.

10. Frame of reference
If two frames of reference are moving with constant velocity relative to each other, the objects appear to move with their own velocity and the frame’s velocity added together (remember that velocities are vectors).

11. Adding velocites. 20.4 m/s @ 79° east of north
Remember – Velocities are vectors.
Question – a “wing walker” is walking across the wings
of an airplane.
The airplanes velocity
is 20 m/s North.
His velocity is 4 m/s East.
What is his apparent
velocity to someone on the
ground?
° east of north

12. An airplane drops a care package
An airplane drops a care package. Describe the path taken by the care package as seen from the airplane’s frame of reference. What about from the ground’s frame of reference? If the airplane is speeding up with a constant acceleration, what would the package seem to do?

13. Falling Care Package
The airplane is moving horizontally with a constant velocity of
+115 m/s at an altitude of 1050 m.
Describe the motion of the package from the ground’s frame
of reference.

14. Falling Care Package
Describe the motion of the package from the airplanes frame
of reference.

15. Relative Velocity Crossing a River
The engine of a boat drives it across a river that is 1800 m wide.
The velocity of the boat relative to the water is 4.0 m/s directed
perpendicular to the current. The velocity of the water relative
to the shore is 2.0 m/s.
(a) What is the velocity of the
boat relative to the shore?
(b) How long does it take for
the boat to cross the river?
(c) How far downstream does the
boat come to ground? 15

16. Relative Velocity What do these subscripts means?
BS = Boat relative to Shore
BW = Boat relative to Water
WS = Water relative to Shore 16

17. Relative Velocity
θ = Cos-1 ( X / H)
Cos-1 (2 / 4.5) = 63o 17

18. Relative Velocity 18

19. Last comments on relative motion
Back to my first question about I’m walking.
What is the correct frame of reference?
Ground, center of earth, center of sun?
How do I test to find out?

20. Last comments on relative motion
There is no experiment you can perform to
determine (there is no way to tell) what frame
of reference you are in.
So, there is no “correct” frame of reference. All
are equally valid.
However, we usually pick
the one that makes the math
easiest to work.
INERTIAL!!!!!!!!