Relative Velocity in One Dimension

1
Relative Velocity(in One Dimension)

• How fast?
• It all depends on who you ask!!

2
Relative Velocity

• Velocity is a vector quantity
• How it is measured depends on the frame of
  reference
• The same motion can be described differently,
  based on the frame of reference

3
Frame of Reference

• When making measurements of the physical world, a
  reference point and directional system must be
  chosen
• All measurements are made from this reference
  point and within this directional system
• This frame of reference does not always have to
  be stationary

4
Motions Observed from Different Frames of
Reference
5
Frame of Reference Example 1Calculating
Velocities
6
Relative Velocity Problems

• A fish is swimming in the water at 2 m/s. The
  current is moving in the same direction as the
  fish at 1.5 m/s. What is the velocity of the
  fish as seen by a person sitting on the dock?
• What is the velocity of the fish as seen by
  person sitting in a row boat that is floating
  with the current?

7
Relative Velocity Problems

• What is the velocity of the fish as seen by a
  person in a motor boat that is traveling in the
  same direction as the current, but can move on
  its own at 15 m/s?

8
Relative Velocity Problems

• A fish is swimming in the water at 2 m/s. The
  fish is swimming against a current moving at 1.5
  m/s. What is the velocity of the fish as seen by
  a person sitting on the dock?
• What is the velocity of the fish as seen by
  person sitting in a row boat that is floating
  with the current?

9
Falling ObjectComparing Frames of Reference

• What the pilot sees

• What an outside observer sees

10
Falling ObjectComparing Frames of Reference
11
Evaluating Relative Velocity
A

• Assuming the cars move with constant velocity
• Sketch a position vs. time Graph for Car A
• Sketch a velocity vs. time graph for Car A

12
Evaluating Relative Velocity
A

• Assuming the cars move with constant velocity
• Sketch a position vs. time Graph for Car A
• Sketch a velocity vs. time graph for Car A

13
Evaluating Relative Velocity
A

• Assuming the cars move with constant velocity
• Sketch a position vs. time Graph for Car A
• Sketch a velocity vs. time graph for Car A

14
Evaluating Relative Velocity
A

• Assuming the cars move with constant velocity
• Sketch a position vs. time Graph for Car A
• Sketch a velocity vs. time graph for Car A