3.3

Relative Velocities

Student Notes

The river in this simulation is initially not moving. Run the simulation to see the boat move across the water. You are viewing the motion from the perspective of the shore.
The boat's velocity is given relative to the water. Like any boat, this one is carried with the water if it is in motion.
Now give the water some motion to the right by setting its velocity to 2 m/s. Now how will the boat move, as viewed from your perspective on shore? Make a prediction and run the simulation.
Even though the water is moving to the right, you can get the boat to move directly across the river. What special velocity must you choose to accomplish this? Set the boat's velocity appropriately, and use the simulation to see if you're right. Remember that the boat's velocity is given with respect to the water.
What factors determine the time it takes for the boat to reach the far shore?

Self-test

Just like a real boat, the boat in this simulation is limited to a maximum speed with respect to the water. How can you minimize the time needed to get to the far shore at any point? How can you minimize the time needed to get to a point directly across river from the starting point? Make these two predictions and use the simulation to check your answers.

Copyright © 2006 John Wiley & Sons, Inc. All rights reserved.