Relative Motion
Interactive simulation — adjust parameters and watch the visualization update in real time.
Live graphs
How it works
The water moves with the river; the boat has a velocity relative to the water. The velocity seen from the shore (ground) is the vector sum of the river’s flow and the boat’s velocity through the water. Aiming straight across is not enough when the river flows — you drift downstream unless you point partly upstream.
Key equations
vrel = (vb sin θ, vbcos θ) (θ from straight-across toward downstream)
vground = (vriver + vb sin θ, vb cos θ)