Tanks and Mixing

In, out, and the approach to balance

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Rate of change = rate in − rate out; outflow carries the current concentration.
• The solution approaches balance exponentially, with time constant (volume ÷ flow).
• After one time constant 63% of the way; after about five, essentially there.

Steps

1. Salt flowing in
2. Building the equation
3. Fill it fast enough
4. One time constant
5. A steady drip
6. Cleaning a lake