Question

In the lab, you performed a trial where the fan was turned off partway through the run. What did the graph for this trial look like? How does the slope of the graph change, and why?

Answer 1

You should see a continuous curve with a clear kink at the moment the fan was switched off — two different slope regimes before and after that time.

- While the fan was on: the plot has a steeper slope (larger magnitude). That reflects the larger rate of change produced by the fan (greater convective heat transfer if you were measuring temperature, greater thrust/airflow if you were measuring velocity or flow rate).
- When the fan was turned off: the slope becomes noticeably smaller (less steep). The rate of change drops because the fan’s contribution (extra cooling, thrust, or airflow) is removed and the system is then governed by the slower processes left (natural convection/ conduction, drag/friction, or inertia).

In other words the graph is continuous but not smooth at the switching time: slope (dy/dt) decreases abruptly when the fan is turned off. You can quantify this by computing Δy/Δt before and after the switch and comparing the magnitudes.