Final answer:
The correct answer is D) Salad spinner. A salad spinner is used to visually demonstrate the Ekman spiral in the classroom, showing how the fluid layers rotate at different speeds due to friction, similar to ocean currents affected by the Coriolis effect.
Step-by-step explanation:
The question asks what common household item is used in the video to demonstrate the Ekman spiral. The correct answer is D) Salad spinner.
The Ekman spiral refers to a structure of currents or winds near a horizontal boundary in which the flow direction rotates as one moves away from the boundary. The salad spinner is used in demonstrations to show how the Ekman transport works due to the effect of friction and the Coriolis force acting on the fluid within the spinner. As the spinner rotates, the interior fluid begins to spin, and due to friction, the layers of fluid at different depths move at different speeds, creating a spiral pattern akin to the Ekman spiral observed in oceans where currents at different depths move in different directions due to the Coriolis effect and friction.