Final answer:
A crosspiece on top of a T-shaped chimney pipe helps prevent down drafts by utilizing Bernoulli's principle. The T-shape creates a region of low pressure on top of the crosspiece, causing air to move faster and draw up gases. This design is effective even with a slight breeze.
Step-by-step explanation:
On a chimney, a crosspiece on top of a T-shaped chimney pipe helps prevent down drafts by utilizing Bernoulli's principle.
According to Bernoulli's principle, when the speed of a fluid (in this case, air) increases, its pressure decreases.
The T-shape of the chimney pipe creates a region of low pressure on top of the crosspiece, causing air to move faster, creating a suction effect that draws up gases and prevents down drafts.
This design is effective even with a slight breeze.