Trumpets on a Train

Plate 89 speaks for itself: “The note changed as they passed.”

The Physics

Buys Ballot put musicians on a train near Utrecht to test Doppler's prediction. Listeners heard the note sharpen as the train approached and drop once it passed.

f′ = f c / (c − v_s)

• f′: heard frequency, Hz
• f: emitted frequency, Hz
• c: speed of sound, m s⁻¹
• v_s: source speed toward the listener, m s⁻¹

1845: musicians on a train near Utrecht. Sharper as it came, flatter once it passed.

Sources

• C. H. D. Buys Ballot, Ann. Phys. 142, 321 (1845).

On the poster

Plate 089, “Trumpets on a Train”: the pixel-art plate with its slogan “The note changed as they passed.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.