Sports whistle

Whistle drawing by Sage w/ Design.

It's hard to imagine a coach without a whistle.

Metal can produce a whistling noise because of air pressure.

Whistles are commonly made from brass or nickel-plated brass because they are rust resistant to saliva. Compare this to horned instruments made of brass. It also sounds better than other materials.

Two materials are needed to make a whistle: a brass sheet and synthetic cork.

You don't actually need the ball for the whistle to make noise. The synthetic cork gives the whistle a sharp shrill which makes it easier to hear. The ball was traditionally cork because it's lightweight and blocks airflow well. But moisture would get trapped in the cork and cause it to jam and grow mold. Synthetic cork doesn't hold moisture so it's the new standard. The airflow being disrupted by the ball causes a higher pitched sound and the rattling shrill. Sound frequency is dependent on the whistle's length.

Early whistles were wooden. The first metal whistles were invented in the 1880s for the London police force. Before whistles, officers and coaches used hand rattles to get people's attention.

Whistles are simple and effective. There's good reason why there haven't been dramatic changes to their designs since the early 20th Century.