ELI5 : why do buses make that “PFSSSST” sound when they stop?
In: Engineering
Many large vehicles have a system of brakes actuated by compressed air instead of hydraulic fluid or cables you would find in a lighter vehicle or passenger car.
Parking/emergency brakes on such vehicles are usually “normally closed”: to release the brake, air pressure must be applied to the brake. For these, a sudden release of air pressure will quickly activate that brake, but also will create a little bit of noise.
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