The speed at which an object breaks the sound barrier depends on many conditions, including weather and altitude. In dry air at 20 °C (68 °F), the speed of sound is approximately 343 meters per second (about 767 mph, 1234 km/h or 1,125 ft/s) . This is the speed at which sound travels and is known as the sound barrier. When an object approaches the speed of sound, it experiences a sudden increase in aerodynamic drag, which makes it difficult to continue accelerating. When an object exceeds the speed of sound, it creates a shock wave known as a "sonic boom".

The first pilot to officially break the sound barrier was Chuck Yeager in 1947 in the Bell X-1 Glamorous Glennis. He passed Mach 1, which is the point at which an aircraft equals and surpasses the speed of sound. The speed at which he broke the sound barrier was 1,127 kilometers (700 miles) per hour (Mach 1.06) . On 21 August 1961, a Douglas DC-8 broke the sound barrier at Mach 1.012, or 1,240 km/h (776.2 mph), while in a controlled dive through 41,088 feet (12,510 m) .