How do the old men in the park master the secret of whipping at supersonic speeds?

Everyone must be familiar with whips. They can be used to drive livestock or as a weapon. Nowadays, whips have become a fitness tool and are called "snapping whips".

Source: Baidu Encyclopedia

Whip-snapping originated in Henan and is a popular fitness exercise. Bend your waist, close your shoulders, raise your arms, shake your wrists, and flick the tip of the whip. The whip will make a "snap" sound in the air, echoing all around. But did you know that every time the uncles whip, they can actually swing at supersonic speeds! ? How is this possible?

1. What is a sonic boom?

First, we need to know how a soft whip makes a sound in the air, which comes from a peculiar physical phenomenon - "sonic boom". "Sonic boom", if we look at it literally, means "sound explosion", but in fact, to understand "sonic boom", we must first know what "sound barrier" is.

The "sound barrier" can be simply understood as a barrier, but this barrier exists in the air and cannot be seen with the naked eye. Any object (including sound) will encounter a certain amount of resistance when propagating in the air. The faster the object moves, the greater the resistance will be, so that a barrier can be formed in the air, hindering the acceleration of the object.

Take airplanes as an example. When the speed of an airplane approaches the speed of sound, the drag suddenly increases, causing abnormal operation and spontaneous nose-diving. At the same time, the speed of the airplane cannot be increased any further. People once believed that the speed of sound was the speed limit of an airplane. After reaching the speed of sound, the airplane faces an invisible air barrier, so this phenomenon is called the "sound barrier" or "sound barrier."

Aircraft breaks the sound barrier

Source: pixabay

When we throw a stone into the water, circles of ripples will appear on the water surface with the point where the stone falls into the water as the center. The same is true for the propagation of sound. Sound propagates in the air in the form of waves. Any sound is centered on the sound source, and it expands in circles and spreads to the surrounding areas.

Sound wave demonstration

Source: Wikipedia

If the sound source is fixed and the sound transmission medium is completely uniform, the sound waves will be transmitted in the form of regular concentric circles, but when the sound source starts to move and accelerates, the sound waves around the sound source will present a cone-shaped stereo sound wave energy field. If the newly generated sound waves are superimposed on the previous sound waves, the sound will become louder.

If the scope of application is expanded to all waves (light waves, sound waves, water waves, etc.), the famous Doppler effect is formed. The Doppler effect refers to the phenomenon that the waves emitted by an object change continuously with the movement of the object or the observer. In front of the moving wave source, the wave is compressed, making the wavelength shorter and the frequency higher; conversely, the wavelength behind the wave source becomes longer and the frequency becomes lower. Just like a car coming from a distance, the loudness of the sound you hear is increasing, which is the result of the compression and superposition of sound waves.

Doppler effect

Source: Tencent

When an aircraft reaches supersonic speed, the aircraft as a sound-making body has exceeded the speed of sound propagation, the surrounding air is highly squeezed, and when breaking through the sound barrier, a large amount of energy is concentrated and burst out, forming a strong explosion sound, which forms a sonic boom.

Causes of sonic booms

Source | "What Is a Sonic Boom_ And How It Breaks Every Rule You Know"

So people found that as long as the speed of an object is fast enough to reach supersonic speed, the object can break through this barrier. At the same time, a strong shock wave will be generated around the object. We can hear the "pop" explosion sound and sometimes see a cone-shaped cloud visually.

The first sonic boom was discovered in 1947 when an American pilot flew an X-1 aircraft at a speed of 1,278 kilometers per hour in the air. With a loud bang and a cloud of mist, humans broke the sound barrier for the first time, and the pilot was also the first person in human history to surpass sound.

American pilot who broke the speed of sound

Source | "Chuck Yeager Breaks the Sound Barrier -- X-1 -- 1947"

2. The whip is swung at supersonic speed

A small whip, after going through a set of professional movements, will gather a lot of energy at the tip of the whip, and its speed can often reach twice the speed of sound. This phenomenon is the "sonic boom".

Whip

Source: Screenshot from the video "Smarter Every Day"

But the loud noise is not just the result of the whip tip. Recently, scientists have found through mathematical model analysis that a whip forms a ring structure in the direction of movement during the swinging process, and this structure can also produce sonic booms when moving at the speed of sound. When the whip ring structure moves at the speed of sound, the speed of the whip tip can reach several times the speed of sound, increasing the loudness of the sound.

Perhaps the whip-cracking uncles in the square don't know that they are so close to supersonic speed, and the whips in their hands can also break the sound barrier. It is true that there are masters among the people! However, it is precisely because of this that the sport of whip-cracking is somewhat dangerous. When exercising, you must pay attention to the people and environment around you.