Something About Sforno — A Short Dvar Torah on the Parsha — Va’era 5769
Aerodynamics of Egyptian Hail
US Air Force test pilot, Chuck Yeager, is credited as being the first person to break the sound barrier on October 14, 1947, in the Bell X-1. Many pilots before him died trying. It took test pilots and engineers many years to understand and overcome the many issues surrounding traveling faster than the speed of sound. Some scientists thought it was impossible and aircraft would break apart from the extreme pressure and vibrations as they approached the sound barrier.
In the early days of the cold war, the one critical element lacking in the development of nuclear missiles was known as “atmospheric reentry technology”. Scientists discovered that anything they sent into space or even the upper atmosphere would burn up on reentry. As such they needed to develop proper shielding technology to protect the “payload”.
Sonic booms and atmospheric reentry burnout were technological issues that were not even dreamed off until a few decades ago.
As such, it is outright incredible that Rabbi Ovadia Sforno describes both of these phenomena in his commentary about half a millennium ago.
In Exodus 9:23-24 the Bible recounts:
“And Moses outstretched his staff to the heavens, and God gave sounds and hail, and fire descended earthward, and God rained down hail upon the land of Egypt. And there was hail and fire together in the hail, very heavy, the like of which was not in Egypt since it’s becoming a nation.”
Sforno comments on the “fire descended”:
“The flaming air descended to the earth with the force of the movement of the hail that pressed on it (the air) during its descent.”
Sforno basically and accurately described atmospheric reentry during the same period of time when Leonardo Da Vinci was playing with his water engine.
“In the force of the movement of the hail during its descent, the air was flamed and produced sound.”
He’s talking about sonic booms!
Imagine an ongoing downpour of burning hailstones accompanied by continuous sonic booms. It’s no wonder Pharaoh is frightened out of his wits and begs for the noise to stop before mentioning the hail.
The fact that Sforno was able to describe scientific concepts that we think of as exclusively from our modern era simply leaves me awestruck.
May plagues continue to hail down on our enemies, and may we be spared, and like our ancestors may we witness redemption.
To the memory of Dr. Irwin Rochwarger, a beloved mentor and teacher. As an engineer who designed and built satellites for NASA, amongst many other amazing technological feats, he would have appreciated very much Sforno’s insight.
The term sonic boom is commonly used to refer to the shocks caused by the supersonic flight of an aircraft. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion. Thunder is a type of natural sonic boom, created by the rapid heating and expansion of air in a lightning discharge.
When an object passes through the air, it creates a series of pressure waves in front of it and behind it, similar to the bow and stern waves created by a boat. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot “get out of the way” of each other, eventually merging into a single shock wave at the speed of sound. This critical speed is known as Mach 1 and is approximately 1,225 kilometers per hour (761 mph) at sea level.
The cracking sound a bullwhip makes when properly wielded is, in fact, a small sonic boom. The end of the whip, known as the “cracker”, moves faster than the speed of sound, thus resulting in the sonic boom. The whip was the first human invention to break the sound barrier.
A bullwhip tapers down from the handle section to the cracker. The cracker has much less mass than the handle section. When the whip is sharply swung, the energy is transferred down the length of the tapering whip. In accordance with the formula for kinetic energy, the velocity of the whip increases with the decrease in mass, which is how the whip reaches the speed of sound and causes a sonic boom.