The law of conservation of energy states that energy cannot be lost or gained but just converted from one form to another. For example, when a pendulum is elevated to a certain height it acquires a potential energy. When the pendulum is released that potential energy is converted to kinetic energy in the downswing and back into potential energy in the upswing. However, unless a source of energy is introduced into the system such as, for example, giving the pendulum a push, the pendulum will not reach a higher elevation than the one from which it was originally released. In the video below, uploaded into You Tube by Johnny Rico, Professor Walter Lewin from the Massachusetts Institute of Technology (MIT) puts his life on the line to illustrate this principle.
During a large explosion the air is pushed away from the center of the explosion and compressed into a supersonic shock wave, which creates the loud sound we hear from the blast. Immediately behind the shock wave an area forms of low pressure and temperature. If the explosion is sufficiently strong and occurs in a humid environment, the temperature of the air behind the shock wave can briefly drop below the dew point causing water molecules to rapidly condense into water droplets forming a cloud. In the first atomic bomb tests carried out in the Bikini Atoll in 1946 (Operation Crossroads), these clouds were called Wilson Clouds. They were named after the Scottish physicist Charles Thomson Rees Wilson who won a Nobel Prize (shared with the American physicist Arthur Compton) in 1927 for the development of the cloud chamber which allowed the visualization of radioactivity.
In the video below, an atomic bomb named “Baker” is exploded underwater next to unmanned ships to test its power. You can see the large Wilson cloud begin to develop around the huge central column of water 9 seconds into the video.
Today Wilson clouds are called “condensation clouds”. Condensation clouds can also form during far weaker explosions under the right conditions such as the one that rocked the port of Beirut in 2020. The white condensation cloud begins to develop 11 seconds into the video. It envelops the central red-colored explosion cloud and then quickly dissipates.
However, man-made condensation clouds are not only formed during explosions. Anything capable of generating a supersonic shock wave such as a fighter jet can generate such a cloud, which is this case is called a vapor cone.
Many engineering schools hold annual egg dropping contests. These are competitions where students have to design a contraption that will protect an egg from breaking when dropped from a certain height. Far from this being merely a fun pursuit, the different designs that are employed by the students allow them to get acquainted with the physics and strategies that have been employed to solve real problems ranging from saving human lives lives during car collisions to landing multimillion dollar probes safely on distant planets. In the video below, Mark Rober explains the physics behind protecting an egg during a drop from a bridge and walks us through several designs that have been successfully employed.
Below is a photo I took (you can see my reflection on the fuselage) of the, Enola Gay, now on exhibit at Air and Space Museum’s Steven F. Udvar-Hazy Center in Virginia. The Enola Gay was the airplane that dropped the first atomic bomb on August, 6 1945 on the Japanese city of Hiroshima killing 70,000 people in less than a second and tens of thousands more from radiation by the end of that year. The bombing of Hiroshima and that of another Japanese City, Nagasaki, 3 days later ended the Second World War and ushered the nuclear age setting in motion political, social, and cultural changes what would reshape the world forever affecting the lives of hundreds of millions of people.
In a segment of a CNN documentary below the last surviving member of the Enola Gay crew, Theodore Van Kirk (1921-2014), reminisced about the war and the bombing.
The nuclear age also had dramatic effects on science in terms of new scientific discoveries and applications as well as the way science was conducted. The names of many of the physicist who worked on the Manhattan project, which produced the first atomic bomb for the United States, have become the stuff of legend being celebrated or vilified in movies, word, and song. Among them stands out the scientific director of the Manhattan project, Robert Oppenheimer, who upon the explosion of the first atomic bomb famously remembered a line from the Hindu text, the Bhagavad Gita, “Now I am become Death, the destroyer of worlds”.
The photo of the Enola Gay belongs to the author and can only be used with permission.
Besides clapping your hands and snapping your fingers, there is another way to make sounds with your hands. The approach I show in the video below exploits the facts that the palms of your hands are concave, and that when you place your hands opposite to each other and introduce a slight twist, the area around your palms acts like a seal turning both of your hands into suctions cups. Once you have arranged your hands in this position, you can press them against each other forcing out the air between them which will make a sound. The expelling of the air will create a low pressure area (not a vacuum, see below) between your hands, and when you break the seal, the air will rush back in and produce another sound. By pressing and releasing your hands repeatedly against each other you can rapidly produce rhythmical sounds.
It is important to understand that the reason air rushes in when you break the seal is not that the air is “sucked in” by the vacuum in between your hands. As I have explained in my blog, vacuums don’t suck; it is the atmosphere that pushes. A column of air hundreds of miles high above you excerpts a pressure of 14.7 pounds per square inch (at sea level) on your hands. When you move your hands or fingers and break the seal, it is all that pressure that pushes the air back in.
While clapping hands and snapping fingers are well known descriptions of how to make sounds with your hands, I don’t know what word to use to describe the method that I used in the video to produce sounds with my hands. If you know or want to suggest (or invent) a verb for it, please leave a comment below!
In the video below, Derek Muller, of the YouTube channel Veritasium, explains a bizarre behavior of some rotating bodies called the Dzhanibekov Effect. From spinning tennis rackets on Earth to spinning wing nuts in space, and from Soviet era secrets to speculations about the end of the world, Derek’s video is an amazing combination of storytelling, history, and explanation of science principles. Enjoy!
Kevin and the rest of the folks from the TheBackyardScientist decided to ask what happens when you put 20,000 Joules of Energy into a watermelon and other things. Why? Why not? Is it science? Is it art? Who cares (except the neighbors who threatened to call the cops on them)? It’s cool, Dude! Watch their video and also learn about capacitors.
Newton’s Cradle is a device that is used in teaching to demonstrate the physical laws of conservation of energy and momentum. The device consists on a series of spheres suspended from wires. The spheres are pulled and released, and then collide with each other. But there must be something charming about Newton’s Cradle which has made it transcend the classroom, as it is used is also used for entertainment, or as a decorative toy, and has even been featured in movies. When the moving ball collides with the stationary balls, the force is transmitted through the stationary balls to the ball on the far side. Depending on the number of moving balls and stationary balls as well as their location and the timing of release of the balls, several recurring collision patterns can be generated as shown in the video below.
If you have the time, there is even a computer simulation of Newton’s Cradle that you can operate without having to deal with the effects of friction which eventually dampen the performance of the real device.
An ability of cats that has intrigued people throughout the ages is their capacity to land on their feet when falling, even if their legs initially point away from the ground. Cats are able to right themselves in midair, and scientists have studied the reason why and have come up with mathematical models to explain it. Research into the physics of falling cats funded by the National Aeronautic Space Administration (NASA) has generated information useful for astronauts trying to turn themselves around in conditions of zero gravity.
Destin from SmarterEveryDay performs a cat dropping demonstration in the video below and addresses the physics involved in the process.
The domino tumble is a great example of the conversion of potential energy into kinetic energy (energy of movement) and the internet is filled with videos of elaborate domino tumbles involving thousands of dominoes such as the one below.
Less well known variants of the domino tumble are the double domino and domino amplification effects.
The double domino effect occurs when the regular forward wave of toppling dominoes is followed by a second wave in the opposite direction. This occurs because the first wave leaves the dominoes lying partly on top of each other with some of their potential energy still intact. When the terminal domino falls to the ground, it fails to provide the support needed for the domino immediately before it which falls to the ground too followed by the next one and so on. The process and the math involved are explained in the video below by Matt Parker from standupmaths.
The domino amplification effect is a far more interesting for me because with a tiny input energy you can release a huge amount of energy in a process that is somewhat similar to a chain reaction. This is possible because a domino can topple over another domino that is 1.5 times larger. Thus by placing dominoes of increasing size one after the other you can topple a gigantic domino using a much smaller one achieving amplifications factors in the billions. The process and the physics involved are explained in the video below.
The domino amplification effect was featured in an episode of Mythbusters shown in the video below.