I took the photos below during my visit to Theodore Roosevelt National Park (The Badlands) in North Dakota. The spherical boulders featured in the photos are a type geological formation called “cannonball concretions”. Concretions can range from fractions of an inch to more than 9 feet wide. They are formed when minerals are deposited around a core. Many concretions found in sedimentary rocks like sandstone or mudstone have a fossil at its center. These concretions form when carbon salts such as carbonate or bicarbonate leach out from decaying organic matter and react with calcium in the surrounding environment to produce calcium carbonate (calcite) which precipitates around the dead organism also acting like glue that traps in grains of sediment. Eventually, the layers of sediment around the concretion are compacted and cemented into rocks. The material of the concretion is harder and therefore more resistant to erosion than the surrounding rock. You can see some of the concretions in the photos below are still surrounded by the softer sedimentary rock that is slowly being eroded away.
I have mentioned non-Newtonian fluids before. One interesting property of these fluids is that when pressure is applied to them they turn into solids. In the video below, Kevin (aka TheBackyardScientist), teams up with Mark Rober to ask what happens when an extreme pressure is applied to a non-Newtonian fluid like Oobleck (cornstarch and water), which is of course a great excuse to use chainsaws, BB guns, and a golf ball propane cannon!
Hydrogen is the simplest element and occupies the first slot of the periodic table. Hydrogen is extremely reactive, and because of this, most of the hydrogen on Earth is found combined with other elements. Hydrogen gas is made up of two atoms of hydrogen. When hydrogen reacts with oxygen it releases a lot of heat, so not only has hydrogen gas been used in many applications ranging from rocket fuel to blowtorches, but the fact that the end product of the reaction is water makes it a clean source of energy. Hydrogen gas also has a density lower than that of air, so it floats and was used to create buoyancy for many of the so-called airships (aka dirigibles or zeppelins).
During their heyday from the early 1900s to 1937, airships were a sight to behold in the skies, and they became very popular making their way into things ranging from children’s toys and postage stamps to songs. Since hydrogen is flammable, helium was considered a much safer gas to fill the air ships. However, helium was expensive to obtain and not as buoyant as hydrogen. An airship could carry a significantly bigger payload when inflated with hydrogen. The most famous and largest of the airships was the German airship, Hindenburg, which Nazi Germany often showcased for propaganda purposes. The Hindenburg flew the world and crossed the Atlantic more than a dozen times until its fiery demise in an airfield in Lakehurst, New Jersey in 1937. The leading hypothesis for the explosion is that static electricity buildup in the Hindenburg’s metal frame, as a result of storms in the area, set fire to the hydrogen gas. The Hindenburg’s notorious accident was the last of a long list of hydrogen airships mishaps, and it put an end to the airship era. The explosion was captured in film and has become one of the most recognized disasters in human history (see video below).
The famous narration of the event in the video above is by journalist Herbert Morrison. Back in 1937 the narration and the film were not presented simultaneously. The narration was recorded, processed, and later played over the radio, and the film was shown in theaters. Only decades later were the two put together. Morrison’s narration is also famous because he employs the phrase “Oh the humanity” which has become a cultural trope used in many contexts in the modern era.
In the video below, Jared Owen uses 3-D animations to explain what happened to the Hindenburg.
Tetanus is a unique disease. It is not transmitted from person to person, and is only acquired when the infectious agent enters the body through a wound. The organism responsible for the disease, the bacteria Clostridium tetani, cannot be eradicated because it is found in the soil, intestine, and feces of humans and farm and household animals in the form of spores which are resistant to chemicals and heat and can survive decades. The pathology of the disease is caused by a potent neurotoxin released by the bacteria, so low levels of infection can be enough to cause death, and recovering from the disease does not produce immunity (there is no natural immunity). Only vaccination confers immunity to the disease. Today in the US there are about 30 cases of tetanus per year, mostly in unvaccinated individuals or those who did not receive booster shots. The video below from the folks at the Gene Technology Access Center contains excellent animations that explain the process of infection and how the pathology of this vaccine-preventable disease is produced.
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.