Physics trivia

# Five Physics Myths You’ve Always Believed

Physics is a science full of curiosities and myths. Know some myths of Physics that you possibly already believed.

Physics is a science that explains from subatomic phenomena to the formation of galaxies, so it is full of curiosities, but also of several misconceptions. We have gathered some myths of Physics that you may have believed in so you can learn a little more about this important area of ​​knowledge.

## → A coin dropped from the top of a building could kill someone

Many people believe that a light object such as a coin, if dropped from the top of a building, would hit the ground with potentially lethal speed. Perhaps this would be true if we could disregard the air resistance acting on this coin. However, the coin is strongly influenced by friction with atmospheric air, and during its fall, it quickly stops accelerating, reaching a terminal velocity .

Detached from the tallest building in the world, the Burj Khalifa, with its 828 meters, a coin like the 50 cent coin would reach a maximum speed of approximately 95 km/h , a speed insufficient to pierce the human skull.

Even dropped from the tallest building in the world, a coin wouldn’t be able to kill someone.

## → The Sun is yellow

The Sun is usually represented in drawings with the color yellow, however, it emits all the visible colors of the electromagnetic spectrum and therefore its color is white. The Sun is classified as a main-sequence star, that is, its energy comes from the fusion of hydrogen atoms into helium atoms — losing, in the process, about four million tons of mass per second! Its spectral classification, in turn, places it in the yellow dwarf category. Such classification does not concern its color, but the temperature of its surface, which is approximately 5500 ° C The yellow color of the Sun arises due to the scattering of light in the Earth’s atmosphere: atmospheric gases are able to absorb the highest frequencies of visible light , such as blue and violet.

## → In space, there is no weight

It is considered that from 100 km from the Earth’s surface space begins. Many people believe that after this distance, your weight would cancel out, as if there were no gravity , which is not real. An example of this is the international space station (ISS), which is approximately 400 km high, where gravity is approximately 8.3 m/s² . For astronauts to experience the sensation of weightlessness , that is, the sensation of being weightless , it is necessary for the ISS to orbit the Earth at approximately 28,000 km/h . This high rotational speed produces acentripetal acceleration capable of balancing the local acceleration due to gravity.

Dark energy and dark matter are two concepts you’ve probably heard, but they’re different things. Dark energy is a theoretical proposal to explain the increase in the expansion speed of the universe. It is the most accepted hypothesis to explain the inflation of the universe. According to this theory, created in 1980 by physicists Alan Guth and Alexei Starobinky , dark energy permeates the entire universe, acting as negative pressure would act on an inflated balloon: when the pressure in the surroundings of a balloon is removed, it swells up, due to its internal pressure.

The most recent calculations in Cosmology indicate that 67% of all energy in the universe comes from dark energy.

Dark matter , in turn, is believed to make up 85% of all matter in the universe. This hypothesis is due to the impossibility of the formation of galaxies as we know them, since, for that, a much greater gravity would be necessary. Some cosmologists believe that such an unknown mass comes from as yet undiscovered subatomic particles.

Only the mass of galaxies does not explain their formation.

## → Newton and the case of the apple

The story goes that Isaac Newton formulated the theory of universal gravitation after observing the movement of a falling apple, around the year 1660. There are still some variations of this account in which the apple falls on Newton’s head. However, none of them are real.

In fact, the story was invented by Newton himself, since at the time he claimed to attribute his discovery to the story of the apple, he was still a long way from developing all the mathematics necessary for determining the law of gravitation.

One of the myths of physics concerns the apple that fell on Newton’s head.

At the time Newton made the apple claim, he was in a great and long-running dispute with the English physicist Robert Hooke over the “paternity” of the law of gravitational attraction, which showed that the gravitational force depended on the inverse square of the distance between the bodies.

Today, it is known that the theory of gravitation was created by Isaac Newton from his third law, the law of action and reaction. However, this law was only formulated in the latest draft of Newton’s main work, the book Principia, 20 years after its original publication in 1685. Furthermore, Newton was able to arrive at the final form of this law through the application of the method developed by Hooke.