# Speed ​​- Natural Sciences – Physics

We explain what speed is and some characteristics of this scalar magnitude. Also, a practical example of speed.

What is speed?

Speed ​​is the variation of distance in a specific time as a consequence of the movement of a mobile element. In this case, the term “mobile,” can cover anything from a machine (such as a car) to a particle, such as an electron or any other body capable of moving in space.

Speed ​​is a scalar quantity and not a vector quantity, unlike velocity. This means it has a value and a unit but not an address. The speed is, finally, the absolute value of the speed.

For example, if we say that a bus moves along an avenue with a speed of 82 km/h, we know that the value of the rate is 82 and its unit is km/h (kilometers per hour), but we do not know in what address it does. In other words, after a specific time has elapsed, we will learn how far it traveled, or vice versa, how long it took to travel a certain distance, but we will not know where it is located in space.

Although the term is expressed as distance/time, this does not mean that the mobile has moved at the same speed during the time interval studied. That magnitude could have varied infinitely, but the average of the volumes is one of interest.

Speed ​​of light

We explain what the speed of light is and what it is for. Also, the story of its discovery. It’s essential in different fields.

What is the speed of light?

The speed of light is a measurement stipulated by the scientific community, generally used in the fields of science of physical and astronomical studies. The rate of light indicates the amount of distance that light travels per unit of time.

It is essential to study celestial astronomical bodies to know their behavior, the transmission of electromagnetic radiation, and how the human eye perceives light.

If we know the distance, we can learn how long it takes light to travel. For example, sunlight takes approximately 8 minutes and 19 seconds to reach Earth. The speed of light is considered a universal constant, invariant in time and physical space. Its value is 299,792,458 meters per second or 1080 million kilometers per hour.

This speed is related to a unit of length widely used in astronomy, the light year, which refers to the distance traveled by light in one year.

The speed of light we have presented is what it has in a vacuum. However, light is transmitted through other media, such as water, glass, or air. Its transmission depends on specific characteristics of the media, such as electrical permittivity, magnetic permeability, and other electromagnetic characteristics. There are physical areas that electromagnetically facilitate its transmissibility and others that hinder it.

Understanding the behavior of light is crucial for astronomical studies and understanding the physics with which satellites are orbiting the Earth.

History of the speed of light

The Greeks were the first to write about the origin of light, and their thought was that light emanated from objects, and then the human vision was emitted to capture it.

Until the 17th century, light was not considered to travel but was conceived as an instantaneous phenomenon. However, this changed from the observation of eclipses. It was recently Galileo Galilei who, by carrying out specific experiments, questioned this principle of “instantaneity” of the distance that light travels.

Different scientists carried out several experiments, some lucky and others not; however, all these biological studies in this incipient scientific era pursued the objective of measuring the speed of light, even with the complications that their instruments and methods were inaccurate. And primary. Galileo Galilei was the first to experiment to measure this phenomenon, but he did not obtain results that would help calculate light transmission time.

Ole Roemer was the first to attempt to measure the speed of light in the year 1676 with relevant success. Using the study of the planets of the terrestrial shadow reflected on the body of Jupiter, Roemer detected that the time between the eclipses was shorter when the distance to the Earth decreased, and vice versa. He obtained a value of 214,000 kilometers per second, a fair number that gave the level of precision with which the distance of the planets could be measured at that time.

Then, in 1728, James Bradley also studied the speed of light but observed the transformation of the stars, detecting the displacement that occurred about the movement of the Earth around the Sun, from which he obtained a value of 301,000 kilometers per second.

A wide variety of methods have been used to improve measurement accuracy; for example, in 1958, the scientist Froome reached the value of 299,792.5 kilometers per second using a microwave interferometer, the most successful. From 1970, the measurement improved qualitatively with the development of laser devices with greater capacity, excellent stability, and cesium clocks that will enhance the accuracy of the measurements.

Speed ​​of light in different media (half-speed)

• Empty – 300,000 km/s
• Air – 2999,920 km/s
• Water – 225,564 km/s
• Ethanol – 220,588 km/s
• Quartz – 205,479 km/s
• Crown glass – 197,368 km/s
• Flint glass – 186,335 km/s
• Diamond – 123,967 km/s