Experiments that researchers have performed throughout history in various scientific fields are like fuel for a device. If one has a theory about how the world is, one must first weigh the simple laws of physics with that theory to determine its validity. If your experiment conforms to these physical laws, your theory is acceptable. Otherwise, it must be reformed again to comply with the basic laws of the world.
Almost all recent scientific discoveries have been based on theories, and these theories have increased since we realized the function of the big world in understanding the small world. However, all these theories were based on experimental experiments, and it can be said that the history of science is in fact the history of experiments.
The great goals that we have achieved to date and with which we have increased our understanding of the world around us have been accomplished through very simple but ingenious experiments. If tomorrow morning a space creature hits your house and asks you how the universe works, you can explain to him these ten physical experiments that have changed our understanding of it.
1. Everything falls at the same speed
In 1589, the Italian scientist Galileo Galilei spent most of his time understanding the basic concepts of the universe, such as light, motion, and gravity. By the time Galileo lived, science had not changed much since the time of the ancient Greeks. In ancient times, Aristotle, one of the most influential Greek scientists, had argued that heavier objects fell faster than lighter objects; As a rock falls to the ground faster than a feather.
Hundreds of years after Aristotle, Galileo proved with his famous experiment that this statement was wrong. He dropped two balls of different masses from the top of the Leaning Tower of Pisa, and it turned out that despite their different weights, the two balls landed at the same time. According to Galileo, a feather hits the ground later than a rock due to its high friction with the air.
It may be interesting to know that one of the scientific experiments that NASA astronauts on the Apollo 15 mission to the moon had to perform was to simultaneously drop a rock and a full one at a fixed height on the moon’s airless surface. At the end of the experiment, it was once again proved that all objects fall at a constant gravitational field, such as the earth or the moon, at a constant speed.
2. White light is emitted in a color spectrum
I think it goes without saying that the rainbow is formed after rain by the refraction of light in raindrops, and its color spectrum is revealed by the scattering of components of sunlight in the sky. But until 1672 AD, when Isaac Newton performed his experiment, no one knew how the rainbow formed.
Newton performed this simple experiment with a glass prism and sunlight from his room window and found that white light consisted of a color spectrum with different wavelengths of visible light, from blue to red. He even showed that the wavelength of blue is shorter than the wavelength of red, and after red there is another wavelength called infrared that is invisible to our eyes and we only feel it as heat.
This red wavelength is now used to observe distant stars, and missions such as the James Webb Space Telescope are specifically designed to receive this wavelength.
3. Earth mass measurement
Henry Cavendish was able to measure the mass of the earth in his famous experiment in 1798. He connected two spheres of equal mass to the two ends of a rod and two more spheres of equal mass and more than the previous spheres to the other two ends of the rod. Cavendish connected the center of mass of the two rods at one point and placed a mirror in the center of the rod of the smaller spheres.
He moved the two large spheres carefully and slowly, observing that the two smaller spheres moved under the gravitational field of the larger spheres. Cavendish was able to measure the change in angle of the small rod and finally calculate the mass of the earth by shining a point light source on a mirror placed in the center of the small rod.
Of course, in addition to measuring the mass of the earth, Cavendish was able to calculate the universal constant of gravity, G, and later became the basis of Newton’s universal law of gravity.
4. Experiment with two slits and the particle-wave property of light
Isaac Newton thought that a beam of light travels in the sky like a train of very small particles called a “corpuscle” – which means particle. But in 1803, Thomas Young performed a simple experiment Designed And changed our perception of light forever.
In a dark screen, he made two narrow apertures nearby and placed a light source about a meter away. Yang placed a light-sensitive film (like old negatives) behind a dark screen and turned on the light source for a short time.
Young predicted that if Newton was right, the center of the sensitive film would have more light and the corners of the film would be darker. But the result of this experiment left a dark and light pattern on the film, which showed that light was emitted in waves in space.
In 1905, Albert Einstein showed that light could also act as a particle. By shining light on a metal plate under certain conditions, he was able to transfer electrons from it to another metal plate. Einstein received the 1921 Nobel Prize for his design of this experiment, called the photoelectric effect.
After the introduction of these theories, scientists came to the conclusion that light behaves as both a wave and a particle. The dual wave-particle behavior of photons is one of the most important and fundamental physical principles in quantum theory.
5. Energy conservation: Energy is not lost, but is transformed from one state to another
Think you want to run a marathon. A simple rule called conservation of energy states that you must store energy in your body for a distance of 42 kilometers. In other words, to do anything, you must have the energy needed to do it.
James Joule conducted an experiment in 1840 solar 1219 and placed a water turbine in a chamber filled with water. The turbine was attached to a shaft that extended out of the chamber. The rope was wrapped several times around the rope and continued to be attached to a spool with a weight at the end.
When Jules released the weight, the weight of the rope pulled around the spool, moved the rope of the rod, and spun the turbine inside the chamber, and finally, the water inside the chamber warmed up. He dropped the weight 20 times to warm the water enough to measure the temperature difference.
Joule found in his calculations that the potential energy stored in the weight was exactly equal to the heat energy transferred to the water. In other words, Jules acquired the same repetitive textbook phrase; Energy is not made or destroyed, but transferred from one state to another.
6. Measuring the speed of light
Light travels so fast that a beam of light can travel around the earth seven times a second. The question that arises is that if the speed of light is so high, how could we measure its speed at all?
About 170 years ago, the French scientist Hippolyte Fizo Rahi Found With which it can achieve the speed of light. He shone a beam of light on a mirror at a certain angle to pass through a spinner at hundreds of revolutions per second. Fizo placed another mirror in front of the gear, 8.5 km away, to reflect light in the same direction. Fizo saw the light again through a telescope as it passed through the gear.
He knew how far a beam of light traveled in this direction, and it was enough to measure the time it took to see one beam to another. With this method, Fizo achieved a speed of light of 310,000 kilometers per second, which was about 5% faster than we know today.
Leon Foucault later modified the experiment by replacing the gear with a rotating mirror. With this method, he achieved a speed of light of 298 thousand kilometers per second, which is almost one percent less than the known speed of light today.
7. Robert Millikan experiment to measure electron charge
We know that electrons carry an electric charge, so the least amount of electric charge that can be had is the amount on an electron. But how can the electric charge on such a small particle be measured?
In 1909, Robert Millikan was able to design an experiment that could measure the amount of unit electric charge on a single electron. He placed two plates with different electric charges in front of each other and sprayed oil droplets between the two plates. Millikan injected some electric charge into the droplets and found that they deflected at different angles to different planes, depending on the amount and type of charge they received.
By measuring their deflection angle and velocity, Millikal was able to find a ratio between the electric charge of these droplets. He also estimated the charge per drop of oil and was able to calculate the charge of an electron with good accuracy. Millikan received the 1923 Nobel Prize for this experiment.
8. Ernst Rutherford gold foil test and generalization of the atomic model
“Atom” is a Greek word that ancient thinkers attributed to the smallest particle of which everything is made, and most importantly, “can not” be broken down into smaller pieces. This thought was with us until the end of the nineteenth century, until between 1897 AD / 1276 AD. Until 1932/1311 Several experiments were performed to show that the atom, an indecomposable particle, was made up of smaller particles.
The experiments began with Thomson discovering electrons, and Ernst Rutherford and his students performed a famous experiment with a thin sheet of gold that found that the nucleus of an atom was made up of positively charged particles. Finally, James Chadwick discovered neutrons in the nucleus of an atom. It’s to say that we owe the three atomic models we know today.
Ernest Rutherford and his students at the University of Manchester bombarded a thin sheet of gold with alpha particles (positively charged particles). Rutherford predicted that if there were positively charged particles in the nucleus of an atom, these alpha particles would hit the nucleus and bounce back.
Although most particles passed through the gold foil and a small amount deflected at low angles, the team found that after a series of attempts, a number of high-angle particles deflected and a handful of them returned directly.
“It’s like throwing a 40-centimeter ball at a piece of tissue paper and the ball goes back to you,” Rutherford famously said after the experiment. He was able to measure the size of a gold atom and its nucleus, showing that the nuclei of all atoms are made up of positively charged particles called protons, around which electrons revolve. He also noticed that 99% of the atoms made up of empty space, as most of the particles passed through the gold leaf.
9. Nuclear chain reaction test
By 1942, when the Italian scientist Enrico Fermi performed his experiments, the structure of the atom had been fully determined, and according to Albert Einstein’s theories, everyone knew that mass and energy were equivalent and could be converted in some way. کرد. In other words, if you can separate a very small mass like the nucleus of an atom, a lot of energy will be released.
Fermi according to this experimental principle called “atomic candle” at the University of Chicago Designed. In his experiment, he threw a neutron (a chargeless particle inside the nucleus that holds protons together) into a uranium-235 atom to produce uranium-236.
You should probably know that natural elements have different atomic masses called isotopes. Now, in order to be able to distinguish different isotopes of an element, scientists bring the atomic mass of each isotope after the name of the element. In this case, we know that the isotope uranium-236 has one more mass unit than uranium-235.
But uranium-236 is an unstable isotope that quickly turns into two smaller atoms, releasing several neutrons. These released neutrons collide with nearby uranium-235 and again produce unstable uranium-236, and this reaction continues in a chain until the end of the uranium.
This chain reaction took place at the world’s first nuclear power plant in Fermi Laboratory and is now occurring in all nuclear power plants around the world.
10. X-ray photography of DNA
Francis Crick and James Watson, along with Maurice Wilkins, received the 1962 Nobel Prize in Medicine for their efforts in understanding the structure of DNA and X-ray photography in a special way. X-ray diffraction is a method by which the internal structure can be studied by shining an X-ray on an object such as the human body and creating a shadow behind it.
Of course, this Nobel Prize was not awarded to an important person named Rosalind Franklin, who died of cancer four years before this Nobel Prize. Although Franklin’s efforts He was instrumental in understanding an important part of the structure of DNA, he was never known as much as Crick, Watson and Wilkins.