# Those racking weighing methods

What is your weight? When you want to know the answer, just stand on the scale and you will know it immediately, although it may become a secret that only you and the scale know. We can easily weigh objects of moderate size like humans. How to weigh those “overweight” or “too thin” objects?
UAVs weighing
who say the world’s biggest and heaviest of animals, it is none other than the non-blue whale, then how do we give such huge animals weighing it? Perhaps the first thing that comes to your mind is the story of “Cao Chong called the elephant”. It just so happens that the whale itself lives in the water and drains too easily. But the weight of whales is several to several tens of times larger than elephants, and it is not easy to weigh the discharged water. Is there a better way?
Ask the farmers who raise pigs for this question. They have their own magic formula. Prepare a tape measure. First measure the body length of a pig, that is, the length from the head to the buttocks, and then measure the pig’s “chest circumference” approximately at the center of the body, and then calculate the size of the pig. The density of the pig is basically the same. Multiply the known pig density by the pig’s volume to get its weight. The weight error of pigs calculated by this method is only a few hundred grams, which is convenient and fast.
The method of weighing whales is similar, except that the tool for measuring the whale’s body length has been changed from a tape measure to a drone. Using this method, researchers recently measured the weight of a group of right whales in Argentina. When right whales swim to the surface of the sea for breathing, they will be taken by drones flying in the air to take a group of “naked photos”. From these photos, the researchers calculate the length and width of the whales, and then use cylindrical The calculation formula calculates their volume. The density of whales is also estimated. They found the weight and “measurements” of the previously killed whales to calculate their density. Finally, multiply the density by the volume to get the estimated weight of the right whale.
Botanists use a similar method to measure the weight of towering ancient trees. The height of the trunk is measured by drones, and the tree circumference is measured to calculate the trunk volume, and multiply it by the density of the same tree species to get the trunk weight. The weight of the canopy needs to be calculated by sampling method. Calculate the weight of the leaves on a small branch, multiply it by the number of branches, and finally add the weight of the trunk to estimate the weight of the tree.
Know the weight of the virus
Measured the weight of the heaviest creature on the earth, how should the weight of the lightest creature, the virus, be measured?
Do you have this experience? If a mosquito falls on its arm, it can hardly feel its presence when it is still, but if it vibrates its wings or “walks” on its arm, it can feel its weight. The measurement of the virus has also borrowed from a similar method. However, it is not the arm that measures the weight of the virus, but the laser beam. A team at the Massachusetts Institute of Technology has created such a virus (cell) weighing instrument. In order to reduce the interference of air fluids and particles, the weighing instrument needs to be placed in a vacuum environment, but the virus cannot live in a vacuum, so the researchers first drop a drop of water on one end of the silicon wafer balance, and then place the sample in the water drop. . A beam of blue laser is irradiated on the water droplet. When the sample is put into the water droplet, the frequency of the beam will change. By measuring the change in the light frequency, the quality of the sample can be calculated. Finally, the weight of a single virus is only 8.5× 10-19 grams.
How particles called
Although the virus so “slim”, in fact, there are more “thin” than it’s something that is composed of particles of matter – atoms, neutrons and electrons, scientists have come up with several ways to say them weight.
As early as 1912, the physicist Thomson invented the “weight scale” of particles-the mass spectrometer. It works like this: Researchers fill its “belly” with hydrogen, and then inject it into the hydrogen. Beam of protons. When protons meet some hydrogen atoms, they will take away the electrons of these hydrogen atoms, turning the hydrogen atoms into hydrogen protons (hydrogen ions). According to the physical formula, in the electric and magnetic fields, the strength of the electric field and magnetic force received by the particles is proportional to the charge of the ions. The electric field force accelerates or decelerates the ions, and the magnetic force makes them bend. Therefore, when hydrogen passes through a pipe under the action of electric and magnetic fields, the charged hydrogen ions will be “sucked away”, and those neutral hydrogen atoms that have not collided with the protons are unblocked in this pipe Unimpeded.
The “sucked away” ions will eventually hit the other end of the pipe. By measuring the location and time of the impact of different ions, physicists can determine what changes have occurred in the speed and direction of the ions due to the electric field and magnetism. . Finally, through the formula F=ma of Newton’s second law of motion, the mass of the ion is known by dividing the total force acting on the ion by the degree of velocity change.
Another method of weighing particles is similar to the virus weighing method. The carbon nanotube “balance” is placed in a low temperature and a vacuum, and the mass of the particles attached to it is calculated by measuring the change in the vibration frequency. The two methods finally The measured masses of hydrogen atoms are all about 1.6×10-24 grams.
Earth has multiple
compared with biologists, physicists can not only “called” a lighter weight, but also “called” a heavier weight, such as the weight of the earth.
We live on the earth. Obviously, there is nothing equivalent to the earth. Therefore, the drainage method cannot be used, and because the density of the earth is so different, the method of multiplying the density by volume cannot be used. Therefore, we must find another way to weigh the earth. Scientists did not think of a new method for a long time until Newton introduced the law of universal gravitation:, where F refers to the gravitational force between two objects, M and m are the masses of these two objects, r is the distance between the two objects, G Is the constant of gravitation. Then when M refers to the weight of the earth, we use a 1 kg iron ball as another object. Through free fall experiments, we can calculate that the gravitational force between it and the earth is about 9.8 kg*m/s, and the earth’s radius is 6.4 million meters. The distance r between the heart and the iron ball, the mass M of the earth can be calculated by measuring G again.
The physicist Cavendish measured the value of G for the first time. He fixed a small mirror to a quartz wire tied to a wooden pole, and used a telescope to manipulate and measure at a long distance outdoors to reduce the influence of air disturbance. Then fix a small shot ball with a diameter of about 5 cm on each end of the wooden pole, and place a large shot ball with a diameter of about 30 cm on each side of the small iron ball. The gravitational force existing between the two shot puts will cause the line that holds the shot put to swing slightly periodically. This swing will be transmitted to the small mirror through the quartz wire, and the light reflected by the small mirror can show the law of the swing, thus Cavendish The value of G is calculated.
In 2018, a team led by physicist Luo Jun, an academician of the Chinese Academy of Sciences, used a similar method to measure the most accurate G value, and the measurement accuracy reached 11 parts per million. They used two methods. The first is the same as Cavendish’s method, but because it is now possible to create a vacuum environment, the accuracy is improved. The second method is called electrostatic compensation. The thread attached to the shot ball also has a slight elastic force. The elastic force will reduce the gravitational force between objects and affect the measurement of G. The electrostatic force generated by the electric field is applied to the Luo Jun team to balance the elastic force of the thread, so that the measured G value is more accurate , The currently measured G value is 6.674484×10-11 m3/(kg·s2). Substituting all these values ​​into the universal gravitation formula, it can be calculated that the mass of the earth is 6×1024 kg.
With so many whimsical ideas, no matter the weight of any object, it is no longer a secret to us.