In West Asia, not far from the Mediterranean, there is an inland lake called the Dead Sea. There are no fish in the Dead Sea, hence the name. Why are there no fish? Because the water in the Dead Sea is too salty, there are more than 20 kilograms of salt per 100 kilograms of seawater. The density of dead seawater is too high, much higher than that of human body (the density of human body is about 1000kg/m3), so as long as more than half of human body is submerged under the water, buoyancy is equal to gravity. When people swim in the Dead Sea, they can lie on the water and read newspapers. It takes a lot of effort to sink into the water, and they will be lifted out of the water by the sea. The seawater of the Dead Sea is rich in minerals and can be used to treat some skin diseases and eczema. It is one of the famous swimming spots and health resorts in the world.
What do people walk on?
On the smooth road, anyone can stride forward. It is not difficult for a healthy person to walk, so he has never thought about what people walk on. Hearing this question, some people will find it funny. Can't people move forward as long as they have the strength to lift their legs and step? Actually, the problem is not that simple. Please try an action: stand up straight and stand on the ground with your back against the wall. Lift one foot and take a step forward. As long as you don't leave the wall, you can't cross this foot. If the raised foot takes a step forward, then, looking back, the body has left the wall. This shows that the body has moved forward. People must rely on an external force when they move forward. In other words, it is this kind of pushing people forward. If this external force is relatively small, it is difficult to walk. For example, on the smooth ice, people dare not take big steps, so they can only move their feet carefully. Now, please answer, your back pedal is on the ground. From a physical point of view, it is the human body that gives the ground a backward force, and the ground also gives the human body a forward force. It is this force that pushes the human body forward. Push the ground, this is force; The ground gives the human body a forward force, and this force is the reaction force. This reaction takes the form of friction. Generally speaking, the action and reaction are just equal, so we don't find it difficult to walk. However, when people walk on the ice, the ice is too smooth and gives people much less friction. In this way, if you still push as hard as walking on the ground, the force and friction of pushing backwards will be unbalanced. If your hind foot slips backwards, people will fall.
Why is it easier to pull a cart than to push it?
Trolley, easy to use, can be pushed and pulled. The direction of push-pull is the same as the angle of horizontal line. Is it easier to push or pull a cart? Labor saving is not labor saving, mainly depending on how much resistance the wheel receives. Because of overcoming the resistance, the car can move forward. Under the same ground conditions, the greater the wheel pressure on the ground, the greater the resistance, and the greater the resistance. On the contrary, the pressure is small, the resistance is small, and it is labor-saving. When pushing a cart, the direction of the force is inclined downward, which has two functions: one component moves forward to overcome the resistance and make the car move at a constant speed; The other component is vertical downward, which increases the pressure of the car on the ground and increases the resistance. When pulling the car, the direction of the force is inclined upwards, which also produces two components; A forward to overcome resistance; The other is vertical, which reduces the pressure of the car on the ground and reduces the resistance. Therefore, the resistance to be overcome when pulling the cart is small, which will save some effort.
Why do people with heavy loads walk like jogging?
When people walk, their left and right feet move forward alternately. If it is right, people's walking can be considered as a substitute for falling. When a person stands still, the vertical line drawn from the center of gravity of the human body is always in the area formed by two feet, which is called a state of balance when standing. When people start to move forward, they always lean forward first, so that the vertical line drawn by the center of gravity of the human body goes out of the bottom, forming a tendency to fall forward, and then immediately stride forward with their hind feet to maintain a new balance. So when we say step by step, we mean going forward again and again. This tendency is related to the weight of the human body and the size of the steps. The worse the tendency to fall forward, the heavier the landing is when the foot touches the ground, which not only makes people feel hard, but also makes it difficult to step steadily. Walking with load means that the weight of the human body suddenly increases a lot, and the tendency to fall forward is very strong. Shortening the stride can appropriately reduce this dumping trend; Taking your hind feet quickly can prevent you from really falling. Therefore, people who carry heavy loads always take small and urgent steps, which becomes a trot. Also, short steps when loading can make the speed uniform, so that the load can also move with people at a constant speed. If the pace is big and slow, the burden will be released, not picked.
Why is a bottle full of water not easy to break?
There are two identical glass bottles, one is empty, the other is full of water, and at the same time it falls to the ground from the same height. Which bottle breaks easily? Generally speaking, heavy bottles break easily. But when the bottle is filled with water, the water in the bottle has another function, which can reduce the deformation of the bottle and make it difficult to break. Most of the broken glass bottles are caused by deformation. When the empty bottle falls to the ground, the pressure is constantly exerted on the bottle, and the bottle is deformed from the outside to the inside and finally breaks. The bottle is full of water. Because water is incompressible, the deformation is reduced and the bottle is not easy to break. The bottle is filled with water, and then the cap is tightened, so it is more difficult to break.
Have we inhaled the soda?
We suck soda through a straw, always thinking that it is our mouth that sucks soda up. Actually, it's not. It only sucks the air in the straw. As for soda, it is the atmosphere that presses it into the mouth. It turns out that after the air in the straw is sucked away, the soda in the tube is reduced by the air pressure, while the soda in the bottle (outside the straw) is at atmospheric pressure. These two pressures are not equal. If the atmospheric pressure is higher, soda will be pressed into your mouth. If the soda bottle is covered with a cork and a glass tube is inserted in the cork, you can suck soda from the glass tube once or twice at most, and you will never get soda from the bottle again. The reason is also very simple, because the atmosphere outside the bottle can't enter the soda bottle, and the atmosphere can't press the soda into the mouth. Can I still drink soda without unplugging the cork? Although it can't be sucked up, can it be blown up? Blowing air into the glass tube is one way. Blowing increases the gas in the bottle and increases the gas pressure in the bottle. When the pressure of the gas in the bottle increases, the soda will be squeezed out of the glass tube. At this time, as long as the mouth does not leave the glass tube, soda can be drunk. The more you blow into the bottle, the more the pressure increases, and you can drink soda smoothly. After drinking some soda, the volume of gas in the bottle becomes larger and the pressure decreases, so you can't drink soda. Blow again, and you can continue to drink soda.
What is an energy storage power station?
Pumped storage power station is different from ordinary hydropower station. Generally speaking, only generators are installed in hydropower stations, and the water with high water level is used once and then discarded to the east. Pumped storage power station is equipped with both pumping and generating units. During the day and the first half of the night, the reservoir releases water, and the water with high water level passes through the dual-purpose unit. At this time, as a generator, the dual-purpose unit converts the mechanical energy of high-level water into electrical energy and transports it to the power grid. Solve the power shortage during peak hours; In the second half of the night, the power grid is at a low power consumption trough, and the power grid cannot store electric energy. At this time, the dual-purpose unit is used as a water pump (the dual-purpose unit can be reversed), and the redundant electric energy in the power grid is used to pump the water with low water level to the high water level, and then it is injected into the reservoir with high water level, so that the redundant electric energy in the power grid is converted into mechanical energy of water and stored in the reservoir when the power consumption is low. At the peak of electricity consumption, the reservoir releases water, and the mechanical energy of water is converted into electrical energy by the generator and transported to the power grid. The water in the reservoir is used many times, and with two units, the energy is converted many times. The high-level reservoir stores a large amount of low-level water, which is equivalent to storing redundant electric energy in the power grid, thus solving the problem that electric energy cannot be stored. Because of the different peak and valley electricity prices, the peak and valley electricity prices are high and the valley electricity prices are low, which greatly improves the economic benefits of pumped storage power stations.
Nanometer comes into our life.
1. What is nano With the repeated efforts of scientists, the word "nano", which was very strange to us a few years ago, now appears frequently in our field of vision. Nanometer is a unit of length. 1 nm is equal to one billionth of a meter, and 20 nm is equal to one third of 1 hair. Since 1990s, scientists all over the world have been engaged in a "nano-war". In the space of 0. 10 to 100 nm, the motion laws and characteristics of electrons, atoms and molecules are studied. 2. China people contributed 1.993. In the Beijing Vacuum Physics Laboratory of Chinese Academy of Sciences, the word "China" was successfully written by manipulating atoms, which indicated that China began to occupy a place in the international nanotechnology field and walked at the forefront of international science and technology. From 65438 to 0998, Tsinghua University Fan Shoushan team made gallium nitride into a bunch of nanocrystals for the first time in the world. In the same year, scientists in China successfully prepared diamond nano-powder, which was praised by international publications as: "Rice straw turns into gold-polycrystalline diamond made of carbon tetrachloride." From 65438 to 0999, the research team led by Professor Xue Zengquan of Peking University assembled single-walled nanotubes on the metal surface for the first time in the world, and assembled the thinnest and best-performing probe in the world. The research led by Dr. Cheng Huiming of Chinese Academy of Sciences has produced high-quality carbon nanomaterials, which is the most convincing achievement in the research field of hydrogen storage carbon nanotubes so far. The research team led by Xie, a researcher at the Institute of Physics, Chinese Academy of Sciences, has developed the world's finest carbon nanotubes with a diameter of 0.5 nm, which is very close to the theoretical limit of 0.4 nm. The research team also successfully synthesized the longest carbon nanotubes in the world, creating "the world's largest with a diameter of 3 mm". In the battle for the theme of "nano", China people frequently appear, especially in the fields of carbon nanotube synthesis, high-density information storage and so on. China's strength should not be underestimated. With the efforts of the scientific community, "nano" is no longer a cold scientific vocabulary. It went out of the laboratory and penetrated into China people's daily necessities. The living environment is becoming more and more environmentally friendly. The washability of traditional coatings is poor. Over time, the wall will become multi-toned. Now there is a new coating with nanotechnology, which not only improves the washability by more than ten times, but also has extremely low organic volatiles, no toxicity, no harm and no peculiar smell, effectively solving the problem that harmful gases cannot be discharged as soon as possible due to the strengthening of building sealing.
Long-term exposure of human body to electromagnetic waves and ultraviolet rays will lead to an increase in various morbidity or affect normal development. Now, high-efficiency radiation protection clothes with nanotechnology-high-tech computer work clothes and maternity clothes have come out. Scientists and technicians mixed nano-sized anti-radiation substances into fibers to make a kind of "nano-clothing", which can block more than 95% of ultraviolet or electromagnetic radiation, and is nonvolatile and insoluble in water, and has long-term anti-radiation ability. Similarly, clothes made of chemical fiber cloth are prone to static electricity due to friction. Adding a small amount of metal nanoparticles in production can get rid of annoying static electricity. White pollution has also encountered a strong challenge of "nano". Scientists use specially developed equipment to crush degradable starch and non-degradable plastics to "nanometer level" and then physically combine them. This new raw material can be used to produce 100% degradable agricultural plastic film, disposable tableware, various packaging bags and other similar products. A large number of experiments of agricultural plastic film for 4 ~ 5 years show that starch is completely degraded into water and carbon dioxide within 70 ~ 90 days, while plastic becomes small particles harmless to soil and air, and also completely degraded into water and carbon dioxide within 17 months. According to experts, this is a substantial breakthrough in completely solving white pollution. From TV broadcasts, books and periodicals, and the Internet, we have learned a little about "nano", and "nano" is also quietly changing us.
How high temperature can people tolerate?
Two British physicists have done the following experiments: they got into the oven to bake bread, and the temperature of dry air in the oven reached 160℃, but they stayed safely in the oven for several hours. This is not a myth, but a true fact. So, what is the truth? It turns out that the two scientists are standing on the mat in the furnace, and they are not in direct contact with the bottom of the furnace or the furnace wall. In fact, they are in dry air. In dry air, people can regulate their body temperature by sweating. When sweat evaporates, it absorbs heat from the air close to the human body, and the temperature of the air around the human body decreases. Therefore, people can live in an environment with relatively high temperature. It is also hot in summer, and we often feel this way. The air is dry, even if the temperature is high, it feels "warm and refreshing"; If the air is humid, it will feel sultry and uncomfortable because it is difficult to evaporate.