A phenomenon related to electrical knowledge
1. Rice cookers, electric woks and electric kettles all use electric energy to convert into internal energy, and all use heat transfer to cook, cook and boil water.
2. The exhaust fan (range hood) converts electric energy into mechanical energy, and air is converted by air convection.
3. Insert the three-pin plug of the rice cooker, electric frying pan and electric kettle into three hole socket to prevent electric leakage and electric shock.
4. The microwave oven has the advantages of uniform heating, high thermal efficiency and no pollution. The heating principle is to convert electric energy into electromagnetic energy, and then convert electromagnetic energy into internal energy.
The electric light in the kitchen works by converting electric energy into internal energy and light energy by the thermal effect of current.
6. Kitchen stoves (honeycomb coal stoves, liquefied gas stoves, coal stoves and wood stoves) convert chemical energy into internal energy, that is, fuel burns to release heat.
Second, phenomena related to mechanical knowledge.
1, the spout and belly of the electric kettle form a communication device, and the water surface is always flat.
2. The thin edge of the kitchen knife is to reduce the stress area and increase the pressure.
3, the blade of the kitchen knife has oil, in order to cut vegetables when the contact surface is smooth, reduce friction.
4. The handle, spatula handle and electric kettle handle have convex and concave patterns, which make the contact surface rough and increase friction.
5, fire shovel to send coal, is to use the inertia of coal to send coal into the furnace.
6. Pour boiling water into the thermos bottle and know the water level according to the sound. Due to the increase of water volume, the length of air column decreases, the vibration frequency increases and the tone increases.
7. Keep watering when grinding the kitchen knife, because the heat generated by the friction between the kitchen knife and the stone increases the internal energy of the knife, the temperature rises, the hardness of the knife edge becomes smaller, and the knife edge is unfavorable; Watering is to use heat transfer to reduce the internal energy and temperature of the kitchen knife without rising too high.
Third, phenomena related to thermal knowledge.
(a) Phenomena related to thermal expansion and heat transfer.
1, use the stove to boil water or stir fry, and let the bottom of the pot be placed on the outer flame of the flame, and don't let the bottom of the pot press the burner, because the temperature of the outer flame of the flame is high, which can make the temperature of the pot rise rapidly.
2, spatula, spoon, colander, aluminum pot and other cookware handles are made of wood, because wood is a poor conductor of heat, so it will not heat up during cooking.
3. The purpose of installing an exhaust fan above the cooker is to speed up air convection, so that kitchen fumes can be discharged in time to avoid polluting the space.
4. The hot casserole is easy to break on the wetland. This is because casserole is a bad conductor of heat. When the casserole is placed on the wetland, the outer wall of the casserole shrinks quickly, and the temperature of the inner wall drops slowly. The casserole shrinks unevenly inside and outside and is easy to break.
5. When the thermos bottle is filled with boiling water, it can be better insulated without it. Because there is a layer of air in the bottle mouth when it is not filled, it is a bad conductor of heat, which can better prevent heat loss.
6. Cooking mainly uses heat conduction to transfer heat. Cooking and boiling water mainly include
Heat is transferred by convection.
7. Pour some boiling water from the thermos in winter. When you cover the cork tightly, you often see the cork jump up at once. This is because when boiling water is poured out, some cold air enters, and after the cork is plugged, the cold air enters expands rapidly when heated, and the pressure increases, thus pushing the cork away.
8. Hot soup that just came out of the pot in winter, I saw that there was no heat in the noodle soup, as if the soup was not hot, but it tasted very hot because of the soup.
There is a layer of oil on the surface to prevent heat loss (water evaporation) in the soup.
9. In winter or when the temperature is very low, pour boiling water into the glass, and preheat the glass with a small amount of boiling water first, so as to avoid the excessive temperature difference between the inside and outside of the glass, and the thermal expansion of the inner wall is hindered by the outer wall, resulting in the glass breaking.
10. Boiled and scalded eggs are easy to shell when soaked in cold water for a while. Because hot eggshells and protein contract when they are cold, the degree of contraction is different, so they are separated.
(2) phenomena related to the state change of objects
1. Liquefied gas is compressed and liquefied at room temperature, and then put into a steel tank; When in use, liquefied gas is decompressed by the pressure reducing valve, changed from liquid to gas, and then enters the stove for combustion.
2. Boil water in a soldering iron pan, and the pot won't burn out. If you don't fill it with water, put it on the fire for a while and it will burn out. This is because at standard atmospheric pressure 1, the boiling point of water is 100℃ and the melting point of tin is 232℃. When boiled with water, as long as the water is not dry, the temperature of the pot will not obviously exceed 100℃, and it will not reach the melting points of tin and iron, so the pot will not burn out. If water is not put on the fire, the temperature of the pot will reach the melting point of tin in a short time, the solder will melt and the pot will burn out.
3. When boiling water or cooking food, the sprayed steam burns more seriously than hot water or hot soup. Because when steam turns into hot water or soup with the same temperature, it will release a lot of heat (liquefaction heat).
4. Cook food in a casserole. After the food is cooked, let the casserole leave the stove, and the food will continue to cook in the pot for a while. This is because when the casserole is out of the oven, the temperature at the bottom of the casserole is higher than 100℃, while the food in the pot is 100℃. After leaving the furnace, the food in the pot can absorb heat from the bottom of the pot and continue to boil until the bottom temperature drops to 100℃.
5. Cook food faster in the pressure cooker. Mainly to improve the air pressure in the pot and the boiling point of water, that is, to improve the temperature of cooking food.
6. In summer, a lot of "sweating" on the wall of the tap water pipe is often a sign of rain. The "sweating" of water pipes is not the water leakage in the pipes, but the water pipes are mostly buried underground and the water temperature is low. When the water vapor in the air contacts the water pipe, it will release heat, liquefy into small water droplets and attach to the outer wall. If there is a lot of "sweating" on the pipe wall, it means that the water vapor content in the air is high and the humidity is high, which is a precursor to rain.
7. Cooking food is not as fast as it gets hotter. Because the temperature of water remains unchanged after boiling, even if the firepower is increased, the water temperature cannot be raised. As a result, it can only accelerate the evaporation of water, make the water in the pot evaporate and waste fuel. The correct way is to boil the water in the pot with a big fire, and then keep the water boiling with a small fire.
8. After the water in the kettle is boiled in winter, you can see the "white gas" at a certain distance from the spout, but you can't see the "white gas" near the spout. This is because the temperature near the spout is high, and the water vapor from the spout cannot be liquefied, but the temperature at a certain distance from the spout is low; The water vapor ejected from the spout gives off heat and liquefies into small water droplets, that is, "white gas".
9. When frying food, splashing water droplets will hear the sound of "beep, beep" and spill oil. This is because the boiling point of water is lower than that of oil and the density of water is higher than that of oil. The water droplets splashed in the oil sink to the bottom of the oil and quickly heat up and boil, and the bubbles generated rise to the oil surface and make a noise.
10. When the temperature of the pot is high, sprinkling some water into the pot will make a "cheep, cheep" sound and release a lot of "white gas". This is because water evaporates quickly, then liquefies and makes a "cheep, cheep" sound.
1 1. When the soup boils and overflows the pot, quickly add cold water to the pot or scoop up the soup, which can reduce the temperature of the soup to below the boiling point. Add cold water. The temperature of cold water is lower than that of boiled soup. After mixing, cold water absorbs heat and soup releases heat. In the process of raising soup, because the air is lower than the temperature of soup, the soup releases heat and the temperature decreases. After pouring into the pot, it absorbs heat from the boiling soup, reducing the temperature of the soup in the pot.
(3) phenomena related to molecular thermal motion in thermodynamics
1. Pickled vegetables often take half a month to become salty, while salt is added for a few minutes when cooking. This is because the higher the temperature, the faster the ion movement of salt.
2. In the corner where coal has been piled for a long time, if you scrape a thin layer from the wall with a knife, you can see that it is black inside, because it is divided.
The child never stops doing irregular movements. In the corner of the coal pile for a long time, because the coal molecules diffused into the wall and scraped off a layer, the inside was still black.
In daily life and production, we can improve our ability to observe, analyze and solve physical problems by carefully observing the physical phenomena around us and connecting with the physical knowledge we have learned.
In the kitchen, if we pay attention to cookers, utensils and some phenomena in cooking and frying, we will find that many places need to use physical knowledge.
1. When porridge or rice is hot or cold, the pot makes a beep, beep, and bubbles keep popping up, but once it is tasted, porridge or rice is not hot. Why?
Heating cold porridge or rice is different from boiling water. Although water is a bad body of heat, its conduction speed to heat is very slow, but its fluidity is very good. The water at the bottom of the pot will expand when heated, float when the density becomes smaller, and the surrounding cold water will flow over to fill it. Through this convection, the heat at the bottom of the pot will be continuously transferred to all parts of the water, making the water hot. Cold porridge or cold rice has poor fluidity and is not easy to conduct heat. Therefore, when the porridge or rice at the bottom of the pot absorbs heat, the temperature rises rapidly, but it cannot flow up or around quickly. A lot of heat is concentrated at the bottom of the pot, and the porridge at the bottom of the pot is burnt. Because the heat is difficult to transfer to the porridge, the porridge on it is still cold. When heating cold porridge or rice, add more water to the pot to make porridge thinner and enhance liquidity. In addition, it is necessary to stir frequently and force convection, so that porridge can be heated evenly.
Secondly, when using casserole to cook the meat or cook soup, when the soup is boiled and removed from the stove, the soup will continue to boil for a while, but this phenomenon does not exist in wok and aluminum pot. Why?
Because the casserole is made of clay, and the specific heat of nonmetal is much larger than that of metal, and its heat transfer ability is much worse than that of metal. When the casserole is heated on the stove, the outer temperature of the pot is much higher than 100℃, and the inner temperature is slightly higher than 100℃. At this point, the pot absorbs a lot of heat and stores a lot of heat energy. After the casserole is taken out of the oven, the outer layer of the pot which is much higher than 100℃ will continue to transfer heat to the inner layer, so that the soup in the pot can still reach 100℃ and continue to boil for a period of time, so that the iron aluminum pot will not appear this phenomenon (please analyze the reasons yourself).
Third, the "cooked" in fried meat. On holidays, some people always fry a few meat dishes, so how to fry the meat slices? If the meat slices are directly put into a hot oil pan and stir-fried, the water contained in the lean fiber will quickly evaporate, making the meat slices dry and hard, and even frying the meat, greatly losing its flavor. In order to stir-fry the sliced meat delicious, chefs often mix the sliced meat with a proper amount of starch in advance. After the meat slices were put into the hot oil pan, the water in the starch paste attached to the meat slices evaporated, but it was difficult to evaporate the water in the meat slices, which still kept the freshness of the raw meat and reduced the loss of nutrition. The meat is almost cooked, which means "cooked as soon as we meet" The sliced meat fried in this way is fresh, tender, delicious and nutritious.
4. What is the best way to thaw frozen meat? Take out the frozen meat and chicken from the refrigerator, how to thaw it?
It is best to use cold water close to 0℃. Because the temperature of frozen meat is below 0℃, if it is thawed in hot water, the frozen meat absorbs heat from hot water, and its outer layer is thawed quickly, so that the temperature rises to above 0℃ rapidly. There is a gap between the meat layers, which reduces the heat transfer ability, making it difficult for the frozen meat inside to absorb heat and thaw, forming a hard core. If frozen meat is put into cold water, the temperature of cold water will drop to 0℃ because of the heat absorption of frozen meat and frozen chicken, and some water will freeze. Because 1g water can release 80 calories when it is frozen (while 1g water can only release 1 calorie when it is lowered to 1℃), after frozen meat absorbs so much heat, the temperature of the outer layer of the meat rises rapidly, while the inner layer is easy to absorb heat, so the temperature of the whole meat also rises rapidly to 0℃. Repeat this several times and the frozen meat can be thawed. From the point of view of nutrition, this method of uniform and slow heating is also scientific.
Why is the sky red in the morning and evening?
Colorful clouds often appear on the horizon around sunrise and sunset in the morning and evening. The morning glow and sunset glow are caused by the scattering of light by air. When sunlight enters the atmosphere, it will scatter when it meets atmospheric molecules and particles suspended in the atmosphere. These atmospheric molecules and particles themselves do not emit light, but because they scatter sunlight, each atmospheric molecule forms scattered light.
Source. According to Rayleigh scattering law, light with shorter wavelength such as violet, blue and cyan in the solar spectrum is most easily scattered, while light with longer wavelength.
Red, orange, yellow and other colors have strong light transmission ability. So we see that the clear sky is always blue, while the light above the horizon is only yellow, orange and red with longer wavelengths. After these rays are scattered by impurities such as air molecules and water vapor, the sky there will be colorful.
Color. As the saying goes, "Don't go out at dawn, travel thousands of miles at sunset", that is to say, there is a bright red sunrise in the morning, indicating that there are many water drops in the atmosphere, which indicates that the weather will turn to rain. If there is a fiery red or golden sunset glow, it means that there is no cloud in the west, and the sunlight can be transmitted to form a sunset glow, which indicates that the weather will be fine.
The Dead Sea will never disappear.
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 wheels are pressed on the ground.
The greater the resistance, 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 a 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 move forward 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. this