1. At the same temperature, frozen pork thaws faster in water than in air. At the same temperature, hot nails cool faster in water than in air. A cup filled with boiling water cools faster when immersed in water than when immersed in air at the same temperature. All these phenomena show that water has better heat transfer performance than air.
2. When the ceiling fan rotates normally, the tension on the suspension point is smaller than that when it does not rotate. The greater the rotational speed, the more the tension decreases. This is because when the ceiling fan rotates, the air has an upward reaction force on the ceiling fan blades. The greater the speed, the greater the reaction.
3. There are several small holes communicating with the outside world on the side of the gas nozzle of the natural gas furnace, but natural gas will not be ejected from the side holes, but only from the nozzle. This is because the air velocity at the nozzle is high, and according to the principle of fluid mechanics, the air surface pressure is lower than the atmospheric pressure outside the side hole, so the natural gas will not be ejected from the side hole of the nozzle.
4. When the pot is filled with cold water, the water droplets attached to the outer surface of the bottom of the pot can only be dried on the flame for a long time, and then they will boil. This is because the water droplets, the pot and the water in the pot keep heat conduction, and the temperature is similar. As long as the water in the pot is not boiled, the water droplets will not boil, and the water droplets will be gradually dried up by evaporation on the flame.
5. Deformable mirror, the farther away from the mirror, the more deformed it is. Because the image in the mirror is formed by the reflection of the silver-plated surface behind the mirror, uneven silver-plated surface or uneven glass thickness will lead to aliasing. The farther away from the deformed mirror, the more the reflected light on the silver-plated surface deviates from the normal position according to the principle of light amplification, and the more deformed the mirror is.
6. Bicycle brake pads: Using the friction principle, the harder the brake is, the greater the friction.
7. Clamping things with chopsticks: The difficulty of clamping things varies with the height of chopsticks (lever principle).
8. Add some oil (lubrication) when the door lock won't open.
9. When people walk, it is very difficult to walk on the smooth ground because the friction of the contact surface is too small; When the car slides uphill, sprinkle some rough stones or straw on the road surface, and the car can move forward smoothly, and increase friction by increasing roughness; Making the sole into various patterns also increases the roughness of the contact surface and friction; Roller skates worn by skaters change sliding friction into rolling friction, reduce friction and increase sliding speed; Lubricating oil is added to all kinds of machines to reduce the friction between gears and ensure the good operation of the machines.
10. Because the object expands with heat and contracts with cold, there should be a gap at the rail joint.
1 1. Sometimes, after pouring a large glass of boiling water from the thermos, the bottle stopper will jump because the cold air outside takes the opportunity to get into the thermos. After the bottle stopper is cooled, the cold air is sealed in the bottle to transfer heat with the hot water. When the temperature of cold air rises, the gas expands when heated, and it will be thrown out of the bottle. At this time, as long as you gently plug the cork and shake the thermos bottle a few times, you can evaporate a lot of water vapor from the boiling water. 7. There is an air layer in the middle of the double-layer glass, so the air is not easy to transfer heat, which can play the role of thermal insulation. Therefore, classrooms are generally equipped with double-glazed windows.
Wait, there are many more, hehe.
I will comfort you when I give you gifts, and I will wear a health service card.