Air is the best insulator, and of course it can't transfer heat.However, if a part of the air is heated to a certain extent, the temperature will rise, and the expansion will be quite large, it will also rise upward, causing the same convection phenomenon as water, and the heat will also go elsewhere.
The sun radiates a lot of heat on the ground. Where the ground is directly exposed to the sun, the temperature rises. The air in contact with this part starts this upward movement, causing the surrounding cold air flow to fill the gap, forming the daily wind.Due to the existence of convection, the air mixture is unusually uniform.In the summer sun, the roof sways in the distance. This is because the convection of the air causes the light to twist in it.[2]
Air convection experiment
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Demonstration Experiment (I)
1. Fabrication method
As shown in Figure 1, buckle an enamel bowl onto the asbestos mesh.Use a fan-shaped transparent plastic film to stick a funnel, and stick its small mouth on the outside of the bottom of the bowl with a strong adhesive to seal it.Then, a glass tube with a length similar to the height of the funnel shaped film cylinder and a diameter about half of the diameter of the bottom of the bowl, a triangular pipe rack tied with iron wire, is vertically placed in the funnel shaped film cylinder.
2. Usage
Light the alcohol lamp under the asbestos mesh and heat the enamel bowl. The hot air density is small, and it will rise along the glass tube. The dense cold air on the funnel flows downward to supplement.To display theConvection phenomenonPut a piece of goose down into the funnel. The goose down will flow to the bottom of the funnel with the cold air, and then rise along the glass tube with the heated air. After leaving the nozzle, it will float to the bottom of the funnel with the cold air at the top of the funnel. This cycle is endless, vivid and interesting.[3]
Figure 1. Air convection demonstrator
1. Experimental materials
Two 500ml drip bottles (one with a metal cover and the other without), 12 # iron wire 1.5m, glass tube with a diameter of 2.4cm 15cm, square seat bracket, a tripod, a glass funnel, an asbestos mesh, an alcohol lamp, and a little fluff of chicken, duck, and goose (can be dyed with color).
2. Production method
Intercept the drip bottle (take the upper part of the cone), wrap it with wool for 1-2 circles at the 450m scale, coat it with alcohol or gasoline and ignite it. While burning, rotate the drip bottle. When the drip bottle is evenly heated, immediately insert it vertically into the cold water, and the bottle can be disconnected neatly along the wrapping.The cross section of the conical part can be polished.
Intercept the central tube: measure 15cm on the waste test tube with a diameter of 2.4cm and use the above method to intercept.
Making iron wire ring: make 12 # iron wire into two iron rings with a diameter of 2cm, and one iron ring with a diameter of 2.4cm. The length of welding clip reserved for the iron wire is 12cm (two), 1cm (one).
3. Usage
After assembly as shown in Figure 2, the iron wire ring, the glass bottle mouth and the glass tube can be fixed with universal glue, the alcohol lamp is lit, and the dyed wool is placed from the lower hood edge.Through demonstration, the convection phenomenon of air can be observed with the help of fluff movement.[4]
