Interesting scientific experiment. Tell me about it.

(1) Cut a small piece from the hard foam block with a knife and process it into a circle (about φ 4 mm in diameter). In the bottle cap of a beverage bottle, first fill half the bottle cap with water, and put a small foam plate in the center of the bottle cap. At this time, you will see the small disc moving slowly from the middle of the cover to the edge. Near the edge, the small wafer accelerates to the edge and tries to climb the cover wall. Finally, a part of the small wafer is in the water, and a part is on the cover at the joint of the water and the cover wall (exposing the liquid level). If you use a toothpick to "push" the small disc into the water in the middle of the bottle cap, it will still accelerate its movement towards the lid wall and try its best to climb up the lid wall. No matter how "push", it will not help. As shown in figure1a.

(2) Continue to add water into the bottle cap until it "piles" into a convex surface. At this time, you will see the small disc move to the convex center of the water in the bottle cap. It is difficult for you to push it to the edge of the bottle cap with a toothpick. When you push it to the edge, just loosen the toothpick and it will immediately accelerate back to the center of the bottle cap and stop in the water, as shown in figure1b.

The reason for the above phenomenon is that the small wafer is subjected to surface tension in water. The liquid surface is similar to a taut rubber film. If the surface of a liquid is curved, it tends to flatten. Therefore, the concave surface exerts a pulling force on the liquid below, and the convex surface exerts a pressure on the liquid below. Under the action of these surface tensions, the light-weight wetted object (relative to water) appears the above phenomenon.

(3) Under the action of surface tension, the surface of liquid tends to shrink to the minimum, and the surface area of spherical objects is the smallest among all kinds of objects with the same volume. Soak a piece of paper in melted paraffin solution (or vegetable oil) (change it into wax paper or oil paper), and drop water drops on wax paper (or oil paper). The shape of larger water droplets is flat, which is due to the influence of gravity. For small water droplets, the influence of gravity is far less than that of surface tension, and the water droplets are static.

It is spherical. You can also do the experiment in (2) above after dropping water drops on waxed paper, oiled paper or painted desktop.

In our daily life, we will see the interface between the wall of a water container without a lid and water, and the interface between the wall of a teacup and tea. After a few days, the reason why dirt appeared on the interface was due to the surface tension of the liquid.

2 a cup of "level 3"

(1) Take a 35OmL transparent plastic beverage bottle and cut off 2/3 to make a water cup. Put (waste red candle) into an evaporating dish and heat it into liquid (be careful not to get too high). Put the processed small cup obliquely, pour the candle liquid into the small cup, and then pour it out, so that the wall of the cup is "plated" with a layer of wax, and the width from the bottom of the cup to the mouth of the cup is about 1cm.

(2) Experiment: When water is poured into the above-mentioned "special" water cup, it can be seen by naked eyes that the water surface of the "waxed" part is convex at the wall of the cup, while the water surface of the non-waxed part is concave, with a height difference of about 2mm, and the water surface of the central part of the cup is horizontal.

(3) Inspection: If the "small disc" is placed on the water surface in the central part of the cup, the "small disc" will basically not move, indicating that the water surface in this part is basically horizontal, as shown in Figure 2 (A). Push the small wafer onto the wall of the wax-plated cup and let it go, then the small wafer will move to the center of the cup, as shown in figure 2, B. Slowly push the small disc to the wall of the cup without waxing. When it is close to the cup wall, it can be seen that the small disc quickly moves close to the cup wall and sticks to the cup wall, as shown by C in Figure 2.

The reasons for the above three situations are as follows: for the beverage cup, water is an immersion liquid, and the liquid level near the cup wall bends upward because of water immersion in the beverage cup, so the small disk moves closer to the cup wall; For the paraffin "plated" on the beverage cup, water is not a liquid, and the liquid level near the cup wall bends downward, so the small disk should move to the center of the cup; The water surface in the center of the cup is basically horizontal, so the small disk basically does not move.