Experiment 1: Pick up coins skillfully.
1. Experimental equipment: a flat chassis, a cup, a candle, a coin and boiling water.
2. experimental purpose: put a little water and a coin into a flat chassis, and the coin is completely immersed in the water. It is required to try to take coins out of the plate by hand without wetting your hands.
3. Experimental methods:
Method 1: light a small candle, put it on a plate filled with water and coins (the candle and coins should be placed at a certain distance), then bring an empty cup, turn the cup upside down, slowly cover the candle flame for about one minute, then quickly buckle it into the plate and buckle the candle. You can immediately find that the flame of the candle will soon go out. Then I soon found that the water in the plate was sucked into the cup. After about two minutes, the water in the plate was basically sucked into the cup, and the coins outside the cup were completely out of water. I got the coin as easy as blowing off dust.
Experimental analysis: the reason why water is sucked into the cup must be because the pressure in the cup is less than the atmospheric pressure outside the cup. What is the relationship between the candle burning in the cup and the pressure reduction in the cup? Is the temperature change causing the pressure to decrease or the oxygen consumed during combustion causing the pressure to decrease? I did another experiment.
Method 2: Also add water and coins to the plate. Fill the cup with freshly boiled water, let it stand for 2 minutes, and heat the cup. After pouring the boiling water out of the cup, I immediately put the cup upside down on the plate (don't buckle coins). Immediately found that there will be bubbles in the cup, but soon disappeared. After about 5 minutes, the cup cooled down and the water in the plate was sucked into the cup, so that I could catch the coin easily without getting my hands wet.
Experimental analysis: the cup must absorb water because the pressure in the cup decreases. Through the above two experiments, I understand that the reason why the pressure in the cup becomes smaller is that lighting candles or heating the cup with boiling water raises the temperature of the air in the cup and drives out the hot air in the cup. After a few minutes, the cup naturally cools, which reduces the temperature of the air in the cup, but the volume remains unchanged, which reduces the pressure in the cup. Due to the pressure difference between the inside and outside of the cup, the water outside the cup is sucked into the cup.
As for the process of candle burning, although oxygen is consumed, carbon dioxide and water vapor are produced at the same time, so the consumption of oxygen is not the cause of pressure reduction.
Experiment 2: A small steel needle floats on the water.
1. experimental equipment: a glass of water, a small steel needle, a small piece of paper, a chopstick and a small magnet.
2. Experimental purpose: Let the small steel needle float on the water.
3. Experimental method: put a small piece of paper in a glass of water, then put a small steel needle on the small piece of paper by hand, and slowly immerse the small piece of paper in the water with chopsticks. You can find that the small piece of paper sinks to the bottom of the cup, but the small steel needle is still floating on the water, and then shake the magnet on the outside of the cup, and the small steel needle moves to the side.
4. Experimental analysis: The specific gravity of small steel needle is 7.6 times that of water, but it can float on the water. Why? It turned out that the small steel needle touched by hand produced a thin oil layer on the surface. Although the small steel needle floats on the water, it does not directly contact with the water, but lies on a thin oil surface. Due to the gravity of the small steel needle, the oil surface is pressed into a concave surface, and the concave surface has an upward supporting force for the small steel needle. Coupled with the buoyancy effect of water on the small steel needle on the oil surface, the balance of the two forces enables the small steel needle to float on the water surface without sinking.
Experiment 3: Please try to stand up!
1. experimental method: sit in a chair by yourself, but keep the upper body and legs perpendicular to the thighs. You can't lean forward or move your feet. Please try to stand up.
2. Experimental results: No matter how hard you try, you can't stand up as long as you keep this posture unchanged.
3. Experimental analysis: What caused this? It turns out that the balance of an object can only be achieved when the vertical line hanging from its center of gravity does not intersect with its bottom surface. If a person sits in a chair according to the experimental requirements, the vertical line hanging from the center of gravity will inevitably not pass through the area between his feet, that is, the "bottom". Unless you move your feet under the chair, or lean forward, that is, move the "bottom" backward or move the "center of gravity" forward, so that the vertical line hanging from the center of gravity can pass through the "bottom", people can never stand up.
Experiment 4: Distinguish raw eggs from cooked eggs.
1. experimental purpose: how to distinguish the raw and cooked eggs simply and conveniently without breaking the eggshell?
2. Experimental method: Take one raw and cooked egg, put it on the flat chassis and rotate it with your fingers. Cooked eggs turn fast for a long time; While raw eggs rotate unsteadily and slowly. When the rotation stops, raw eggs and cooked eggs are different. When the cooked egg rotates, it will stop immediately as long as the finger resists slightly, while the raw egg will continue to rotate for a while after applying resistance with the finger and letting go.
3. Experimental analysis: When the egg rotates, the cooked egg has become a solid whole, while the raw egg cannot rotate immediately because of its liquid yolk and egg white and the relative position with the eggshell is not fixed. Due to inertia, these liquid substances hinder the rotation of eggshells, and egg yolk and egg white play a "brake" role here. When the rotation stops, the phenomenon of raw eggs is still explained by the inertia of internal substances. Although the eggshell has stopped spinning, the liquid inside is still spinning. As for boiled eggs, because they are already solid substances, they will stop turning immediately if there is a little resistance.
Although these small experiments are simple to do, they contain rich physical knowledge, which makes me learn and consolidate a lot of scientific knowledge while experiencing fun.
In life, we also need this spirit of exploring scientific knowledge, so that knowledge can enrich our brains, science can be more integrated into our lives, and interest can be more embellished in our lives.