② Fill a plastic coke bottle with half a bottle of water, drill a small hole with a nail at the bottom of the bottle, and you can see the water spouting from the hole. If you let the plastic bottle fall freely at this time, you can see that water is no longer sprayed out. This verifies the weightlessness of water. ① It will be laborious to block the small hole at the front end with your finger and pull the piston outward with your other hand. If the force is stopped, the piston will retreat a certain distance, which verifies the existence of atmospheric pressure.
② Take a syringe, push the piston to the bottom, block the front hole with your fingers, and pull the piston to the middle of the syringe. Then, dip the syringe into the water, remove your finger, and you will see the water enter the syringe. This verifies the principle of the pump-it works by atmospheric pressure. ① Find an iron block, put it on a piece of paper, and pull the paper quickly. You can see that the iron block remains motionless. This experiment can verify that iron has inertia. If you slowly pull the iron block, it can change from static to moving, because the iron block is rubbed, and the visible force can change the moving state of the object.
② With a piece of paper and a cup filled with water, you can do the experiment of "covering the cup" with water and paper, thus verifying the existence of atmospheric pressure.
(3) Make a paper pot with paper, add a proper amount of water and heat it on an alcohol lamp. After a period of time, although the water will boil, the paper pot is not finished, which verifies the conclusion that the water absorbs heat when it boils, but the temperature remains at the boiling point. (1) The hacksaw will make a sound, indicating that the sound is caused by the vibration of the object. If you put the lighted candle next to the vibrating hacksaw bar, you will find that the flame of the candle is shaking, which shows that the sound has energy.
(2) If you press the sawtooth hard, your hand will feel pain, which shows that the force is mutual. If you press the hacksaw bar hard, it can bend or break, which shows that the force can deform the object.
(3) throw the hacksaw forward, hacksaw can continue to fly forward, indicating that the object has inertia. Pushing the hacksaw bar on the table can change it from static to moving, which shows that force can change the moving state of objects. ① Press both ends of the pencil with index finger and thumb respectively, and the indentation depth of the two fingers is different, indicating that the pressure is related to the stress area. Finger pressing the tip of a pencil will also cause pain, indicating that the force is mutual.
② Wrap a thin wire around one end of the pencil or press a thumbtack on one end of the pencil to make it float vertically in water or other liquid. According to the depth of the pencil immersed in the liquid, the density of the liquid can be judged.
(3) The thin metal wire is tightly wound on a round pencil, and then the total width d of n circles of thin metal wire is measured with a ruler, so that the diameter d of the thin metal wire is d = d=D/n n..
④ Connect a small light bulb, a battery and a pencil lead in series with a wire, so that one end of the wire is connected with one end of the pencil lead, and the other end slides on the pencil lead to change the length of the pencil lead connected to the circuit. It was found that the brightness of the light bulb changed. This experiment can explain the working principle of sliding rheostat. Experiment 1
Feel atmospheric pressure
Take an empty aluminum can and a basin of cold water, wrap the iron wire around the mouth of the can and fix it, and twist the iron wire into a handle (with a certain length and strength). Add a small amount of water to the pot, put it on an alcohol lamp and heat it until it boils, and continue heating for dozens of seconds. Quickly (holding the wire handle) pour the cans into cold water and observe the phenomenon.
Note: At this time, the cans are squashed under the action of air pressure, making a loud noise. The experimenter should be psychologically prepared to avoid being burned or even causing a fire when encountering other experimental instruments in a panic. This experiment is dangerous to some extent, so it is suggested to be carried out under the guidance of the teacher.
Experiment 2
Amplitude exchange
Prepare two pendulums with the same pendulum length (the pendulums are heavier) and a thin nylon rope, fix both ends of the nylon rope at high places respectively, and tie the upper ends of the two pendulums in the middle of the nylon rope, and the distance between the suspension points shall not exceed 10 cm (check whether the pendulums are the same when fixing). Put one pendulum in a vertical position, pull the other pendulum to a certain position in the direction perpendicular to the nylon rope (there is no need to have a five-degree angle limit), let it vibrate in the direction perpendicular to the nylon rope, and observe the amplitude changes of the two pendulums (it may take a long time to see, and the required time depends on the device). It can be seen that the amplitudes of the two pendulums will be constantly exchanged.
Experiment 3
Which bottle rolls fast?
Two identical glass bottles, one filled with sand and the other filled with water, slide down the same slope. Which bottle rolls faster? Try it, think about it, why?
Experiment 4
Can the wooden ruler keep level?
There is a wooden ruler with a length of 1 m. Support both ends of the wooden ruler horizontally with the left and right index fingers respectively. At this time, the left and right fingers are close to each other. Can the wooden ruler remain horizontal? What should I do if my left and right fingers are close at the same time? (Hint, related to the knowledge of friction and torque)
Experiment 5
Why doesn't the water overflow?
Pour half a glass of water into the cup and cover it with paper. Press the paper with your palm and turn the cup over. Be careful not to spill the water in the cup. Let go, neither the water nor the paper in the cup will fall. It doesn't matter even if you put some small things like wooden screws in the water. Why is this?
Experiment 6
How to make a simple pendulum swing
Make a simple pendulum with a nylon thread about one meter long and a padlock. You need to blow air to swing it. The swing solution is required to reach about 30 degrees. In this process, the distance between the mouth and the balance position of the simple pendulum should be kept above 0.5 meters, and the body or any other object should not touch any part and suspension point of the simple pendulum. Try to achieve your goal and think about why.
Small electrical experiment
Experiment 1
Try the taste of electrostatic shock.
Wash, rinse and dry the plastic frisbee with washing powder; Prepare a circular iron sheet, slightly smaller than a frisbee, make a small hole in it, tie it with a 20 cm long silk thread through the hole, rub the inside of the disc with a piece of dry fur, and then take it away quickly. Then put the iron sheet into the disc, with one end of the silk thread in your hand (to prevent your hand from touching the iron sheet), so that the charge on the disc will accumulate on the iron sheet, which will be slightly when you approach the iron sheet with your finger. At the same time, you can also see the electric spark and hear the sound of discharge (this is because the voltage is high, but the current duration is short, because the power is small. Although I feel slightly numb, it does not endanger people's life and health)
Note that the effect of this experiment is greatly influenced by the environment. Generally speaking, dry weather is easier to succeed than humid air, and sunny days are easier to succeed than crowded rooms. It is easier to succeed outdoors than indoors.