I urgently need a physics experiment report for my first year of junior high school

buoyancy is gone".

Do the little test below.

Equipment. Find a container with a flat bottom, let a candle head adhere to the bottom of the container, and then pour water into the container, the candle head will not float; Gently flip the candle head over and it will float instantly.

It can be seen that when the object is in close contact with the bottom of the container, there is no liquid seeping between the two contact surfaces, and the lower surface of the object is no longer subjected to the upward pressure of the liquid on it, and the liquid loses its upward support force, and the buoyancy disappears with it.

Now, can you come up with measures to get the submarine out of trouble?

How is buoyancy generated?", the student's conclusion that "buoyancy is the difference between the upward and downward pressure of a liquid on an object" is understandable, but it is difficult to believe, so doing a good experiment on the disappearance of buoyancy is the key to overcoming this difficulty, and the following two easy methods are introduced.

Method 1] Equipment: 1 glass funnel of appropriate size (available in the chemistry laboratory), 1 ping pong ball, and a glass of red water.

Steps: 1) Intentionally push the ping pong ball into the water, and the ping pong ball will float quickly after letting go.

2) Hold the funnel with your hand (the bell mouth is facing up, and the funnel handle is sandwiched between the middle finger and the ring finger), put the table tennis ball into it, press and hold the table tennis ball with your thumb, pour water into the funnel, release the thumb, and it can be seen that the table tennis ball does not float, (at this time, there is water flowing down from the lower mouth of the funnel handle, this is because the table tennis ball and the funnel are not very tight).

3) Plug the water outlet with your fingers, you can see that the water surface in the funnel handle is gradually rising, and when the water surface rises to the table tennis ball, the table tennis ball will quickly float up. (If the water comes out too quickly from the lower mouth of the funnel handle, you can pad a circle of cotton at the contact between the table tennis ball and the funnel, so that you can calmly observe the water rising in the funnel handle.) )

Method 2] Equipment: a transparent flat-bottomed plastic bucket (about 10cm in depth, the diameter should be larger, easy to operate), a wooden block with a basically flat bottom surface (such as chess pieces, building blocks, thermos stoppers, etc.), a chopstick, and a cup of water.

Make a small hole bucket: take an iron skewer and burn it red on the alcohol lamp, wear a small hole on the bottom surface of the plastic barrel, with a hole diameter of about 1cm, and grind the hole edge with sandpaper to form a small hole bucket.

Steps: 1) Intentionally dip the wooden block into the water, and the wooden block will float up quickly after letting go.

2) Put the wooden block into the bucket with the flat side down and cover the hole, press the wooden block with chopsticks and pour water into the bucket. Remove the chopsticks, and you can see that the wooden block does not float. (At this point, there is water dripping down at the hole, because the contact surface between the block and the barrel is not very tight).

3) Plug the small hole with your fingers, and the wooden block will immediately float up.

In view of the fact that the surface of the object cannot be absolutely smooth in practice, the above two examples cleverly use the "small hole leakage" to prevent the water from remaining under the object, so that the object loses the upward pressure of the liquid, and thus loses its buoyancy. Then step (3) magically reproduces the buoyancy, which makes the students feel more excited and eager to try.

Students observe and solve problems on their own.

In addition to the above two exceptions, you can also refer to [Data Collection] - the content of experimental data for experiments on the disappearance of buoyancy.

We only studied physics in the second year of junior high school.

1. Experiment name: Measure the speed at which the paper piece falls.

2. Experimental design ideas:

The experimental equipment provided by the experiment "Measuring the Speed of Falling Paper" includes a tape measure, a stopwatch, and a piece of paper, but using these experimental equipment, it is always found that the paper is floating left and right in the process of falling, and the falling route is not straight, and it is easy to touch the desk or other objects and change the route. I wanted to find something to replace it, and at first I wanted to use a balloon, but I found it more difficult to control the route, and the balloon was too big to be placed on the lab table to attract the students' unintentional attention. Later, I thought that this kind of thing should still be made of paper, because if you use something with a high density such as iron balls, the falling time is too short to measure, or the measured time error is too large.

Finally, I discussed with my classmates the idea of replacing the original piece of paper with a "paper cone" composed of three paper strips that I played with when I was a child. Moreover, the time of the fall can be measured by a stopwatch (since there are not enough tape measures in the laboratory, the time of the fall is about 1 2 seconds, taking advantage of the known condition of human height).

3. Purpose of the experiment:

Learn to measure the velocity of moving objects.

Fourth, the scientific principles involved in the experiment:

The measurement of the velocity at which a piece of paper (changed to a "paper cone") falls, the experimental principle used is the velocity formula. The main reason for changing the paper piece to a "paper cone" is that the air flow rate is different due to the shape of the lower part when it falls, and according to the Bernoulli principle, "in a fluid, the higher the flow velocity, the lower the pressure" (Bernoulli's principle), which causes the "paper cone" to rotate clockwise or counterclockwise when it falls (the specific direction of rotation is determined by the order in which it is installed).

5. Experimental operation steps:

1) Before the experiment, the height of the classmate should be measured, and the height s of the "paper cone" should be recorded in the experiment**.

2) One student put a 30 50 cm long scale flat on top of his head, and the other student released the "paper cone" freely according to such a height, and at the same time began to record the time, and recorded the time t when the "paper cone" landed, and recorded it in the experiment**.

3) Repeat the above steps twice.

4) According to the velocity formula, calculate the speed at which the "paper cone" falls three times, and calculate the average value.

6. Experimental apparatus or**:

Students can make their own "paper cones" (cut three identical strips of paper, fold each strip of paper in half once, and then put them together in a loop, as shown in Figure 1, and pull the three "feet" outward, as shown in Figure 2).

7. Equipment used in the experiment:

A paper cone, a 30-50 cm long scale, and a stopwatch.

8. Experimental effects and other issues that need to be explained:

Experimental effect: Around December 14, 2005, the teaching effect in the 22 classes of Nanjing Shuren International School was very good, which solved the shortcomings of the original paper unstable, the route is not straight, and the distance can not be measured, and the experimental equipment is easy to make, low cost, simple to operate, and students are interested. Later, it was further tested in the teaching of physics in the second year of junior high school in other schools in Gulou District, and the unanimous response of all peers was good.

It has great promotion and use value.

1] Experimental utensils: seeds, cassette, cotton, plastic boxes, chopsticks, wires, water cups, flower pots, etc. of 5 kinds of plants.

2] Purpose of the experiment: ** The necessary conditions for seed germination, and the process of seed germination was observed.

III] Experimental Procedure:

1. Seed selection and preparation: Zhengsun used the seeds of soybeans, mung beans, red beans, corn and peas to carry out germination experiments. The reason is these five.

The seeds are easy to obtain, germinate quickly, and the phenomenon is obvious, among them, soybean, mung bean, red bean, and pea are dicot plants, and the first three are unearthed germination, pea.

Beans germinate in the soil; Corn is a monocot. Germination experiments with these seeds can be used to observe different germination clusters. All dry (or new mold chains.

Fresh) seeds were placed in water (as long as they were not at high temperature) for 24 hours before the experiment.

1. Tie a few fine holes at the bottom of a beverage bottle, and then add an appropriate amount of water to the beverage bottle, at this time, you will find that there is water flowing out at the bottom of the bottle, which can confirm that the liquid has pressure on the bottom of the container. Continue to quickly fill the bottle with water and tighten the cap, at which point no water can be seen coming out of the bottom of the bottle. If you loosen the cap again, you will find that the water has flowed out.

This indicates that this phenomenon is formed by atmospheric pressure.

2. Take another empty drink bottle and fill it with water, tighten the flat cap, and then heat a steel needle with an alcohol lamp. Gently scald a fine hole on the lower side wall of the beverage bottle (note that do not squeeze the beverage bottle too hard when scalding the hole). When the hole is pierced, you will find that there is no water flowing out, and at the same height of the first hole, you will find that there is still no water flowing out after scalding a fine hole at any position.

This is due to the action of atmospheric pressure and proves that atmospheric pressure is present in all directions, in contrast to the liquid pressure characteristics. After scalding the top two holes again, it is found that the lower holes are flowing outward, while the upper holes do not flow to the reed, and air enters the inside and above of the bottle. If you unscrew the cap of a beverage bottle, you will find that all three holes will run water.

And the closer the hole is to the bottom of the bottle, the farther the water will be sprayed with a column.

3. Take another drink bottle and fill it with water and tighten the cap, put it upside down in a glass sink with enough water, unscrew the cap in the water, grab the bottle and lift it up, but find that the water in the bottle does not fall back into the sink without revealing the water surface. (You can change to a taller bottle for a "comparative experiment" to lay the foundation for the introduction of the Torricelli experiment.) On the basis of this experiment, you can also punch holes in the bottom of the bottle and immediately see the water in the bottle flowing back into the sink.

The reason is that there is atmospheric pressure inside and outside the bottle that cancels each other out, and the water column flows back to the sink under the action of its own gravity.

Fourth, you can also choose cans, do not pull the lid all open, the opening should be as small as possible. After pouring the drink, use a hair dryer to heat the can at a high temperature for a period of time, and then seal the pull mouth with plasticine to ensure that there is no air leakage. Then pour cold water on the can, and you will hear the sound of the can being pressed and deformed, and at the same time you will see that some parts of the can are deflated.

It shows the thermal expansion and contraction of gases, and also proves the existence of atmospheric pressure.

About measuring the volume of an irregular object.

Equipment. Wood.

Steps; The first;

The volume of the part of the wood immersed in water can be obtained by placing wood in water and measuring the rise of the water surface, or by placing it in a full graduated cylinder and measuring the volume of the overflowing water.

The wood is then cut along the horizontal plane, removed, and the mass of the underwater part is measured with a balance.

Its density is calculated by renting in the formula.

The mass of the entire object is then measured overall.

By vm p

The full volume is calculated.

Second; Take a measuring cup, the water surface is level with the cup surface, find a way to immerse all the wood in the water (such as pressing it into the water with a thin needle), and weigh the volume of the overflow water.

The third; If the container is cylindrical, fill it with water, and then put the object in the water, the volume of the object is the volume of the object in the hollow part of the branch or vessel

The area of the cylinder and the base area are high.

If the object does not sink, tie an iron block to the object and put it in the water, measure the volume of the iron and the object, and then measure the volume of the iron block, and then subtract the volume of the iron block from their total volume to get the volume of the object

Phenomenon; Included in the steps.

Conclusion; Derive the volume of the wood.

Read the physics book by yourself, observe the phenomena, processes, and answer the physical meaning of the formula.

【Objective】The density of milk was measured with a balance and a graduated cylinder.

Experimental principle] = m v.

Experimental materials and equipment] milk, balances, weights, measuring cylinders, beakers.

Experimental Methods (Procedure)].

1.Place the balance on the water platform and adjust the balance balance according to the rules for using the balance;

2.Add an appropriate amount of liquid to the beaker, weigh the total mass m1 of the liquid and the beaker with a balance, and record it in the pre-designed **;

3.Place the graduated cylinder on the water platform, pour the liquid in the beaker into a part of the graduated cylinder, read the number and write down the volume v of the liquid in the graduated cylinder;

4.Weigh out the mass m2 of the beaker and the liquid remaining in the cup, and record it in **;

5.According to =(m1-m2) v, the density of the milk is calculated;

6.In order to ensure the accuracy of the measurement, multiple measurements can be taken (generally not less than 3 times), and the average value can be taken as the measurement result.

Precautions] Be careful when pouring and pouring out liquids so that they do not overflow. Otherwise, it will cause measurement errors.

Record**] omitted.

I hope it helps you, and if you have any questions, you can ask them

I wish you progress in your studies and go to the next level! (*

Dissolution of kitchen spices.

Experimental Objectives: To understand the dissolution degree of various edible seasonings in waterExperimental equipment: salt, flour alkali, sugar, chicken essence, Sichuan pepper, large ingredients, six identical cups, balances, and chopsticks.

Experimental process: pour the same volume of water into six cups, weigh out 20 grams of the required reagent with a balance, release them into cups with water, and stir evenly with chopsticks.

Experimental phenomenon: there was no obvious change in the cup with salt, soda and sugar, and there was no solid precipitation at the bottom of the cup; The color of the cup in which the chicken essence is put is yellowish, and there is no solid precipitation; Put it in a cup of peppercorns, which does not dissolve and float on water, and put it in a cup of large ingredients, which does not dissolve and sink to the bottom of the water.

Experimental results: most of the powdered solids are dissolved in water, and most of the bulk solids are insoluble in water.