The sound made by sparse teeth is low, and the sound made by thin teeth is high. The sound generated by the comb can be amplified by the "horn" of the paper roll or something hard.
Experiment 2 compares the difference between vibration and sound with a water cup.
In order to enhance comparability, you can only use a cup or a bottle-instruct students to tap the mouth of the cup with a small wooden stick in the process of adding water to the cup to compare different sounds. Experimental results-With the increase of water in the cup, the sound becomes lower and lower. Tip: In order to prevent bubbles from forming in the process of adding water, it is best to use cold boiled water. )
In experiment 3, the vibration phenomenon of * * * was observed with the materials around us.
To use two cups, first add one-third of water to one cup, and tap the mouth of the two cups with a pencil to see if the two cups make the same sound. Then slowly add water to the second cup (knock on the mouths of both cups at the same time) until the two cups make the same sound (at this time, the two cups reach the state of * * * vibration). Then, stick a metal wire to the mouth of the second cup with tape, and knock on the mouth of the first cup, and you will find that the metal wire is vibrating gently. As you keep knocking, make the cup with wire slowly close to the first cup, you will find that the vibration amplitude of the wire is getting bigger and bigger until it finally falls. (Related story: A long time ago, a czar's army went out to train. With the officer's orders, the soldiers marched in neat steps. When the troops were walking on a wooden bridge, the wooden bridge suddenly shook up and down and finally collapsed with a bang. After inspection, it was found that the collapse of the wooden bridge was caused by the marching rhythm of the soldiers. From then on, the army crossed the bridge and never dared to March forward with neat steps. )
Experiment 4: Make a "tape recorder" with the materials around you.
Active materials: jar (or round paper box) without cover, round paper, glue, nails, thick iron wire, thin iron sheet with tip, long glass and candles.
Activity steps:
(1) Cut off the bottom of the can with a suitable tool, and the can becomes a short and thick cylinder.
(2) Cut a round piece of paper and stick it on one end of the can with glue instead of the cut bottom.
(3) After the glue is dry, spray paper with water.
(4) Punch two small holes with the same height on the side of the cylinder with nails.
5] Insert the wire into the shape shown in the figure with a vice and insert it into the two holes.
[6] When the bottom of the paper is soaked with water and becomes dry and tight like a drum skin, drop a drop of glue in the center of the paper, stick a thin iron sheet (one end of the iron sheet is as sharp as a needle) on the glue, and set it aside until it is dry.
Once, light a candle and bake the glass on the flame until the glass turns black.
⑻ Turn the glass rod over and put the blackened side on the table.
(9) Bring the cylinder to the front so that the tip of the iron sheet just reaches the blackened glass plate.
⑽ Pull the glass sheet and observe the movement track left by the needle tip on the blackened glass sheet. (Corresponding to the different sounds made by the surrounding objects, the needle tip will leave different tracks. In order to avoid recording confusion, a blackened glass plate should be changed every experiment, and the sound should be controlled one at a time. )
Test the life of seeds.
There are many ways to test whether seeds are alive, and it is certainly possible to germinate them. however
The easiest way is to see if it is breathing. There are several ways to test the respiration of seeds. Here you are.
Introduce a kind of.
Find a big glass bottle, which contains some dried soybean, corn or wheat seeds, accounting for about three.
A roll. Put an open small glass bottle on the top of the seed, which is filled with caustic soda (sodium hydroxide).
Solution. Plug the bottle with a cork or rubber stopper, make a hole in the stopper and install a curved one.
Glass tube or transparent plastic tube. Wipe between the bottle stopper and the bottle mouth, as well as the contact between the glass tube and the plug hole.
Vaseline avoids air leakage. Insert the other end of the test tube into the water cup and drop a few drops of red ink in the water.
The water turned red. Do not touch it after installation. After a few days, you will see red water rising along the glass tube.
What is the truth?
We know that seeds breathe by absorbing oxygen in the air and exhaling carbon dioxide.
It absorbs oxygen from the air in the bottle and releases carbon dioxide. However, it releases less carbon dioxide.
The alkali solution in the bottle was absorbed. Therefore, the air density in the whole bottle becomes smaller and the pressure decreases. this
In the sample, the air pressure in the big bottle is less than the outside air pressure, and the water in the cup rises along the glass tube. this is
It means that the seeds in the bottle are alive.
Dry seeds, the breath is very weak, generally speaking, the vitality is more lasting and moist.
Seeds breathe vigorously and lose their vitality easily. In addition, temperature also has a direct impact on the life of seeds.
High temperature and short seed life; Low temperature leads to long life of seeds. The seed life of different plants is also different.
The same. For example, when the seeds of weeping willows mature, they can germinate only within 12 hours. And some plants.
The life span of seeds is very long, such as the ancient lotus seed found in Pulandian, Liaoning, China, with an estimated life span of 1000.
In fact, it germinated and grew in Beijing Botanical Garden.
Conditions of seed germination
The life activities of seeds have not stopped, but they are too weak to be noticed. If the seeds meet,
Under suitable environmental conditions, it will gradually develop into a seedling, which is called germination.
Under what conditions will it germinate?
Find three cups, put a small piece of tape on each cup and mark the number. Put 10 in each of the three cups.
A kidney bean seed. 1 no water, no 2 cup with half a glass of water, no 3 cup with water.
Don't drown all the beans, so leave it until the end of the experiment.
Results Kidney beans in No.3 cup germinated smoothly, which indicated that kidney beans needed water, air and humidity to germinate.
The right temperature.
Do seeds need sunlight to germinate?
Find two plates, put some wet sand, and mix dozens of grains of wheat in each plate. Put one
One plate is placed on the balcony, and the other plate is covered with a porcelain basin or a black box to keep the wheat moist until it is full.
The inspection is over.
As a result, you will find that seed germination has little to do with sunlight, because seed germination needs camp.
There is no need for photosynthesis to improve nutrients from the internal storage of seeds, so there is no need for sunlight.
Of course, this is not the case. According to the characteristics of some seeds, they germinate worse in the dark.
Some.
(Pro Yan Hui Lu Jinsong)
Up and down
First put four newly germinated seeds on a piece of paper with good water absorption, and then gently put them away.
Sandwiched between two pieces of glass, tied with a thin thread. Put the glass with germinated seeds on the balcony.
In the pot, the seeds get water and continue to develop into seedlings. Then turn the glass in one direction every three days.
In the basin. After several turns, you will find that the roots of the seedlings always grow downwards and the stems and leaves always turn downwards.
Grow on the ground.
This shows that plants have the characteristics of directional movement, which is related to the great attraction of the earth.
(Yu, Lu Jinsong)
Roots that do not grow downward
Put the corn seeds on the wet sandy soil layer, and keep the appropriate temperature and humidity conditions. As the seeds grow,
When planting the root of 1-2 cm, two plants are selected, and the roots are placed horizontally, one of which is
The top of the corn root was cut off. After a few days, you will find that the roots that have not been cut automatically bend down and grow.
The roots with the top removed seem to have lost their way and grow straight along the horizontal direction.
The root of a plant is geotropic, which means that it can "feel" the stimulation of gravity, so it is placed horizontally.
The roots will bend down automatically. The "headquarters" for feeling and controlling this characteristic of roots is the root crown.
The crown secretes auxin according to the change of gravity direction to control the bending direction of roots. Therefore, root cap 1
Once removed, the roots will not bend downward.
(Cai Qingyuan)
Xiangguang
In the process of development and growth, under the influence of sunlight, plants will grow in the direction of sunlight.
We call it phototropism.
Plant morning glory seeds in a small flowerpot, and put them in a shoe box after they germinate and grow into seedlings. flower pot
Near the side of the shoe box. A partition wall was made of cardboard in the box, leaving a gap on the other side.
Open a small window. Cover the box and put the shoe box on the balcony. In a week, the morning glory plants will grow up.
Stick your head out of the window.
It turns out that there is an auxin in plant cells that is very sensitive to light and controls the hair of plants.
As long as there is a little light in the box, this auxin will work.
(Yu, Lu Jinsong)
Leaf water evaporation experiment
Cut four leaves of the same size from a rape, and paint vases on the cut of the petiole.
Lin. Then mark the four leaves with the numbers 1, 2, 3 and 4 respectively, mark them with cards and fix them on the line.
First, the upper and lower surfaces of 1 blade are coated with vaseline, and the upper surface of No.2 blade is coated with vaseline.
Lin, the lower surface of No.3 blade is coated with vaseline, and No.4 blade is not coated with vaseline. Finally, use it.
The petioles of four leaves are hung in a ventilated place with burning lines.
The results showed that after 2-3 days, the leaves of 1 were bright green, as if they had just grown from the stem of rape.
Cut off the same. No.2 leaf, only the upper surface of the leaf is coated with vaseline, so the leaf is yellow. The third leaf
Vaseline is only coated on the lower surface, and the leaves are bright green, such as the new second and third leaves, because the surface is coated.
The surface is different, so there is a big difference. No.4 leaf is not coated with vaseline, and the whole leaf has withered.
The yellow has shrunk. The difference between 1 and No.4 leaves is even greater.
Please use what you have learned about how plants drink water. Do it with your hands and think with your brain. this
What scientific truth does this experiment show?
(Yang Guo)
Water drops in the bag
Find a potted plant and soak the soil in it. Cover the plants with a big transparent plastic bag.
Tie the mouth of the bag tightly with a thin thread. Move the flowerpot to the sun, and after a while, a promise will appear on the inner wall of the plastic bag.
Small drops of water.
We can rule out that water enters the bag from the mouth of the bag, so the only possibility of water droplets in the bag is
It is the leaves and branches of plants. It turns out that there are many pores on the epidermis of leaves, which will drain water from plants.
When it is discharged into the air, the branches of plants will also evaporate a small amount of water, which we call transpiration. It can promote
Make the root system absorb water and promote the transportation of water and nutrients to all parts of the plant.
(Yu, Lu Jinsong)
Roots absorb water
Choose a carrot, wash it, and dig a hole 2-3 cm deep at the top with a knife.
Cave. Rinse the small hole with water to remove impurities in the hole. Fill the holes with 1 parts.
A syrup made of water and two parts of sugar. Drop a little ink into the syrup to make it red or blue.
Plug the small hole with a perforated foam block and insert a transparent straw in the hole. Cut off the bottom of the root with a knife.
Finally, it makes it easier for water to pass through the exposed tissues of the roots. Put the roots in a glass filled with water, and after half an hour.
You can see the juice rising slowly along the straw.
This experiment is enough to prove that roots absorb water.
(Yu, Lu Jinsong)
Transfer water with sugar
Cut off the top of the apple and dig an inverted cone hole with a knife to make a cone hole.
The top of the apple is open, just at the other end of the apple. Hang the apple with the big mouth up and the small mouth down.
Pay attention to the opening at the bottom of the apple. There is no water flowing out for a long time.
At this time, if you sprinkle sugar (or salt, etc.). ) Even in the cave, you will see the cone immediately.
Water magically appears on the surface. Water gradually gathered at the bottom, blocking the opening. About 20 minutes,
A crystal clear water drop naturally falls. Since then, water has been oozing, flowing and dripping.
Do you know why sugar can absorb water? There is a little water in the apple hole. Sprinkle sugar on it.
On the surface, sugar melts to form a high concentration solution. Because the concentration of apple cell sap is very low, so
Water permeates from low-concentration apple cell sap into the sugar solution outside, and then gathers into a "water flow".
(John Chan)
The role of cells
Take two big potatoes and boil one of them in water for a few minutes. Then put two potatoes on it.
Cut a piece from the top and bottom, dig a hole in the middle of the top, and put some sugar in each hole.
Then stand them upright in a plate filled with water. A few hours later, the hole in the raw potato was filled with water.
Boiled potatoes or sugar granules.
The cells of raw potatoes are alive. They are like a small hole that allows water molecules to pass through the water in the plate.
Through the potato wall and into the hole. Boiled potato cells are destroyed, so there is no osmotic function.
Please taste the water in the potato plate. Is it sweet? No. Why is sugar in raw potatoes?
The water did not enter the plate, but the secret was on the cell membrane. The cell membrane of potato is like a sieve, which is only allowed to be very small.
Particles passing through the sieve holes cannot pass through the sieve holes. The molecules of white sugar are relatively large.
You can't cross the cell membrane, so the water in the dish is not sweet. Knowing this, you can give flowers and trees.
When applying fertilizer, never use too thick fertilizer water, otherwise, the water in plants will flow back into the soil.
Make plants wither and even die.
(Apotheker)
White flower discoloration
Prepare a clean glass bottle, pour half a bottle of red ink, and then cut off plants with leaves and white flowers.
Branches placed in a bottle in the sun will turn red in half an hour.
Take out the branch and cut it horizontally with a blade. Some red dots can be seen on the cross section.
If you cut the stem vertically, you can see some red lines, which are called vascular bundles.
Tube bundles are used to transport water and nutrients. The branches of plants are inserted with red ink because of the steaming of leaves and petals.
The red ink will gradually extend into the veins and petals from bottom to top.
(Yu, Lu Jinsong)
a hydroponic flowers
People like to plant a pot of daffodils in winter, because daffodils don't need people's careful care, just casually.
Put its bulb in a shallow pot, and in a few days it will grow delicate green leaves and give birth to beautiful fragrance.
Flowers.
Other plants, such as onion bulbs, carrot bulbs and arrowhead bulbs, can also enter.
Culture in water.
Choose fresh onions with beautiful appearance and moderate size, wash them and use two thin sticks or bamboo shreds.
Put the onion rack across the mouth of the cup, then pour in clear water to immerse a small part of its stem in the water.
The cup moved to the balcony.
After a few days, onions can grow long roots and green leaves.