Question 1: in the madeburg hemispherical test, two hollow copper balls with a diameter of 20cm were put together, the air inside was extracted, and two teams of horses were used to pull the two hemispheres in the opposite direction. If a pair of horses could produce a pull force of 1600n, it would take eight pairs of horses to pull the hemispheres apart, so as to find the local atmospheric pressure at that time? Question 2: Xiaogang's mother bought a box of milk and put it on the floor. The contact area between the box and the floor is 0.025 square meters. The total weight of the box and the milk is 5kg. The packing bag of each bag of milk in the box is marked with the words "net content 221ml 227g" (10 g) (1) What's the density of this milk? (2) What is the pressure of the milk on the floor?

Question 1: in the madeburg hemispherical test, two hollow copper balls with a diameter of 20cm were put together, the air inside was extracted, and two teams of horses were used to pull the two hemispheres in the opposite direction. If a pair of horses could produce a pull force of 1600n, it would take eight pairs of horses to pull the hemispheres apart, so as to find the local atmospheric pressure at that time? Question 2: Xiaogang's mother bought a box of milk and put it on the floor. The contact area between the box and the floor is 0.025 square meters. The total weight of the box and the milk is 5kg. The packing bag of each bag of milk in the box is marked with the words "net content 221ml 227g" (10 g) (1) What's the density of this milk? (2) What is the pressure of the milk on the floor?

1. The cross-sectional area of copper ball is:
3.14 * 20 * 20 = 1256 square centimeter = 0.1256 square meter
The tensile force is:
1600*8＝12800N
The pressure is as follows
12800 / 0.1256 = 1.019 * 10 ^ 5 (Pascal)
2. Density = mass / volume
＝227/221
＝1.027
Pressure = pressure / stressed area
＝5000*10/0.025
＝2*10^6

A solid cube with a side length of 0.1 meters on the horizontal table top of 1 square meter weighs 8 Newtons. A cylindrical container B (excluding its own weight) contains 5 kg of water and has a bottom area of 200 square centimeters
Put the cube into B, how much pressure does B exert on the table (the water does not overflow)

There are a lot of data here, but not all of them are useful. Some of them are useless, "1 square meter horizontal desktop"
"Solid cube with side length of 0.1M"
Here is the definition of pressure!
Pressure = pressure / stressed area
P=F/S=（8+5*10）/0.02=2900Pa
The mass of water is converted into weight

As shown in the figure, when the object is pulled by the pulley block to move at a constant speed on the horizontal ground, the pulling force F = 20n. If the weight of the rope, the weight of the pulley and the friction between the rope and the pulley, as well as the friction between the wheel and the shaft, are not taken into account, the amount of friction on the object is______ N. Direction______ ．

The fixed pulley can only change the direction of the force, so the pulling force of each section of the rope acting on the moving pulley is 20n, that is, the object is pulled 40n horizontally to the right through the moving pulley; because the object moves in a uniform linear direction, the friction force on the object is 40n horizontally to the left

How to design the conversion experiment of kinetic energy and potential energy

Junior high school
The experiment was carried out with roller
Hang both ends of a roller with equal length rope, and then wind the rope on the shaft. After releasing the hand, the wheel turns, and the potential energy is converted into kinetic energy
high school
Heavy hammer experiment of dot timer
Measure the height and speed of the object with a dot timer, and verify it with kinetic energy

Is there any conversion between kinetic energy and potential energy in the experiment which is related to the size of potential energy?

Gravitational potential energy: EP = MGH {EP: gravitational potential energy (J), G: gravitational acceleration, H: vertical height (m) (from zero potential energy surface)} electric potential energy: EA = q φ a {EA: electric potential energy (J), Q: electric quantity (c), φ A: electric potential (V) (from zero potential energy surface)} law of conservation of mechanical energy: Δ e = 0 or EK1 + EP1 = E

The second grade physics experiment
Only for the physics knowledge of the second year of junior high school, it doesn't need to be too complicated. The materials should be easy to find and write clearly!

To make fruit battery: tools and materials: 3 lemons (lime can also be used) & 3 bright copper coins. We use coins, 3 galvanized screws (other active metals can also be used, not necessarily zinc, as long as it can be replaced) & 4 wires, the best

Junior two physics experiment
It must be a very simple experiment from last semester

Test 1
Name: Rubber Band Guitar
Materials: several rubber bands of different thickness, one carton, two wooden strips
Production method: put the wooden strips on both sides of the carton and bind the rubber bands with different thickness on the carton and wooden strips regularly
By comparison, is the tone of a tight or relaxed rubber band high? Is it a thick rubber band or a thin rubber band high?
Can you use the experimental results to explain: "why can string instruments such as Hu Qin and violin make different tones?"
Test 2
One coke bottle, one rigid plastic straw
Make a hole in the cap of the coke bottle to just insert the straw. After the cap is closed, the lower end of the bottle is as close as possible to the bottom of the bottle, and a section of it leaks out,
Seal the joint between the straw and the bottle cap (I glue it with 2 seconds)
Open the bottle cap, fill in half a bottle of water, tighten the cap, blow air into the bottle, the bubbles gather above the water in the bottle, increase the pressure of the closed air, the mouth breaks away from the straw, and water will be ejected from the bottle through the straw
It shows that air pressure exists, which is also the principle of spray.
Reference: the bigger the bottle, the easier it is to succeed

Measure the length of objects and find some exercises
I'm not familiar with this, so I'll find some questions like this to write
For example, 1.502m = 1502mm. If you measure with a millimeter scale, the reading should be 1.5020m and 3mm long. The reading is 3.0mm. If you use centimeter as the unit, it is 0.30cm. If you use meter as the unit, it is 0.0030m. By the way, I'll give you some explanation

This kind of question is called the question of giving points, and you don't need to do too much practice. Just understand it. You can find the rules in the questions you give: for example, if an object is 3 mm long, the reading is 3.0 mm. Why add a 0 after it? Because this 0 is the number to be read. What's the situation to be read? For example, the object you measure is beyond 3 mm, but less than 4 mm, if you read 3 mm, I think it's too short, so you think that the object should be in the range of 3. Mm. Then, this number is the estimated number. This number can be in the range of 0-9, whatever you choose. Of course, the closer the better

What's the sound
Sound is produced by the vibration of objects. Different objects make different sounds. Take two examples

1) When you move the rubber band, the finger's force is large, the rubber band's vibration amplitude is large, and the volume is strong; when you move the rubber band, the finger's force is small, the rubber band's vibration amplitude is small, and the volume is weak
(2) If you fold the rubber band in half (half the original length), use the same force to tighten it, and then move the rubber band, from the two comparisons, you will find that: in the first phenomenon, the rubber band vibrates slowly, and the sound is low; in the second phenomenon, the rubber band vibrates fast, and the sound is high

Reflection exercises of physics light in grade two of junior high school
A ray of light shoots from right to left on a horizontal plane mirror at an incidence angle of 30 degrees. If the direction of the incident ray is kept unchanged and the mirror rotates 10 degrees clockwise, what is the angle between the reflected ray and the incident ray?

The incident angle of 30 ° is the angle between the incident light and the normal. Because the normal is perpendicular to any interface, the angle between the incident light and the plane mirror is required at first, which is 90-30 ° and 60 ° respectively