What are the knowledge points in the first chapter of physics in grade two Want to grade two physics first chapter knowledge

The sound is produced by the vibration of the object. When the vibration stops, the sound also stops. 2. The transmission of sound: the sound is transmitted by the medium. The vacuum cannot transmit the sound. Usually, the sound we hear is transmitted by the air. 3. The speed of sound: the speed of transmission in the air is: 3

Summary table of formula in Volume 2 of junior high school physics
It must be in tabular form

1. Mechanics
Gravity, g = 9.8 N / kg
Density, independent of M, V
pressure
Liquid pressure, only for liquid, h is the depth
speed
The combination of two forces on the same line is "+" in the same direction and "-" in the opposite direction
Archimedes principle, for liquid density, for the volume of the liquid
Merit
power
Leverage balance condition
Mechanical power
2. Thermology
C is the specific heat, t is the initial temperature and t is the final temperature
(combustion), q is the fuel value of combustion
3. Electricity
Current (q is the quantity of electricity)
Resistance (r has nothing to do with u and I, but is determined by their ratio)
Ohm's law
Electric work
(q is electricity, not heat)
electric power
Only when the metal, electrolyte and other conductors conduct electricity can the electric power be calculated
Joule's law
(only for pure resistance circuit)
Series circuit
Parallel circuit

The school used to have a rectangular green belt. Now we want to expand this green belt by 8 meters in length and width, so that the area will be expanded by 200 square meters
After the expansion, we want to fence around the green belt. How long is the fence at least?
Solve by equation

(200/8+8)*2=66
The original rectangle is x in length and Y in width
Now the rectangle is x + 8 in length and y + 8 in width
(x+8)(y+8)-xy=200
8(x+y)=200-64=136
x+y=17
The original perimeter = 2 (x + y) = 2 * 17 = 34
Now perimeter = 2 (x + 8 + y + 8) = 66
The fence is at least 66 meters long

In the triangle ABC, the opposite sides of the angles a, B and C are a, B and C respectively. If ∠ C = 2 / 3 π, ABC forms an arithmetic sequence, and the tangent tolerance is 2
(1) Find C

(1) According to the cosine theorem, we get C & # 178; = A & # 178; + B & # 178; - 2abcosc (a + 4) ^ 2 = (a + 2) & # 178; + A & # 178; + a (a + 2) a ^ 2 + 8A + 16 = a ^ 2 + 4A + 4 + A ^ 2 + 2a8a + 16 = 2A ^ 2 + 6A + 42a ^ 2-2a-12 = 0A ^ 2-a-6 = 0 (A-3)

Given (x + my) (x + NY) = x & # 178; + 2xy-8y & # 178;, find the value of (M + n) Mn

（x+my)(x+ny)=x²+(m+n)xy+mny²=x²+2xy-8y²
∴(m+n)=2
mn=-8
（m+n)mn=2*(-8)=-16

Xiaohong's height is 135 cm, Xiaojuan's height is 150 cm, Xiaojuan's height is higher than Xiaohong______ %．

(150-135) △ 135, = 15 △ 135, ≈ 11.1%; answer: Xiaojuan is 11.1% higher than Xiaohong

What is the surface tension of water

0.5x+1.5x=15.6 16x+4-9x=25 39.6-3x=3.24×5．

（1）0.5x+1.5x=15.6， 2x=15.6， 2x÷2=15.6÷2， x=7.8；（2）16x+4-9x=25， 7x+4=25， 7x+4-4=25-4， 7x÷7=21÷7， x=3；（3）39.6-3x=3.24×5， 39.6-3x=16.2， 39.6-3x+3x=16.2+3x， 3x+16.2=39.6，3x+16.2-16.2=39.6-16.2， 3x÷3=23.4÷3， x=7.8．

The length of a machine part is 4 mm. How many centimeters should be drawn on a drawing with a scale of 20:1? The length of a machine part measured on a drawing with a scale of 1:200 is 4 mm. What is the actual length of the part

4x20 = 80mm
=8Cm
4X200=800mm=O.8m

Ask a primary school math fill in the blanks
The base angle of an isosceles triangle is 60 ° and its top angle (it is a () triangle).

The base angle of an isosceles triangle is 60 degrees, its apex angle is 60 degrees, and it is an equilateral triangle
or
The base angle of an isosceles triangle is 60 degrees, its apex angle is 60 degrees, it is a (regular) triangle
Concept: an isosceles triangle with an internal angle of 60 ° is an equilateral triangle

What are the knowledge points in the first chapter of physics in grade two Want to grade two physics first chapter knowledge