A summary of solving physics formula in junior high school

A summary of solving physics formula in junior high school

Physical quantity unit formula name symbol name symbol mass m kg kg m = PV temperature T centigrade ° C velocity v m / S v = s / T density p kg / M & sup3; kg / M & sup3; P = m / V force (gravity) f Newton (cow) n g = mg pressure P Pascal (PA) P = f / s work

Junior high school physics all unit conversion
For example, what is the negative quadratic power of 10?
There is also the unit conversion which is often used to calculate the pressure

The - 2 power of 10 = 0.01
The - 3 power of 10 = 0.001
That is, the negative power of 10 is one of the positive power of 10, OK?
1. Length unit conversion:
1km = 1000M
1 m = 10 decimeters = 100 cm
1 cm = 10 mm
1 mm = 1000 μ M
M -- meter
DM -- decimeter
Cm -- cm
Mm -- mm
2. Time unit conversion: 1 year = 365 days, 1 day = 24 hours, 1 hour = 60 minutes, 1 minute = 60 seconds
3. Speed unit conversion: 1m / S = 3.6km/h
4. Conversion of mass units: 1kg = 1000g, 1t = 1000kg, 1g = 1000mg
5. Volume unit conversion: 1 cubic meter = 1000 cubic decimeter, 1 cubic decimeter = 1000 cubic centimeter
6. Density unit conversion: 1g / cm3 = 1000kg / m3
7. Area unit conversion: 1 square meter = 100 square decimeter, 1 square decimeter = 100 square centimeter
1 sq cm = 100 sq mm
8. Power unit conversion: 1kW = 1000W
9. Current unit conversion: 1A = 1000mA, 1mA = 1000 microampere
10. Voltage unit conversion: 1kV = 1000V, 1V = 1000kV
11. Resistance unit conversion: 1 megohm = 106 ohm, 1 kiloohm = 1000 ohm
12. Electric work unit conversion: 1 kwh = 3600000j
13. Frequency unit conversion: 1 MHz = 106 Hz, 1 kHz = 1000 Hz

Praise the teacher's poem, about 50 words
Do not "four times of spring wind, several times of autumn rain to wash the gap. Black hair accumulated frost, weaving sun and moon, chalk speechless to write spring and autumn. Silk spit out, spring is not old, candle tears become ash, autumn is thicker. Spring sows peach and plum three thousand garden, autumn is full of fruits." want others

Praise the teacher poem 1: four times of spring breeze, several times of autumn rain wash the gap. Black hair accumulate frost, weave the sun and moon, chalk speechless to write spring and autumn. Silk spits out, spring is not old, candle tears become ash, autumn is thicker. Spring sows peach and plum three thousand garden, autumn is full of fruits

The top and bottom surfaces of the frustum are R1 and R2, and the length of the generatrix is L. it is known that R1: R2: l = 2:1:3, and the side area of the frustum is 81 π. Find R1 R2 L

The top and bottom arc lengths are 2 π R1 and 2 π R2 respectively, and the chord length is L
Then the sector area is 1 / 2 * (2 π R1 + 2 π R2) * L
∵r1:r2:l=2:1:3
The sector area = (2 π R2 + π R2) * 3 * R2 = 81 π, R2 = 3
Then R1 = 6, l = 9

Given that the side area of the frustum is s, the radii of the upper and lower bottom surfaces are R1 and R2, the side area of the cone of the frustum is obtained

The ratio of the side area of the cone to that of the truncated cone is R1 ^ 2: R2 ^ 2
Let the side area of the cone of this frustum be X
Then (X-S): x = R1 ^ 2: R2 ^ 2
The solution is x = R2 ^ 2 * s / (R2 ^ 2-r1 ^ 2)

If the radius of the top and bottom surfaces of a cone is R1 R2, what is the radius of its inscribed sphere
Such as the title
Can you make it clear
Why right triangles? A little proof
Angular bisector theorem

The radius of the sphere = √ (R1 * R2). Draw a plane graph. The two vertices of the generatrix and the center of the sphere are right triangles

Calculation formula of cone volume

Let R be the radius of the upper bottom, R be the radius of the lower bottom, and H be the height
Then v = (1 / 3) * π * h * (R ^ 2 + R + R ^ 2)

What is the formula for the volume of a cone?

The volume formula of frustum v = 1 / 3 * π * H (R ^ 2 + R + R ^ 2)
In fact, the cone is equivalent to a large cone, cut off the top of the small cone
Volume of cone: v = 1 / 3 * π * h * R ^ 2
Suppose that the bottom radius of the cone is r, the top radius is r, and the height is h; then the volume of the large cone is assumed to be V1 = 1 / 3 * π * H1 * R ^ 2; the volume of the small cone is assumed to be V2 = 1 / 3 * π * H2 * R ^ 2, obviously R: r = H2: H1; the volume of the small cone is assumed to be V2 = 1 / 3 * π * H2 * R ^ 2;
Then v = 1 / 3 * π * (H1 * r * r-h2 * r * r)
Substitute r = R * H2 / H1 into v = 1 / 3 * π * ((H1 ^ 3-h2 ^ 3) / H1 ^ 2) * R ^ 2
Use the cubic difference formula v = 1 / 3 * π * (h1-h2) * ((H1 ^ 2 + H1H2 + H2 ^ 2) / H1 ^ 2) * R ^ 2
= 1/3 * π * h * (1+h2/h1+h2^2/h1^2) * R^2
Then substitute R * H2 / H1 = r into the above formula v = 1 / 3 * π * H (R ^ 2 + R + R ^ 2)

The volume formula of cone
Can you write the formula and analyze it in detail,

Method 1. A frustum can be regarded as a figure obtained by a right angled trapezoid rotating around the height perpendicular to the bottom edge. The volume can be calculated by integral method. I won't repeat it here. If you are interested, you can study multiple integral by yourself
Method 2. Universal quadrature formula: v = 1 / 6 × (s upper + 4S middle + s lower) × H
Where s is the area of upper bottom, s is the area of middle section, s is the area of lower ground

Calculate the volume formula of the frustum!

Let R be the radius of the upper bottom, R be the radius of the lower bottom, and H be the height,
Then the volume calculation formula of frustum v = π * h * (R ^ 2 + R + R ^ 2) / 3