What is Newton's law of motion? The content of the three laws

What is Newton's law of motion? The content of the three laws

Newton's law of motion is the first law of motion, which was summarized by Sir Isaac Newton in the 17th century and published in the mathematical principles of natural philosophy

All formulas of thermodynamic laws, including conditions

The ideal gas law: PV = NRT, V is the molar volume, that is v / n
The relationship between heat capacities: CP = CV + R, γ (specific heat and specific capacity) = CP / CV
The first law of Thermodynamics: Du = DQ + DW, W is the work done by the external force on the system,
∵w=-∫fdl=-∫pSdl=-∫pdV
∴dU=dq-pdV
∵ q is a function of T, so u can be expressed as a function of T and V
For ideal gas, CT is zero, for real gas, CT is very small
That is, Du = cvdt is constant
dU=0,pdV=dq
Δ q = ∫ (process 1 to 2) PDV = ∫ (process 1 to 2, default to follow all) RTDV / v = RT * ln (V2 / V1) = RT * ln (P1 / P2)
DV = 0, that is, DW = 0
Du = DQ = cvdt, then integral
dp=0
dq=dU+pdV=CvdT+d(pV)=CvdT+RdT=CpdT
(it can be directly understood that when the pressure is constant, the temperature directly determines the input heat energy.)
dq=0
dU=dw=-pdV=CvdT
∴-RTdV/V=CvdT
∴-RdV/V=CvdT/T
∴-R∫dV/V=Cv∫dT/T
∴R*ln(V1/V2)=Cv*ln(T2/T1)
∴(V1/V2)^R=(T2/T1)^Cv
(V1 / V2) ^ (γ - 1) = T2 / T1
∵T=pV/R
(V1 / V2) ^ γ = P2 / P1, that is, P1 * V1 ^ γ = P2 * V2 ^ γ, PV ^ γ = constant,
Then we get the relationship between the changing pressure and the changing volume
New definition: H (enthalpy) = u + PV
∵dU=dq-pdV
∴dU+d(pV)=dq+Vdp,dU+d(pV)=d(U+pV)=dH=dq+Vdp
New quantities are defined: DS (entropy) = DQ / T, △ s = ∫ DQ / T
The second law of Thermodynamics: spontaneous process △ s > 0, reversible process △ s = 0
It is used to judge whether it is a spontaneous process
∵△S>0
When the temperature is constant, for example, the chemical reaction in an airtight container
DS > DQ / T, (at constant temperature, ∫ DQ / T = 0)
The DQ TDS is obtained by the transformation

There should be a formula
A gaseous system, u = 2.5pv + constant
The system starts with state a: P = 0.2 MPa, v = 0.01 M & # 179;, and then goes through the following three processes
State a to state B: isobaric expansion to 0.003m & # 179;
From state B to state C: P changes linearly with V until P = 0.5 MPa, v = 0.01 M & # 179;
State C to state a:
Calculation: 1) calculate the values of Q and W in the three processes
2) Calculate the Q and w values in the process of state a to B, and meet P = 10 ^ 5 + 10 ^ 9 (v-0.02) ^ 2

PA = 0.2MPa, VA = 0.01M & # 179;, Pb = PA, VB = 0.03m & # 179; (the original data is wrong, estimated as the value), PC = 0.5MPa, VC = 0.01M & # 179;. 1) w (AB) = - PA (vb-va) = - 0.2 * 10 ^ 6 (0.03-0.01) = - 4 * 10 ^ 3 J Δ U (AB) = ub-ua = 2.5pbvb-2.5pava = 2.5 * 0.2 * 10 ^ 6 (0.03-0.01) = 1

On the calculation formula of gas internal energy under certain conditions (thermodynamics basis)
Q = (I + 2) / 2nr △ t?
E = I / 2nr △ t?
My question is under what circumstances is (I + 2) why?
This problem should not be long, I hope not to copy

This should be the endothermic formula, CP = CV + r = I / 2 + r = (I + 2) R / 2
Q = CP △ t = (I + 2) / 2nr △ t?
Q = CV △ t = I / 2nr △ t?

The first time to measure the sound speed in cast iron was carried out by the following method. When one end of the cast iron pipe was knocked, the sound could be heard twice at the other end of the pipe. The first time was from the cast iron pipe, and the second time was from the air. The length of the cast iron pipe was 931 meters, and the interval between the two sounds was 2.5 seconds What is the propagation speed of the iron pipe?

The propagation time of sound: t air = SV air = 931m340m / s ≈ 2.74s, from the Title Meaning: t air - t cast iron = 2.5s, the propagation time of sound in cast iron: t cast iron = t air - 2.5s = 2.74s - 2.5s = 0.24s, the propagation speed of sound in cast iron V cast iron = st cast iron = 931m0.24s ≈ 3879m / S

Summer night, a dazzling lightning 8 seconds after the thunder, thunder lasted for 5 seconds to stop, the discharge of the cloud and how many meters away from you?

The distance between cloud and human is s = VT = 340m / s × 8s = 2720m A: the distance between cloud and human is 2720m

How to calculate the speed of sound

There are two methods
1. Wave speed = distance / time
2. Wave speed = wavelength / period

Teach me how to calculate the speed of sound!
I learned the speed of sound for the first time, and taught me to calculate the speed of sound from scratch,

Theory is easy, practice is difficult
Let me tell you a relatively simple method. You know the starting gun. You ask a person to shoot a gun at a distance of 500 meters (the farther the more accurate it is). When you see the white smoke when shooting, you start timing (sound begins to spread). When you hear the sound of the gun, you stop timing. Then divide the time by 500 meters, which is the local sound propagation speed at that time
The speed of sound in the air is 340 meters per second (25 degrees Celsius)

Is the speed of sound in ice fast or in water fast? Why?
It is said that the speed of sound in solid is higher than that in liquid, so the speed of sound in ice is higher than that in water. It is also said that the speed of sound in dense medium is fast, so the speed of sound in water is higher than that in ice. I am puzzled, please give me some advice!

Why is the speed of sound the fastest in solids? Textbook:Liquids and solids are less compressible than air,and that makes the speed of sound in those media higher than in air.
The propagation velocity of wave depends on the characteristics of medium. For example, the propagation velocity of elastic wave depends on the inertia and elasticity of medium. Specifically, it depends on the density and elastic modulus of medium
Shear, volume and long-term elastic deformation can be produced in solid, so shear related shear wave and longitudinal wave can be transmitted in solid
Just like a row of people passing a small ball from point a to point B, if the number of people is large and the distance between people is very close, the speed of transmission will be fast. If the number of people is small and the distance between people is far, the speed of transmission will slow down. The mechanical wave propagation of sound wave also depends on the density of particles in the propagation medium, and there are few particles between two points, The transfer of energy (like the movement of the ball mentioned above) is slower. Among solids, liquids and gases, the density of solids is generally the highest and that of gases is the lowest. Therefore, the propagation of sound waves is the fastest in solids and the slowest in gases
That is, the propagation speed is related to the medium density, and the sound speed is faster when the density is high
The relationship between sound speed and temperature in air: v = 331 × root sign (1 + T / 273) (M / s) t: temperature in centigrade; V: speed of sound at t ℃. The relationship between sound speed and temperature is also introduced: sound speed is also the speed of sound, that is, the speed of sound propagating in medium. Sound wave can propagate in solid, liquid or gas medium, and the higher the medium density is, the higher the medium density is, In the air, the speed of sound varies according to the air state (such as humidity, temperature and density). For example, the speed of sound at sea level is about 331.5m/s (1193 km / h) at zero degree centigrade, 295m / S (1062km / h) at 10000 meters high, and 0.607m/s at every increase of 1 degree centigrade. The higher the temperature, the greater the speed of sound, It is found that the speed of sound in water is affected by temperature. There are salts in sea water, and the amount of salt also has an effect on the speed of sound. Among various factors, temperature has the greatest effect on the speed of sound. The speed of sound in water increases by about 4.6 m / s when the temperature increases by 1 ℃. It is generally believed that the speed of sound in sea water is 1500 m / s, which is about 4.5 times that in gas, The speed of sound in pure water is 1482.9 M / s, that in mercury is 1451 M / s, that in glycerol is 1923 M / s, that in alcohol is 1168 M / s, and that in carbon tetrachloride liquid is 935 M / s, For example, the velocity of P-wave in stainless steel rod is not the same as that of S-wave in 570 meters per second, The speed of longitudinal wave in polyethylene rod is only 920 M / s, which is not as fast as that in water. The soft rubber is elastic, and the sound wave can't walk inside. The speed is only 30-50 M / s, which is not as fast as that in air!
Because solid molecules can only vibrate near their equilibrium position, it is very easy to transfer energy between molecules, while liquid and gas molecules have no fixed equilibrium position, so it is relatively difficult for molecules to transfer energy. Therefore, sound travels fastest in solid

Experiment of measuring sound velocity in water
1. Write out the experimental steps 2. Use letters to know the known conditions in advance and the quantity to be measured in the experiment 3. The speed of sound in water is expressed by formula
It doesn't need to be very complicated and easy to understand

First, find a water tank and fill it with water, then prepare an ultrasonic transmitter to send out to one side of the water tank, and put a device that can reflect sound waves on the other side. When the sound wave returns to the ultrasonic transmitter again, record the time 2T, and then measure the distance s that the sound wave travels from left to right, then v = s / T