Buoyancy formula of water Who knows

Buoyancy formula of water Who knows

F floating = P water * g * V row

Calculation formula for buoyancy of water saving in science exercise book No.5 of Grade 8
The total mass of the instrument and shell carried by the sounding balloon is 2.7 kg. The density of hydrogen in the balloon is 0.09 kg / m3, and the density of air is 1.29 kg / m3. What is the minimum mass of hydrogen in the balloon?

F floating = gtotal = mtotal g = 2.7x10 = 27N (two force balance)
F = PGV row
27 = 1.29x10xv row
Row v = 2.1m3
Vhydrogen = vdrain = 2.1m3
M hydrogen = P hydrogen V hydrogen = 0.09x2.1 = 0.189kg
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What is the buoyancy of water

This is the science of junior one
If an object is completely submerged in water and sinks to the bottom, then
F floating = V row = density of object * Volume * g (9.8kg / m3)
If an object is completely submerged and suspended in water, then
F is equal to the gravity of the object
In a word, f is always in accordance with Archimedes law
There is no definite value for the buoyancy of water!
Give it to me

Einstein's mass energy equation
What is this?

E = MC ^ 2, where e is the energy released completely, M is the mass, and C is the speed of light. The derivation of the mass energy equation should first recognize two assumptions of special relativity: 1. The velocity of spherical light emitted by any light source is isotropic in all inertial reference frames, and it is always C 2

The most concise summary of junior high school physics knowledge

1、 There are only two kinds of electric charge in nature. The electric charge on the glass rod rubbed by silk is called positive charge; the electric charge on the rubber rod rubbed by fur is called negative charge

How to understand Einstein's mass energy equation

Here is my copy of the content, I hope to help you
Einstein's famous mass energy equation E = MC ^ 2, e for energy, m for mass, and C for the speed of light. An important result of relativity is the relationship between mass and energy. Mass and energy are not interchangeable and are based on special relativity, In 1915, he put forward the general theory of relativity. In June 1905, Einstein published his paper "an enlightening view on the generation and transformation of light", which explained the essence of light, which also won him the Nobel Prize in physics in 1921
Derivation of mass energy equation
First of all, two hypotheses of special relativity should be accepted: 1. The velocity of spherical light emitted by any light source in all inertial reference frames is isotropic, and it is always C 2. The physical laws in all inertial reference frames are the same
If your walking speed is V and you are on a bus traveling at speed u, then when you walk in the same direction as the bus, your speed to the ground is U + V, and U-V when you walk in the opposite direction. You spend one minute in the car and others spend one minute on the ground. This is the common sense in our minds. It is also the famous Galileo transformation in physics, The theory holds that space is independent and has nothing to do with all kinds of objects moving in it, while time passes uniformly and linearly, which is the same to any observer
The above changes are in contradiction with the hypothesis of special relativity
In fact, before Einstein put forward the special theory of relativity, people observed many phenomena that were inconsistent with common sense. In order to correct the collapse of the classical physics building, physicist Lorentz proposed Lorentz transformation, but he could not explain why this phenomenon occurred, Lorentz transformation is an empirical formula based on the observed facts at that time, but it can be deduced from the pure theory of relativity
Then according to this formula, we can deduce the relationship between mass and velocity, that is, the time will slow down with the increase of velocity, the mass will increase and the length will decrease
The actual mass of an object is the sum of its static mass and its extra mass through motion
When the external force acts on a free particle with a static mass of M0, the increment of kinetic energy of the particle is DEK = f · DS for every displacement DS. If the external force and displacement are in the same direction, the above formula is DEK = FDS. If the time of the external force acting on the particle is DT, the momentum increment of the particle is DP = FDT. Considering v = DS / DT, the above two formulas are divided, That is to say, the expression of the velocity of the particle is v = DEK / DP, that is, DEK = VD (MV) = V ^ 2DM + mvdv. The formula that Einstein's mass changes with the velocity of the object is squared to get m ^ 2 (C ^ 2-V ^ 2) = M0 ^ 2C ^ 2. The differential equation is mvdv = (C ^ 2-V ^ 2) DM, which is substituted into the above formula to get DEK = C ^ 2DM, When v = 0, mass m = M0, kinetic energy EK = 0. According to the above formula, we can get ∫ ek0dek = ∫ m0m C ^ 2DM (from M0 to m) EK = MC ^ 2-m0c ^ 2
The above formula is the kinetic energy expression in the theory of relativity. Einstein introduced a unique idea never seen before in classical mechanics. He called m0c ^ 2 the static energy of an object and MC ^ 2 the energy in motion. We use E0 and e to express them respectively: e = MC ^ 2, E0 = m0c ^ 2
Derivation: first, the special theory of relativity is obtained
Lorentz factor γ = 1 / sqrt (1 - V ^ 2 / C ^ 2)
Therefore, the mass of the moving object m (V) = γ M0 = M0 / (1 - V ^ 2 / C ^ 2)
Then Taylor expansion is used
　　1/sqrt(1 - v^2/c^2)=1+1/2*v^2/c^2+.
M (V) C ^ 2 = γ m0c ^ 2 = m0c ^ 2 / (1 - V ^ 2 / C ^ 2) = m0c ^ 2 + 1 / 2m0v ^ 2 +
Where m 0C ^ 2 is the static energy, 1 / 2m0v ^ 2 is the kinetic energy at low speed, and the ellipsis is the energy of higher order
Unit
E = MC ^ 2, e is the unit of energy is Joule (J), M is the unit of mass is kilogram (kg), C is the speed of light! C = 3 * 10 ^ 8
Does e = MC ^ 2 violate the law of conservation of mass?
The mass energy equation does not violate the law of conservation of mass. The law of conservation of mass means that in any isolated system, no matter what changes or processes take place, the total mass always remains unchanged. In other words, chemical changes can only change the composition of matter, but can not create or destroy matter. Therefore, the law is also called the law of indestructibility of matter
The mass energy equation expresses the relationship between mass and energy, so it does not violate the law of conservation of mass. At the same time, the formula shows that matter can be transformed into radiant energy, and radiant energy can also be transformed into matter. This phenomenon does not mean that matter will be destroyed, but that the static mass of matter will be transformed into another form of motion, So after the 20th century, the law of conservation of mass and energy was developed from the original law of conservation of mass and energy, which is called the law of conservation of mass and energy
On the relationship between mass and energy:
Mass and energy are one thing and two expressions of one thing. Mass is introverted energy and energy is explicit mass
As Einstein said: "mass is energy, energy is mass. Time is space, space is time."
English reading of mass energy equation
　　E equals M C squared.
　　E is equal to M C squared.
It can also be interpreted
　　Energy is equal to mass multiplied by the square of the speed of light.
The mass energy equation is divided into total energy and static mass
Three expressions of mass energy equation
Expression 1: E0 = m0c ^ 2
In the above formula, M0 is the static mass of the object and m0c is the static energy of the object
　　E=mc^2.
Expression 2: EV = MVC ^ 2
MC is the energy of a body in motion, that is, the sum of its static energy and kinetic energy
Expression 3: Δ e = Δ MC ^ 2
In the above formula, Δ m is usually the change of the static mass of the object, that is, the mass loss. Δ e is the change of the static energy of the object. In fact, this expression is the differential form of expression 1. This expression is the most commonly used, and is also the expression most likely to be misunderstood by students
Static energy of objects
The static energy of an object is its total internal energy, including the kinetic energy of molecular motion, the potential energy of intermolecular interaction, the chemical energy that binds atoms together, the electromagnetic energy that binds nuclei and electrons together, and the binding energy of protons and neutrons in nuclei The revelation of the static energy of objects is one of the most important corollaries of relativity. It points out that there is still motion in the static particles. Particles with a certain mass have a certain internal motion energy. Conversely, particles with a certain internal motion energy show a certain habitual mass, For example, when the pion decays into two photons, because the rest mass of the photon is zero and there is no rest energy, so the rest energy in the pion is zero
The connection between mass and energy
In classical mechanics, mass and energy are independent of each other, but in relativistic mechanics, energy and mass are just two different aspects of the mechanical properties of objects. In this way, the extension of the concept of mass in relativity is greatly expanded. Einstein pointed out: "if an object emits energy Δ E in the form of radiation, The mass of an object is a measure of the energy it contains. "He also pointed out:" this result has special theoretical significance, because in this result, The inertial mass and energy of a system of things appear in the same attitude It seems much more natural to understand any inertial mass as a storage of energy. "In this way, the law of conservation of mass and the law of conservation of energy, which are independent of each other in classical mechanics, are combined to form a unified" law of conservation of mass and energy ", which fully reflects the unity of matter and motion
The mass energy equation shows that mass and energy are inseparable and related. On the one hand, any material system can use mass m to mark its quantity and energy E to mark its quantity; on the other hand, when the energy of one system decreases, its mass decreases correspondingly; when the energy of another system increases, its mass increases correspondingly
Mass loss and mass conservation
When a group of particles constitute a composite body, due to the interaction energy and kinetic energy of relative motion between the particles, when the whole body is stationary, its total energy is generally not equal to the sum of the rest energy of all particles, that is, E0 ≠Σ mioc, where mi0 is the rest mass of the ith particle. The difference between the two is called the binding energy of the body: Δ e = ∑ mioc-e0, The static mass M0 = E0 / C of a body is not equal to the sum of the static masses of its particles, and the difference between them is called mass defect: Δ M = ∑ mio-m0. There is a relationship between mass defect and binding energy: Δ e = Δ MC
Because in the middle school physics teaching material, this kind of