A course of junior high school physics [pressure and buoyancy], This is the physical simulation of Haidian District in Beijing in 2009 As shown in the figure (a cylindrical container contains a plastic box, in which an iron block floats on the water surface), the cylindrical container with bottom area S1 contains liquid with unknown density. Put a cube metal block with density ρ into the rectangular plastic box with bottom area S2 (the thickness of the plastic box can be ignored), The plastic box floats on the liquid surface (the liquid will not overflow the container), and its immersion depth is H1. If the metal block is taken out of the plastic box, it is tied under the plastic box with thin wire, and put into the liquid, the metal block does not contact the container, and the immersion depth of the plastic box is H2. Cut the thin wire, the metal block will sink to the bottom of the container, and the plastic box floats on the liquid surface, The depth of immersion is H3. If the plastic box is always upright without inclination, the pressure of the liquid on the bottom of the cylindrical container is reduced before and after the thin line is cut? Two supplementary points: 1. The density of the liquid in the container is unknown, and the expression should not contain ρ liquid. 2. The question is how much pressure has been reduced. Not why.

For the first time, the integral floating f-floating = G-box + ρ - gold v-gold g = ρ - liquid gs2h1 for the second time, the integral floating f-floating = G-box + ρ - gold v-gold g = ρ - liquid g (s2h2 + v-gold) for the second time, we get v-gold = S2 (h1-h2) for the third time

How to correctly understand the physical quantity in the formula of pressure and buoyancy in junior high school

The pressure is equal to the pressure divided by the pressure area, the pressure is the vertical pressure on the action surface, and the pressure area is the effective contact area with the action surface
Buoyancy = density of liquid * g * volume of liquid, liquid density, in other words, G acceleration of gravity, V row is the volume of the object, the volume that can be occupied in the liquid

Is there a shorthand method for the formula of scientific pressure and buoyancy in grade 2 of junior high school

According to the original record. Not long
Buoyancy to remember. Put a note
For example, when floating, f floats = g discharges = g objects = g in air - G in water = f up - f down
In suspension, f = g
Studious students,

The voltage of the rechargeable battery is 3.6V, the capacity is 500mA * h, how much energy is consumed for charging once, and how many times can it be charged for 1kW * H (excluding energy loss)

Capacity 500mA * H = 0.5ah
After charging, the capacity of the battery is 3.6 x 0.5 = 1.8V * ah = 1.8W * H
So it can charge 1000 / 1.8 = 556 times

What is the physical quantity of temperature?

Temperature is the physical quantity that indicates the degree of cold and hot of an object. In microcosmic sense, it is the intensity of molecular thermal movement of an object. Temperature can only be measured indirectly by some characteristics of the object changing with temperature, and the ruler used to measure the temperature value of an object is called temperature scale. It specifies the starting point (zero point) of temperature reading and the measuring range

What is the meaning of Hooke's law

Hooke's law is one of the basic laws of mechanics. It is applicable to the law of elasticity of all solid materials. It points out that: within the elastic limit, the deformation of a body is proportional to the external force causing the deformation. This law was discovered by British scientist Hooke, so it is called Hooke's law. The expression of Hooke's law is f = - KX or △ f = - K △ x, where k

The formula of Hooke's law?

Hooke's law
Within the elastic limit, the elastic force of a spring is directly proportional to its deformation (elongation or compression value)
F=k·x
Where: "F" means the spring force, which is the force exerted on the object when the spring deforms
"X" is the length of the spring extended or shortened. Note that "X" is based on the length of the spring when it is invisible, that is, x = x '- x0 or x = x0-x'
"K" is called stiffness coefficient of spring. It describes the elastic force generated by unit deformation. The large value of K indicates that the force required for deformation unit is large, or the spring is "hard". K is related to spring material, length and thickness. The international unit of K is n / m
If several identical springs are connected in series or in parallel, the stiffness coefficient of the new spring is no longer the original stiffness coefficient. As shown in figure (1), suppose that the stiffness coefficient of two springs with the same stiffness coefficient k after being connected in series is K1, then f = K1 · X. since the elastic force of point a is also f, it can be written for spring 1 that the stiffness coefficient of two springs with the same original length is K2, then f = K1 · X
F=k2·x
The number of parallel connection is larger than that of parallel connection

How to express Hooke's law?

Hooke's law
Within the elastic limit, the elastic force of the spring is proportional to its deformation (elongation or compression value)
Writing:
F=k·x
Where: "F" means the spring force, which is the force exerted on the object when the spring deforms
"X" is the extended or shortened length of the spring

Hooke's law formula

Hooke's law, also translated as Hooke's law, is a basic law in the theory of mechanical elasticity, which is expressed as: after a solid material is stressed, there is a linear relationship between the stress and strain (unit deformation) in the material

Meaning of physical quantities in Gauss theorem expression
I mean Gauss theorem in electric field, Q / E0! (actually it's not e, that letter can't be typed ~)
Can you explain the first floor more clearly

Electric flux of a closed surface: Φ = q / ε. Electric flux Φ is the electric field intensity × area. Q is the total number of charges in the surface. ε is a constant, equal to 1 / (4 π K), and K is the constant of Coulomb force. For example, there is a point charge Q, and the electric field strength e at the distance r is calculated. Take Q as the center of the sphere and R as the radius to make a sphere, and the sphere area is