八年级下册物理提纲（The eighth grade physics outline）.doc

八年级下册物理提纲（The eighth grade physics outline） Pressure p is equal to F over S P = rho g h p = F/S is applicable to solid, liquid and gas P = rho g h applied to the vertical solid column P = rho g h can directly calculate the liquid pressure 1 standard atmospheric pressure = 76 cmHg column = 1.01 x 105 Pa = 10.3 m water column Buoyancy = G - F Floating and levitating: F float = G F float = G row = rho G V row Find the appropriate formula to calculate buoyancy: Objects buoyancy condition (premises: the object is immersed in liquid and only by buoyancy and gravity) : F float G (rho liquid rho) float to float. F float = G (rho liquid = rho) suspension F float G (rho) sink The pressure at the bottom of the container of the shape rule is: F = p * S = PGH * S * g = g = m liquid Pressure P = F/S = (G liquid + G capacity)/S Chapter 9: buoyancy and lift Cases of the topic [example 1] there is a alloy block of 10 kg, all submerged in water, the force of 80N can be used to hold it. What is the buoyancy of the alloy block at this time? According to G = mg, metal block gravity can be obtained, and the buoyancy force is the difference between gravity and pull. G = mg = 10kg * 9.8 N/kg = 98N F float = G - F la = 98N - 80N = 18N Answer: the buoyancy of the metal block is 18N. [example 2] a cube iron, under a depth of water, the upper surface is subjected to 15N pressure and the bottom surface is subjected to 20N pressure, while the iron block is subjected to the buoyancy of N; When the iron is sinking to a certain position, the pressure increases to 20N when the upper bottom is increased to 20N, and the bottom pressure is ________N. The cause of buoyancy is the pressure difference between the upper and lower surfaces of the object. As the object sinks, the pressure on each surface becomes larger, but the pressure difference is constant F float = F - F = 20N - 15N = 5N, F = F = F = 20N + 5N = 25N. [answer] 5, 25. The volume is 500dm5, the mass is 450kg and the mine is thrown into th