密度和电阻分别是力学和电学中的重要物理量,这两个物理量有个共同特点,都反映物体本身的一种特性.密度的计算公式是ρ=m/V,密度只与物质的种类有关系,不随物体本身质量或体积而改变.电阻的计算公式是R=U/I,导体的电阻只与本身的材料、长短、粗细及所处环境温度有关,不随导体两端的电压或通过它的电流而改变.教学中让学生对这两个物理量进行对比分析加以理解.测量密度时,主要采用测物体的质量和体积,用ρ=m/V Density and resistance are important physical quantities in mechanics and electronics, respectively. These two physical quantities have a common feature and both reflect a characteristic of the object itself. The density formula is ρ=m/V, and the density is only related to the type of substance. It does not change with the mass or volume of the object itself. The formula for the resistance is R = U/I. The resistance of the conductor is only related to its material, length, thickness, and ambient temperature. It does not follow the voltage across the conductor or the current through it. The change. Teaching students to the two physical quantities comparative analysis to understand. When measuring density, the main use of measuring the mass and volume of objects, with ρ = m / V